The C++ APIs in html5.h define the Emscripten low-level glue bindings to interact with HTML5 events from native code.
Tip
The C++ APIs map closely to their equivalent HTML5 JavaScript APIs. The HTML5 specifications listed below provide additional detailed reference “over and above” the information provided in this document.
In addition, the Test/Example code can be reviewed to see how the code is used.
The HTML5 specifications for APIs that are mapped by html5.h include:
Table of Contents
Most of these APIs use an event-based architecture; functionality is accessed by registering a callback function that will be called when the event occurs.
Note
The Gamepad API is currently an exception, as only a polling API is available. For some APIs, both an event-based and a polling-based model are exposed.
The typical format of registration functions is as follows (some methods may omit various parameters):
EMSCRIPTEN_RESULT emscripten_set_some_callback( const char *target, // ID of the target HTML element. void *userData, // User-defined data to be passed to the callback. bool useCapture, // Whether or not to use capture. em_someevent_callback_func callback // Callback function. );
The target
parameter is the ID of the HTML element to which the callback registration is to be applied. This field has the following special meanings:
EMSCRIPTEN_EVENT_TARGET_WINDOW
: The event listener is applied to the JavaScriptwindow
object.
EMSCRIPTEN_EVENT_TARGET_DOCUMENT
: The event listener is applied to the JavaScriptdocument
object.
EMSCRIPTEN_EVENT_TARGET_SCREEN
: The event listener is applied to the JavaScriptwindow.screen
object.
0
orNULL
: If building with the option-sDISABLE_DEPRECATED_FIND_EVENT_TARGET_BEHAVIOR
(default),NULL
denotes an invalid element. If building with legacy option-sDISABLE_DEPRECATED_FIND_EVENT_TARGET_BEHAVIOR=0
(not recommended), a default element is chosen automatically based on the event type.
#canvas
: If building with legacy option-sDISABLE_DEPRECATED_FIND_EVENT_TARGET_BEHAVIOR=0
(not recommended), the event listener is applied to the Emscripten default WebGL canvas element. If building with the option-sDISABLE_DEPRECATED_FIND_EVENT_TARGET_BEHAVIOR
(default),#canvas
is interpreted as a CSS query selector: “the first element with CSS ID ‘canvas’”.Any other string: A CSS selector lookup is performed to the DOM with the passed string, and the event listener is applied to the first element that matches the query.
If the above are insufficient for you, you can add custom mappings in JavaScript using something like
specialHTMLTargets["!canvas"] = Module.canvas;
That will let !canvas
map to the canvas held in Module.canvas. (You can write
that JavaScript in an EM_JS
or EM_ASM
block that happens before you
call the registration function, for example.)
The userData
parameter is a user-defined value that is passed (unchanged) to the registered event callback. This can be used to, for example, pass a pointer to a C++ class or similarly to enclose the C API in a clean object-oriented manner.
The useCapture
parameter maps to useCapture
in EventTarget.addEventListener. It indicates whether or not to initiate capture: if true
the callback will be invoked only for the DOM capture and target phases; if false
the callback will be triggered during the target and bubbling phases. See DOM Level 3 Events for a more detailed explanation.
Most functions return the result using the type EMSCRIPTEN_RESULT
. Zero and positive values denote success. Negative values signal failure. None of the functions fail or abort by throwing a JavaScript or C++ exception. If a particular browser does not support the given feature, the value EMSCRIPTEN_RESULT_NOT_SUPPORTED
will be returned at the time the callback is registered.
When the event occurs the callback is invoked with the relevant event “type” (for example EMSCRIPTEN_EVENT_CLICK
), a struct
containing the details of the event that occurred, and the userData
that was originally passed to the registration function. The general format of the callback function is:
typedef bool (*em_someevent_callback_func) // Callback function. Return true if event is "consumed".
(
int eventType, // The type of event.
const EmscriptenSomeEvent *someEvent, // Information about the event.
void *userData // User data passed from the registration function.
);
Callback handlers that return an bool
may specify true
to signal that the handler consumed the event (this suppresses the default action for that event by calling its .preventDefault();
member). Returning false
indicates that the event was not consumed — the default browser event action is carried out and the event is allowed to pass on/bubble up as normal.
Calling a registration function with a null
pointer for the callback causes a de-registration of that callback from the given target
element. All event handlers are also automatically unregistered when the C exit()
function is invoked during the atexit
handler pass. Either use the function emscripten_set_main_loop()
or set Module.noExitRuntime = true;
to make sure that leaving main()
will not immediately cause an exit()
and clean up the event handlers.
Some functions, including emscripten_request_pointerlock()
and emscripten_request_fullscreen()
, are affected by web security.
While the functions can be called anywhere, the actual “requests” can only be raised inside the handler for a user-generated event (for example a key, mouse or touch press/release).
When porting code, it may be difficult to ensure that the functions are called inside appropriate event handlers (so that the requests are raised immediately). As a convenience, developers can set deferUntilInEventHandler=true
to automatically defer insecure requests until the user next presses a keyboard or mouse button. This simplifies porting, but often results in a poorer user experience. For example, the user must click once on the canvas to hide the pointer or transition to full screen.
Where possible, the functions should only be called inside appropriate event handlers. Setting deferUntilInEventHandler=false
causes the functions to abort with an error if the request is refused due to a security restriction: this is a useful mechanism for discovering instances where the functions are called outside the handler for a user-generated event.
The HTML5 test code demonstrates how to use this API:
EM_UTF8
¶This is the Emscripten type for a UTF8 string (maps to a char
). This is used for node names, element ids, etc.
Most functions in this API return a result of type EMSCRIPTEN_RESULT
. None of the functions fail or abort by throwing a JavaScript or C++ exception. If a particular browser does not support the given feature, the value EMSCRIPTEN_RESULT_NOT_SUPPORTED
will be returned at the time the callback is registered.
EMSCRIPTEN_RESULT
¶This type is used to return the result of most functions in this API. Zero and positive values denote success, while negative values signal failure. Possible values are listed below.
EMSCRIPTEN_RESULT_SUCCESS
¶The operation succeeded.
EMSCRIPTEN_RESULT_DEFERRED
¶The requested operation cannot be completed now for web security reasons, and has been deferred for completion in the next event handler.
EMSCRIPTEN_RESULT_NOT_SUPPORTED
¶The given operation is not supported by this browser or the target element. This value will be returned at the time the callback is registered if the operation is not supported.
EMSCRIPTEN_RESULT_FAILED_NOT_DEFERRED
¶The requested operation could not be completed now for web security reasons. It failed because the user requested the operation not be deferred.
EMSCRIPTEN_RESULT_INVALID_TARGET
¶The operation failed because the specified target element is invalid.
EMSCRIPTEN_RESULT_UNKNOWN_TARGET
¶The operation failed because the specified target element was not found.
EMSCRIPTEN_RESULT_INVALID_PARAM
¶The operation failed because an invalid parameter was passed to the function.
EMSCRIPTEN_RESULT_FAILED
¶Generic failure result message, returned if no specific result is available.
EMSCRIPTEN_RESULT_NO_DATA
¶The operation failed because no data is currently available.
EmscriptenKeyboardEvent
¶The event structure passed in keyboard events: keypress
, keydown
and keyup
.
Note that since the DOM Level 3 Events spec is very recent at the time of writing (2014-03), uniform support for the different fields in the spec is still in flux. Be sure to check the results in multiple browsers. See the unmerged pull request #2222 for an example of how to interpret the legacy key events.
timestamp
¶Absolute wallclock time when the data was recorded (milliseconds).
key
¶The printed representation of the pressed key.
Maximum size 32 char
(i.e. EM_UTF8 key[32]
).
code
¶A string that identifies the physical key being pressed. The value is not affected by the current keyboard layout or modifier state, so a particular key will always return the same value.
Maximum size 32 char
(i.e. EM_UTF8 code[32]
).
location
¶Indicates the location of the key on the keyboard. One of the DOM_KEY_LOCATION
values.
ctrlKey
¶shiftKey
¶altKey
¶metaKey
¶Specifies which modifiers were active during the key event.
repeat
¶Specifies if this keyboard event represents a repeated press.
locale
¶A locale string indicating the configured keyboard locale. This may be an empty string if the browser or device doesn’t know the keyboard’s locale.
Maximum size 32 char (i.e. EM_UTF8 locale[32]
).
charValue
¶The following fields are values from previous versions of the DOM key events specifications. See the character representation of the key. This is the field char
from the docs, but renamed to charValue
to avoid a C reserved word.
Maximum size 32 char
(i.e. EM_UTF8 charValue[32]
).
Warning
This attribute has been dropped from DOM Level 3 events.
charCode
¶The Unicode reference number of the key; this attribute is used only by the keypress event. For keys whose char
attribute contains multiple characters, this is the Unicode value of the first character in that attribute.
Warning
This attribute is deprecated, you should use the field key
instead, if available.
keyCode
¶A system and implementation dependent numerical code identifying the unmodified value of the pressed key.
Warning
This attribute is deprecated, you should use the field key
instead, if available.
which
¶A system and implementation dependent numeric code identifying the unmodified value of the pressed key; this is usually the same as keyCode
.
Warning
This attribute is deprecated, you should use the field key
instead, if available. Note thought that while this field is deprecated, the cross-browser support for which
may be better than for the other fields, so experimentation is recommended. Read issue https://github.com/emscripten-core/emscripten/issues/2817 for more information.
em_key_callback_func
¶Function pointer for the keypress callback functions
, defined as:
typedef bool (*em_key_callback_func)(int eventType, const EmscriptenKeyboardEvent *keyEvent, void *userData);
eventType (int) – The type of key event
.
keyEvent (const EmscriptenKeyboardEvent*) – Information about the key event that occurred.
userData (void*) – The userData
originally passed to the registration function.
true
(non zero) to indicate that the event was consumed by the callback handler.
bool
emscripten_set_keypress_callback
(const char *target, void *userData, bool useCapture, em_key_callback_func callback)¶emscripten_set_keydown_callback
(const char *target, void *userData, bool useCapture, em_key_callback_func callback)¶emscripten_set_keyup_callback
(const char *target, void *userData, bool useCapture, em_key_callback_func callback)¶Registers a callback function for receiving browser-generated keyboard input events.
target (const char*) – Target HTML element id.
userData (void*) – User-defined data to be passed to the callback (opaque to the API).
useCapture (bool) – Set true
to use capture.
callback (em_key_callback_func) – A callback function. The function is called with the type of event, information about the event, and user data passed from this registration function. The callback should return true
if the event is consumed.
EMSCRIPTEN_RESULT_SUCCESS
, or one of the other result values.
Note
To receive events, the element must be focusable, see https://github.com/emscripten-core/emscripten/pull/7484#issuecomment-437887001
EmscriptenMouseEvent
¶The event structure passed in mouse events: click, mousedown, mouseup, dblclick, mousemove, mouseenter and mouseleave.
timestamp
¶Absolute wallclock time when the data was recorded (milliseconds).
ctrlKey
¶shiftKey
¶altKey
¶metaKey
¶Specifies which modifiers were active during the mouse event.
Identifies which pointer device button changed state (see MouseEvent.button):
0 : Left button
1 : Middle button (if present)
2 : Right button
A bitmask that indicates which combinations of mouse buttons were being held down at the time of the event.
movementX
¶long movementY;
If pointer lock is active, these two extra fields give relative mouse movement since the last event.
targetX
¶targetY
¶These fields give the mouse coordinates mapped relative to the coordinate space of the target DOM element receiving the input events (Emscripten-specific extension; coordinates are rounded down to the nearest integer).
canvasX
¶canvasY
¶These fields give the mouse coordinates mapped to the Emscripten canvas client area (Emscripten-specific extension; coordinates are rounded down the nearest integer).
padding
¶Internal, and can be ignored.
Note
Implementers only: pad this struct to multiple of 8 bytes to make WheelEvent
unambiguously align to 8 bytes.
em_mouse_callback_func
¶Function pointer for the mouse event callback functions
, defined as:
typedef bool (*em_mouse_callback_func)(int eventType, const EmscriptenMouseEvent *mouseEvent, void *userData);
eventType (int) – The type of mouse event
.
mouseEvent (const EmscriptenMouseEvent*) – Information about the mouse event that occurred.
userData (void*) – The userData
originally passed to the registration function.
true
(non zero) to indicate that the event was consumed by the callback handler.
bool
emscripten_set_click_callback
(const char *target, void *userData, bool useCapture, em_mouse_callback_func callback)¶emscripten_set_mousedown_callback
(const char *target, void *userData, bool useCapture, em_mouse_callback_func callback)¶emscripten_set_mouseup_callback
(const char *target, void *userData, bool useCapture, em_mouse_callback_func callback)¶emscripten_set_dblclick_callback
(const char *target, void *userData, bool useCapture, em_mouse_callback_func callback)¶emscripten_set_mousemove_callback
(const char *target, void *userData, bool useCapture, em_mouse_callback_func callback)¶emscripten_set_mouseenter_callback
(const char *target, void *userData, bool useCapture, em_mouse_callback_func callback)¶emscripten_set_mouseleave_callback
(const char *target, void *userData, bool useCapture, em_mouse_callback_func callback)¶Registers a callback function for receiving browser-generated mouse input events.
target (const char*) – Target HTML element id.
userData (void*) – User-defined data to be passed to the callback (opaque to the API).
useCapture (bool) – Set true
to use capture.
callback (em_mouse_callback_func) – A callback function. The function is called with the type of event, information about the event, and user data passed from this registration function. The callback should return true
if the event is consumed.
EMSCRIPTEN_RESULT_SUCCESS
, or one of the other result values.
emscripten_get_mouse_status
(EmscriptenMouseEvent *mouseState)¶Returns the most recently received mouse event state.
Note that for this function call to succeed, emscripten_set_xxx_callback
must have first been called with one of the mouse event types and a non-zero callback function pointer to enable the Mouse state capture.
mouseState (EmscriptenMouseEvent*) – The most recently received mouse event state.
EMSCRIPTEN_RESULT_SUCCESS
, or one of the other result values.
EMSCRIPTEN_EVENT_WHEEL
¶Emscripten wheel event.
EmscriptenWheelEvent
¶The event structure passed in mousewheel events.
mouse
¶Specifies general mouse information related to this event.
deltaX
¶deltaY
¶deltaZ
¶Movement of the wheel on each of the axis. Note that these values may be fractional, so you should avoid simply casting them to integer, or it might result in scroll values of 0. The positive Y scroll direction is when scrolling the page downwards (page CSS pixel +Y direction), which corresponds to scrolling the mouse wheel downwards (away from the screen) on Windows, Linux, and also on macOS when the ‘natural scroll’ option is disabled.
deltaMode
¶One of the DOM_DELTA_
values that indicates the units of measurement for the delta values.
em_wheel_callback_func
¶Function pointer for the wheel event callback functions
, defined as:
typedef bool (*em_wheel_callback_func)(int eventType, const EmscriptenWheelEvent *wheelEvent, void *userData);
eventType (int) – The type of wheel event (EMSCRIPTEN_EVENT_WHEEL
).
wheelEvent (const EmscriptenWheelEvent*) – Information about the wheel event that occurred.
userData (void*) – The userData
originally passed to the registration function.
true
(non zero) to indicate that the event was consumed by the callback handler.
bool
emscripten_set_wheel_callback
(const char *target, void *userData, bool useCapture, em_wheel_callback_func callback)¶Registers a callback function for receiving browser-generated mousewheel events.
target (const char*) – Target HTML element id.
userData (void*) – User-defined data to be passed to the callback (opaque to the API).
useCapture (bool) – Set true
to use capture.
callback (em_wheel_callback_func) – A callback function. The function is called with the type of event, information about the event, and user data passed from this registration function. The callback should return true
if the event is consumed.
EMSCRIPTEN_RESULT_SUCCESS
, or one of the other result values.
EmscriptenUiEvent
¶The event structure passed in DOM element UIEvent events: resize and scroll.
detail
¶For resize and scroll events this is always zero.
documentBodyClientWidth
¶documentBodyClientHeight
¶The clientWidth/clientHeight of the document.body
element.
windowOuterWidth
¶int windowOuterHeight;
The outerWidth/outerHeight of the browser window.
em_ui_callback_func
¶Function pointer for the UI event callback functions
, defined as:
typedef bool (*em_ui_callback_func)(int eventType, const EmscriptenUiEvent *uiEvent, void *userData);
eventType (int) – The type of UI event (EMSCRIPTEN_EVENT_RESIZE
).
uiEvent (const EmscriptenUiEvent*) – Information about the UI event that occurred.
userData (void*) – The userData
originally passed to the registration function.
true
(non zero) to indicate that the event was consumed by the callback handler.
bool
emscripten_set_resize_callback
(const char *target, void *userData, bool useCapture, em_ui_callback_func callback)¶emscripten_set_scroll_callback
(const char *target, void *userData, bool useCapture, em_ui_callback_func callback)¶Registers a callback function for receiving DOM element resize and scroll events.
Note
For the resize
callback, pass in target = EMSCRIPTEN_EVENT_TARGET_WINDOW
to get resize
events from the Window
object.
The DOM3 Events specification only requires that the Window
object sends resize events. It is valid to register a resize
callback on other DOM elements, but the browser is not required to fire resize
events for these.
target (const char*) – Target HTML element id.
userData (void*) – User-defined data to be passed to the callback (opaque to the API).
useCapture (bool) – Set true
to use capture.
callback (em_ui_callback_func) – A callback function. The function is called with the type of event, information about the event, and user data passed from this registration function. The callback should return true
if the event is consumed.
EMSCRIPTEN_RESULT_SUCCESS
, or one of the other result values.
em_focus_callback_func
¶Function pointer for the focus event callback functions
, defined as:
typedef bool (*em_focus_callback_func)(int eventType, const EmscriptenFocusEvent *focusEvent, void *userData);
eventType (int) – The type of focus event (EMSCRIPTEN_EVENT_BLUR
).
focusEvent (const EmscriptenFocusEvent*) – Information about the focus event that occurred.
userData (void*) – The userData
originally passed to the registration function.
true
(non zero) to indicate that the event was consumed by the callback handler.
bool
emscripten_set_blur_callback
(const char *target, void *userData, bool useCapture, em_focus_callback_func callback)¶emscripten_set_focus_callback
(const char *target, void *userData, bool useCapture, em_focus_callback_func callback)¶emscripten_set_focusin_callback
(const char *target, void *userData, bool useCapture, em_focus_callback_func callback)¶emscripten_set_focusout_callback
(const char *target, void *userData, bool useCapture, em_focus_callback_func callback)¶Registers a callback function for receiving DOM element blur, focus, focusin and focusout events.
target (const char*) – Target HTML element id.
userData (void*) – User-defined data to be passed to the callback (opaque to the API).
useCapture (bool) – Set true
to use capture.
callback (em_focus_callback_func) – A callback function. The function is called with the type of event, information about the event, and user data passed from this registration function. The callback should return true
if the event is consumed.
EMSCRIPTEN_RESULT_SUCCESS
, or one of the other result values.
EMSCRIPTEN_EVENT_DEVICEORIENTATION
¶Emscripten deviceorientation
events.
EmscriptenDeviceOrientationEvent
¶The event structure passed in the deviceorientation event.
alpha
¶beta
¶gamma
¶The orientation of the device in terms of the transformation from a coordinate frame fixed on the Earth to a coordinate frame fixed in the device.
The image (source: dev.opera.com) and definitions below illustrate the co-ordinate frame:
absolute
¶If false
, the orientation is only relative to some other base orientation, not to the fixed coordinate frame.
em_deviceorientation_callback_func
¶Function pointer for the orientation event callback functions
, defined as:
typedef bool (*em_deviceorientation_callback_func)(int eventType, const EmscriptenDeviceOrientationEvent *deviceOrientationEvent, void *userData);
eventType (int) – The type of orientation event (EMSCRIPTEN_EVENT_DEVICEORIENTATION
).
deviceOrientationEvent (const EmscriptenDeviceOrientationEvent*) – Information about the orientation event that occurred.
userData (void*) – The userData
originally passed to the registration function.
true
(non zero) to indicate that the event was consumed by the callback handler.
bool
emscripten_set_deviceorientation_callback
(void *userData, bool useCapture, em_deviceorientation_callback_func callback)¶Registers a callback function for receiving the deviceorientation event.
userData (void*) – User-defined data to be passed to the callback (opaque to the API).
useCapture (bool) – Set true
to use capture.
callback (em_deviceorientation_callback_func) – A callback function. The function is called with the type of event, information about the event, and user data passed from this registration function. The callback should return true
if the event is consumed.
EMSCRIPTEN_RESULT_SUCCESS
, or one of the other result values.
emscripten_get_deviceorientation_status
(EmscriptenDeviceOrientationEvent *orientationState)¶Returns the most recently received deviceorientation
event state.
Note that for this function call to succeed, emscripten_set_deviceorientation_callback()
must have first been called with one of the mouse event types and a non-zero callback function pointer to enable the deviceorientation
state capture.
orientationState (EmscriptenDeviceOrientationEvent*) – The most recently received deviceorientation
event state.
EMSCRIPTEN_RESULT_SUCCESS
, or one of the other result values.
EMSCRIPTEN_EVENT_DEVICEMOTION
¶Emscripten devicemotion event.
EmscriptenDeviceMotionEvent
¶The event structure passed in the devicemotion event.
accelerationX
¶accelerationY
¶accelerationZ
¶Acceleration of the device excluding gravity.
accelerationIncludingGravityX
¶accelerationIncludingGravityY
¶accelerationIncludingGravityZ
¶Acceleration of the device including gravity.
rotationRateAlpha
¶rotationRateBeta
¶rotationRateGamma
¶The rotational delta of the device.
supportedFields
¶A bitfield that is a combination of EMSCRIPTEN_DEVICE_MOTION_EVENT_SUPPORTS_* fields that specifies the different fields of this structure that the current browser supports. If for example the EMSCRIPTEN_DEVICE_MOTION_EVENT_SUPPORTS_ACCELERATION bit is not present in this field, then the accelerationX/Y/Z fields of this structure should be assumed to not be valid.
em_devicemotion_callback_func
¶Function pointer for the devicemotion event callback functions
, defined as:
typedef bool (*em_devicemotion_callback_func)(int eventType, const EmscriptenDeviceMotionEvent *deviceMotionEvent, void *userData);
eventType (int) – The type of devicemotion event (EMSCRIPTEN_EVENT_DEVICEMOTION
).
deviceMotionEvent (const EmscriptenDeviceMotionEvent*) – Information about the devicemotion event that occurred.
userData (void*) – The userData
originally passed to the registration function.
true
(non zero) to indicate that the event was consumed by the callback handler.
bool
emscripten_set_devicemotion_callback
(void *userData, bool useCapture, em_devicemotion_callback_func callback)¶Registers a callback function for receiving the devicemotion event.
userData (void*) – User-defined data to be passed to the callback (opaque to the API).
useCapture (bool) – Set true
to use capture.
callback (em_devicemotion_callback_func) – A callback function. The function is called with the type of event, information about the event, and user data passed from this registration function. The callback should return true
if the event is consumed.
EMSCRIPTEN_RESULT_SUCCESS
, or one of the other result values.
emscripten_get_devicemotion_status
(EmscriptenDeviceMotionEvent *motionState)¶Returns the most recently received devicemotion event state.
Note that for this function call to succeed, emscripten_set_devicemotion_callback()
must have first been called with one of the mouse event types and a non-zero callback function pointer to enable the devicemotion
state capture.
motionState (EmscriptenDeviceMotionEvent*) – The most recently received devicemotion
event state.
EMSCRIPTEN_RESULT_SUCCESS
, or one of the other result values.
EMSCRIPTEN_EVENT_ORIENTATIONCHANGE
¶Emscripten orientationchange event.
EMSCRIPTEN_ORIENTATION_UNKNOWN
¶Either the orientation API is not supported or the orientation type is not known.
EMSCRIPTEN_ORIENTATION_PORTRAIT_PRIMARY
¶Primary portrait mode orientation.
EMSCRIPTEN_ORIENTATION_PORTRAIT_SECONDARY
¶Secondary portrait mode orientation.
EMSCRIPTEN_ORIENTATION_LANDSCAPE_PRIMARY
¶Primary landscape mode orientation.
EMSCRIPTEN_ORIENTATION_LANDSCAPE_SECONDARY
¶Secondary landscape mode orientation.
EmscriptenOrientationChangeEvent
¶The event structure passed in the orientationchange event.
orientationIndex
¶One of the EM_ORIENTATION_PORTRAIT_xxx
fields, or EMSCRIPTEN_ORIENTATION_UNKNOWN
if unknown.
orientationAngle
¶Emscripten-specific extension: Some browsers refer to window.orientation
, so report that as well.
Orientation angle in degrees. 0: “default orientation”, i.e. default upright orientation to hold the mobile device in. Could be either landscape or portrait.
em_orientationchange_callback_func
¶Function pointer for the orientationchange event callback functions
, defined as:
typedef bool (*em_orientationchange_callback_func)(int eventType, const EmscriptenOrientationChangeEvent *orientationChangeEvent, void *userData);
eventType (int) – The type of orientationchange event (EMSCRIPTEN_EVENT_ORIENTATIONCHANGE
).
orientationChangeEvent (const EmscriptenOrientationChangeEvent*) – Information about the orientationchange event that occurred.
userData (void*) – The userData
originally passed to the registration function.
true
(non zero) to indicate that the event was consumed by the callback handler.
bool
emscripten_set_orientationchange_callback
(void *userData, bool useCapture, em_orientationchange_callback_func callback)¶Registers a callback function for receiving the orientationchange event.
userData (void*) – User-defined data to be passed to the callback (opaque to the API).
useCapture (bool) – Set true
to use capture.
callback (em_orientationchange_callback_func) – A callback function. The function is called with the type of event, information about the event, and user data passed from this registration function. The callback should return true
if the event is consumed.
EMSCRIPTEN_RESULT_SUCCESS
, or one of the other result values.
emscripten_get_orientation_status
(EmscriptenOrientationChangeEvent *orientationStatus)¶Returns the current device orientation state.
orientationStatus (EmscriptenOrientationChangeEvent*) – The most recently received orientation state.
EMSCRIPTEN_RESULT_SUCCESS
, or one of the other result values.
emscripten_lock_orientation
(int allowedOrientations)¶Locks the screen orientation to the given set of allowed orientations
.
allowedOrientations (int) – A bitfield set of EMSCRIPTEN_ORIENTATION_xxx
flags.
EMSCRIPTEN_RESULT_SUCCESS
, or one of the other result values.
emscripten_unlock_orientation
(void)¶Removes the orientation lock so the screen can turn to any orientation.
EMSCRIPTEN_RESULT_SUCCESS
, or one of the other result values.
EMSCRIPTEN_EVENT_FULLSCREENCHANGE
¶Emscripten fullscreenchange event.
EMSCRIPTEN_FULLSCREEN_SCALE
¶An enum-like type which specifies how the Emscripten runtime should treat the CSS size of the target element when displaying it in fullscreen mode via calls to functions
emscripten_request_fullscreen_strategy()
and emscripten_enter_soft_fullscreen()
.
EMSCRIPTEN_FULLSCREEN_SCALE_DEFAULT
¶Specifies that the DOM element should not be resized by Emscripten runtime when transitioning between fullscreen and windowed modes. The browser will be responsible for scaling the DOM element to the fullscreen size. The proper browser behavior in this mode is to stretch the element to fit the full display ignoring aspect ratio, but at the time of writing, browsers implement different behavior here. See the discussion at https://github.com/emscripten-core/emscripten/issues/2556 for more information.
EMSCRIPTEN_FULLSCREEN_SCALE_STRETCH
¶Specifies that the Emscripten runtime should explicitly stretch the CSS size of the target element to cover the whole screen when transitioning to fullscreen mode. This will change the aspect ratio of the displayed content.
EMSCRIPTEN_FULLSCREEN_SCALE_ASPECT
¶Specifies that the Emscripten runtime should explicitly scale the CSS size of the target element to cover the whole screen, while adding either vertical or horizontal
black letterbox padding to preserve the aspect ratio of the content. The aspect ratio that is used here is the render target size of the canvas element. To change the
desired aspect ratio, call emscripten_set_canvas_element_size()
before entering fullscreen mode.
EMSCRIPTEN_FULLSCREEN_CANVAS_SCALE
¶An enum-like type which specifies how the Emscripten runtime should treat the pixel size (render target resolution) of the target canvas element when displaying it in
fullscreen mode via calls to functions emscripten_request_fullscreen_strategy()
and emscripten_enter_soft_fullscreen()
. To better understand the
underlying distinction between the CSS size of a canvas element versus the render target size of a canvas element, see https://www.khronos.org/webgl/wiki/HandlingHighDPI.
EMSCRIPTEN_FULLSCREEN_CANVAS_SCALE_NONE
¶Specifies that the Emscripten runtime should not do any changes to the render target resolution of the target canvas element that is displayed in fullscreen mode. Use this mode when your application is set up to render to a single fixed resolution that cannot be changed under any condition.
EMSCRIPTEN_FULLSCREEN_CANVAS_SCALE_STDDEF
¶Specifies that the Emscripten runtime should resize the render target of the canvas element to match 1:1 with the CSS size of the element in fullscreen mode. On high DPI
displays (window.devicePixelRatio > 1), the CSS size is not the same as the physical screen resolution of the device. Call emscripten_get_device_pixel_ratio()
to obtain the pixel ratio between CSS pixels and actual device pixels of the screen. Use this mode when you want to render to a pixel resolution that is DPI-independent.
EMSCRIPTEN_FULLSCREEN_CANVAS_SCALE_HIDEF
¶Specifies that the Emscripten runtime should resize the canvas render target size to match 1:1 with the physical screen resolution on the device. This corresponds to high definition displays on retina iOS and other mobile and desktop devices with high DPI. Use this mode to match and render 1:1 to the native display resolution.
EMSCRIPTEN_FULLSCREEN_FILTERING
¶An enum-like type that specifies what kind of image filtering algorithm to apply to the element when it is presented in fullscreen mode.
EMSCRIPTEN_FULLSCREEN_FILTERING_DEFAULT
¶Specifies that the image filtering mode should not be changed from the existing setting in the CSS style.
EMSCRIPTEN_FULLSCREEN_FILTERING_NEAREST
¶Applies a CSS style to the element that displays the content using a nearest-neighbor image filtering algorithm in fullscreen mode.
EMSCRIPTEN_FULLSCREEN_FILTERING_BILINEAR
¶Applies a CSS style to the element that displays the content using a bilinear image filtering algorithm in fullscreen mode. This is the default browser behavior.
EmscriptenFullscreenChangeEvent
¶The event structure passed in the fullscreenchange event.
isFullscreen
¶Specifies whether an element on the browser page is currently fullscreen.
fullscreenEnabled
¶Specifies if the current page has the ability to display elements fullscreen.
nodeName
¶The nodeName of the target HTML Element that is in full screen mode.
Maximum size 128 char
(i.e. EM_UTF8 nodeName[128]
).
If isFullscreen
is false
, then nodeName
, id
and elementWidth
and elementHeight
specify information about the element that just exited fullscreen mode.
id
¶The ID of the target HTML element that is in full screen mode.
Maximum size 128 char
(i.e. EM_UTF8 id[128]
).
EmscriptenFullscreenStrategy
¶The options structure that is passed in to functions emscripten_request_fullscreen_strategy()
and emscripten_enter_soft_fullscreen()
to configure how the target
element should be displayed in fullscreen mode.
scaleMode
¶Specifies the rule how the CSS size (the displayed size) of the target element is resized when displayed in fullscreen mode.
canvasResolutionScaleMode
¶Specifies how the render target size (the pixel resolution) of the target element is adjusted when displayed in fullscreen mode.
filteringMode
¶Specifies the image filtering algorithm to apply to the element in fullscreen mode.
canvasResizedCallback
¶If nonzero, points to a user-provided callback function which will be called whenever either the CSS or the canvas render target size changes. Use this callback to reliably obtain information about canvas resize events.
canvasResizedCallbackUserData
¶Stores a custom data field which will be passed to all calls to the user-provided callback function.
em_fullscreenchange_callback_func
¶Function pointer for the fullscreen event callback functions
, defined as:
typedef bool (*em_fullscreenchange_callback_func)(int eventType, const EmscriptenFullscreenChangeEvent *fullscreenChangeEvent, void *userData);
eventType (int) – The type of fullscreen event (EMSCRIPTEN_EVENT_FULLSCREENCHANGE
).
fullscreenChangeEvent (const EmscriptenFullscreenChangeEvent*) – Information about the fullscreen event that occurred.
userData (void*) – The userData
originally passed to the registration function.
true
(non zero) to indicate that the event was consumed by the callback handler.
bool
emscripten_set_fullscreenchange_callback
(const char *target, void *userData, bool useCapture, em_fullscreenchange_callback_func callback)¶Registers a callback function for receiving the fullscreenchange event.
target (const char*) – Target HTML element id.
userData (void*) – User-defined data to be passed to the callback (opaque to the API).
useCapture (bool) – Set true
to use capture.
callback (em_fullscreenchange_callback_func) – A callback function. The function is called with the type of event, information about the event, and user data passed from this registration function. The callback should return true
if the event is consumed.
EMSCRIPTEN_RESULT_SUCCESS
, or one of the other result values.
emscripten_get_fullscreen_status
(EmscriptenFullscreenChangeEvent *fullscreenStatus)¶Returns the current page fullscreen state.
fullscreenStatus (EmscriptenFullscreenChangeEvent*) – The most recently received fullscreen state.
EMSCRIPTEN_RESULT_SUCCESS
, or one of the other result values.
emscripten_request_fullscreen
(const char *target, bool deferUntilInEventHandler)¶Requests the given target element to transition to full screen mode.
Note
This function can be called anywhere, but for web security reasons its associated request can only be raised inside the event handler for a user-generated event (for example a key, mouse or touch press/release). This has implications for porting and the value of deferUntilInEventHandler
— see Functions affected by web security for more information.
Note
This function only performs a fullscreen request without changing any parameters of the DOM element that is to be displayed in fullscreen mode. At the time of writing, there are differences in how browsers present elements in fullscreen mode. For more information, read the discussion at https://github.com/emscripten-core/emscripten/issues/2556. To display an element in fullscreen mode in a way that is consistent across browsers, prefer calling the function emscripten_request_fullscreen_strategy()
instead. This function is best called only in scenarios where the preconfigured presets defined by emscripten_request_fullscreen_strategy()
conflict with the developer’s use case in some way.
target (const char*) – Target HTML element id.
deferUntilInEventHandler (bool) – If true
requests made outside of a user-generated event handler are automatically deferred until the user next presses a keyboard or mouse button. If false
the request will fail if called outside of a user-generated event handler.
EMSCRIPTEN_RESULT_SUCCESS
, or one of the other result values.
EMSCRIPTEN_RESULT
emscripten_request_fullscreen_strategy
(const char *target, bool deferUntilInEventHandler, const EmscriptenFullscreenStrategy *fullscreenStrategy)¶Requests the given target element to transition to full screen mode, using a custom presentation mode for the element. This function is otherwise the same as emscripten_request_fullscreen()
, but this function adds options to control how resizing and aspect ratio, and ensures that the behavior is consistent across browsers.
Note
This function makes changes to the DOM to satisfy consistent presentation across browsers. These changes have been designed to intrude as little as possible, and the changes are cleared once windowed browsing is restored. If any of these changes are conflicting, see the function emscripten_request_fullscreen()
instead, which performs a bare fullscreen request without any modifications to the DOM.
fullscreenStrategy (const EmscriptenFullscreenStrategy*) – [in] Points to a configuration structure filled by the caller which specifies display options for the fullscreen mode.
emscripten_exit_fullscreen
(void)¶Returns back to windowed browsing mode from a proper fullscreen mode.
Do not call this function to attempt to return to windowed browsing mode from a soft fullscreen mode, or vice versa.
EMSCRIPTEN_RESULT_SUCCESS
, or one of the other result values.
emscripten_enter_soft_fullscreen
(const char *target, const EmscriptenFullscreenStrategy *fullscreenStrategy)¶Enters a “soft” fullscreen mode, where the given target element is displayed in the whole client area of the page and all other elements are hidden, but does not actually request fullscreen mode for the browser. This function is useful in cases where the actual Fullscreen API is not desirable or needed, for example in packaged apps for Firefox OS, where applications essentially already cover the whole screen.
Pressing the esc button does not automatically exit the soft fullscreen mode. To return to windowed presentation mode, manually call the function emscripten_exit_soft_fullscreen()
.
emscripten_exit_soft_fullscreen
()¶Returns back to windowed browsing mode from a soft fullscreen mode. Do not call this function to attempt to return to windowed browsing mode from a real fullscreen mode, or vice versa.
EMSCRIPTEN_EVENT_POINTERLOCKCHANGE
¶Emscripten pointerlockchange event.
EMSCRIPTEN_EVENT_POINTERLOCKERROR
¶Emscripten pointerlockerror event.
EmscriptenPointerlockChangeEvent
¶The event structure passed in the pointerlockchange event.
isActive
¶Specifies whether an element on the browser page currently has pointer lock enabled.
em_pointerlockchange_callback_func
¶Function pointer for the pointerlockchange event callback functions
, defined as:
typedef bool (*em_pointerlockchange_callback_func)(int eventType, const EmscriptenPointerlockChangeEvent *pointerlockChangeEvent, void *userData);
eventType (int) – The type of pointerlockchange event (EMSCRIPTEN_EVENT_POINTERLOCKCHANGE
).
pointerlockChangeEvent (const EmscriptenPointerlockChangeEvent*) – Information about the pointerlockchange event that occurred.
userData (void*) – The userData
originally passed to the registration function.
true
(non zero) to indicate that the event was consumed by the callback handler.
bool
em_pointerlockerror_callback_func
¶Function pointer for the pointerlockerror event callback functions
, defined as:
typedef bool (*em_pointerlockerror_callback_func)(int eventType, const void *reserved, void *userData);
eventType (int) – The type of pointerlockerror event (EMSCRIPTEN_EVENT_POINTERLOCKERROR
).
void* reserved (const) – Reserved for future use; pass in 0.
userData (void*) – The userData
originally passed to the registration function.
true
(non zero) to indicate that the event was consumed by the callback handler.
bool
emscripten_set_pointerlockchange_callback
(const char *target, void *userData, bool useCapture, em_pointerlockchange_callback_func callback)¶Registers a callback function for receiving the pointerlockchange event.
Pointer lock hides the mouse cursor and exclusively gives the target element relative mouse movement events via the mousemove event.
target (const char*) – Target HTML element id.
userData (void*) – User-defined data to be passed to the callback (opaque to the API).
useCapture (bool) – Set true
to use capture.
callback (em_pointerlockchange_callback_func) – A callback function. The function is called with the type of event, information about the event, and user data passed from this registration function. The callback should return true
if the event is consumed.
EMSCRIPTEN_RESULT_SUCCESS
, or one of the other result values.
emscripten_set_pointerlockerror_callback
(const char *target, void *userData, bool useCapture, em_pointerlockerror_callback_func callback)¶Registers a callback function for receiving the pointerlockerror event.
target (const char*) – Target HTML element id.
userData (void*) – User-defined data to be passed to the callback (opaque to the API).
useCapture (bool) – Set true
to use capture.
callback (em_pointerlockerror_callback_func) – A callback function. The function is called with the type of event, information about the event, and user data passed from this registration function. The callback should return true
if the event is consumed.
EMSCRIPTEN_RESULT_SUCCESS
, or one of the other result values.
emscripten_get_pointerlock_status
(EmscriptenPointerlockChangeEvent *pointerlockStatus)¶Returns the current page pointerlock state.
pointerlockStatus (EmscriptenPointerlockChangeEvent*) – The most recently received pointerlock state.
EMSCRIPTEN_RESULT_SUCCESS
, or one of the other result values.
emscripten_request_pointerlock
(const char *target, bool deferUntilInEventHandler)¶Requests the given target element to grab pointerlock.
Note
This function can be called anywhere, but for web security reasons its associated request can only be raised inside the event handler for a user-generated event (for example a key, mouse or touch press/release). This has implications for porting and the value of deferUntilInEventHandler
— see Functions affected by web security for more information.
target (const char*) – Target HTML element id.
deferUntilInEventHandler (bool) – If true
requests made outside of a user-generated event handler are automatically deferred until the user next presses a keyboard or mouse button. If false
the request will fail if called outside of a user-generated event handler.
EMSCRIPTEN_RESULT_SUCCESS
, or one of the other result values.
emscripten_exit_pointerlock
(void)¶Exits pointer lock state and restores the mouse cursor to be visible again.
EMSCRIPTEN_RESULT_SUCCESS
, or one of the other result values.
EMSCRIPTEN_EVENT_VISIBILITYCHANGE
¶Emscripten visibilitychange event.
EmscriptenVisibilityChangeEvent
¶The event structure passed in the visibilitychange event.
If true, the current browser page is now hidden.
visibilityState
¶Specifies a more fine-grained state of the current page visibility status. One of the EMSCRIPTEN_VISIBILITY_
values.
em_visibilitychange_callback_func
¶Function pointer for the visibilitychange event callback functions
, defined as:
typedef bool (*em_visibilitychange_callback_func)(int eventType, const EmscriptenVisibilityChangeEvent *visibilityChangeEvent, void *userData);
eventType (int) – The type of visibilitychange
event (EMSCRIPTEN_VISIBILITY_HIDDEN
).
visibilityChangeEvent (const EmscriptenVisibilityChangeEvent*) – Information about the visibilitychange
event that occurred.
userData (void*) – The userData
originally passed to the registration function.
true
(non zero) to indicate that the event was consumed by the callback handler.
bool
emscripten_set_visibilitychange_callback
(void *userData, bool useCapture, em_visibilitychange_callback_func callback)¶Registers a callback function for receiving the visibilitychange event.
userData (void*) – User-defined data to be passed to the callback (opaque to the API).
useCapture (bool) – Set true
to use capture.
callback (em_visibilitychange_callback_func) – A callback function. The function is called with the type of event, information about the event, and user data passed from this registration function. The callback should return true
if the event is consumed.
EMSCRIPTEN_RESULT_SUCCESS
, or one of the other result values.
emscripten_get_visibility_status
(EmscriptenVisibilityChangeEvent *visibilityStatus)¶Returns the current page visibility state.
visibilityStatus (EmscriptenVisibilityChangeEvent*) – The most recently received page visibility state.
EMSCRIPTEN_RESULT_SUCCESS
, or one of the other result values.
EmscriptenTouchPoint
¶Specifies the status of a single touch point on the page.
identifier
¶An identification number for each touch point.
pageX
¶pageY
¶The touch coordinate relative to the viewport, in pixels, and including any scroll offset.
isChanged
¶Specifies whether the touch point changed during this event.
onTarget
¶Specifies whether this touch point is still above the original target on which it was initially pressed.
EmscriptenTouchEvent
¶Specifies the data of a single touchevent.
timestamp
¶Absolute wallclock time when the data was recorded (milliseconds).
numTouches
¶The number of valid elements in the touches array.
ctrlKey
¶shiftKey
¶altKey
¶metaKey
¶Specifies which modifiers were active during the touch event.
EmscriptenTouchPoint touches[32]
An array of currently active touches, one for each finger.
em_touch_callback_func
¶Function pointer for the touch event callback functions
, defined as:
typedef bool (*em_touch_callback_func)(int eventType, const EmscriptenTouchEvent *touchEvent, void *userData);
eventType (int) – The type of touch event (EMSCRIPTEN_EVENT_TOUCHSTART
).
touchEvent (const EmscriptenTouchEvent*) – Information about the touch event that occurred.
userData (void*) – The userData
originally passed to the registration function.
true
(non zero) to indicate that the event was consumed by the callback handler.
bool
emscripten_set_touchstart_callback
(const char *target, void *userData, bool useCapture, em_touch_callback_func callback)¶emscripten_set_touchend_callback
(const char *target, void *userData, bool useCapture, em_touch_callback_func callback)¶emscripten_set_touchmove_callback
(const char *target, void *userData, bool useCapture, em_touch_callback_func callback)¶emscripten_set_touchcancel_callback
(const char *target, void *userData, bool useCapture, em_touch_callback_func callback)¶Registers a callback function for receiving touch events : touchstart, touchend, touchmove and touchcancel.
target (const char*) – Target HTML element id.
userData (void*) – User-defined data to be passed to the callback (opaque to the API).
useCapture (bool) – Set true
to use capture.
callback (em_touch_callback_func) – A callback function. The function is called with the type of event, information about the event, and user data passed from this registration function. The callback should return true
if the event is consumed.
EMSCRIPTEN_RESULT_SUCCESS
, or one of the other result values.
EmscriptenGamepadEvent
¶Represents the current snapshot state of a gamepad.
timestamp
¶Absolute wallclock time when the data was recorded (milliseconds).
numAxes
¶The number of valid axis entries in the axis
array.
numButtons
¶The number of valid button entries in the analogButton and digitalButton arrays.
double axis[64]
The analog state of the gamepad axes, in the range [-1, 1].
double analogButton[64]
The analog state of the gamepad buttons, in the range [0, 1].
bool digitalButton[64]
The digital state of the gamepad buttons, either 0 or 1.
connected
¶Specifies whether this gamepad is connected to the browser page.
index
¶An ordinal associated with this gamepad, zero-based.
em_gamepad_callback_func
¶Function pointer for the gamepad event callback functions
, defined as:
typedef bool (*em_gamepad_callback_func)(int eventType, const EmscriptenGamepadEvent *gamepadEvent, void *userData)
eventType (int) – The type of gamepad event (EMSCRIPTEN_EVENT_GAMEPADCONNECTED
).
gamepadEvent (const EmscriptenGamepadEvent*) – Information about the gamepad event that occurred.
userData (void*) – The userData
originally passed to the registration function.
true
(non zero) to indicate that the event was consumed by the callback handler.
bool
emscripten_set_gamepadconnected_callback
(void *userData, bool useCapture, em_gamepad_callback_func callback)¶emscripten_set_gamepaddisconnected_callback
(void *userData, bool useCapture, em_gamepad_callback_func callback)¶Registers a callback function for receiving the gamepad events: gamepadconnected and gamepaddisconnected.
userData (void*) – User-defined data to be passed to the callback (opaque to the API).
useCapture (bool) – Set true
to use capture.
callback (em_gamepad_callback_func) – A callback function. The function is called with the type of event, information about the event, and user data passed from this registration function. The callback should return true
if the event is consumed.
EMSCRIPTEN_RESULT_SUCCESS
, or one of the other result values.
emscripten_sample_gamepad_data
(void)¶This function samples a new state of connected Gamepad data, and returns either EMSCRIPTEN_RESULT_SUCCESS if Gamepad API is supported by the current browser, or EMSCRIPTEN_RESULT_NOT_SUPPORTED if Gamepad API is not supported. Note that even if EMSCRIPTEN_RESULT_SUCCESS is returned, there may not be any gamepads connected yet to the current browser tab.
Call this function before calling either of the functions emscripten_get_num_gamepads() or emscripten_get_gamepad_status().
emscripten_get_num_gamepads
(void)¶After having called emscripten_sample_gamepad_data(), this function
returns the number of gamepads connected to the system or
EMSCRIPTEN_RESULT_NOT_SUPPORTED
if the current browser does not
support gamepads.
Note
A gamepad does not show up as connected until a button on it is pressed.
Note
Gamepad API uses an array of gamepad state objects to return the state of each device. The devices are identified via the index they are present in in this array. Because of that, if one first connects gamepad A, then gamepad B, and then disconnects gamepad A, the gamepad B shall not take the place of gamepad A, so in this scenario, this function will still keep returning two for the count of connected gamepads, even though gamepad A is no longer present. To find the actual number of connected gamepads, listen for the gamepadconnected and gamepaddisconnected events. Consider the return value of function emscripten_get_num_gamepads() minus one to be the largest index value that can be passed to the function emscripten_get_gamepad_status().
The number of gamepads connected to the browser tab.
int
emscripten_get_gamepad_status
(int index, EmscriptenGamepadEvent *gamepadState)¶After having called emscripten_sample_gamepad_data(), this function returns a snapshot of the current gamepad state for the gamepad controller located at given index of the controllers array.
index (int) – The index of the gamepad to check (in the array of connected gamepads).
gamepadState (EmscriptenGamepadEvent*) – The most recently received gamepad state.
EMSCRIPTEN_RESULT_SUCCESS
, or one of the other result values.
EMSCRIPTEN_EVENT_BATTERYCHARGINGCHANGE
¶EMSCRIPTEN_EVENT_BATTERYLEVELCHANGE
¶Emscripten batterymanager events.
EmscriptenBatteryEvent
¶The event structure passed in the batterymanager events: chargingchange
and levelchange
.
chargingTime
¶Time remaining until the battery is fully charged (seconds).
dischargingTime
¶Time remaining until the battery is empty and the system will be suspended (seconds).
level
¶Current battery level, on a scale of 0 to 1.0.
bool charging;
true
if the battery is charging, false
otherwise.
em_battery_callback_func
¶Function pointer for the batterymanager event callback functions
, defined as:
typedef bool (*em_battery_callback_func)(int eventType, const EmscriptenBatteryEvent *batteryEvent, void *userData);
eventType (int) – The type of batterymanager
event (EMSCRIPTEN_EVENT_BATTERYCHARGINGCHANGE
).
batteryEvent (const EmscriptenBatteryEvent*) – Information about the batterymanager
event that occurred.
userData (void*) – The userData
originally passed to the registration function.
true
(non zero) to indicate that the event was consumed by the callback handler.
bool
emscripten_set_batterychargingchange_callback
(void *userData, em_battery_callback_func callback)¶emscripten_set_batterylevelchange_callback
(void *userData, em_battery_callback_func callback)¶Registers a callback function for receiving the batterymanager events: chargingchange
and levelchange
.
userData (void*) – User-defined data to be passed to the callback (opaque to the API).
callback (em_battery_callback_func) – A callback function. The function is called with the type of event, information about the event, and user data passed from this registration function. The callback should return true
if the event is consumed.
EMSCRIPTEN_RESULT_SUCCESS
, or one of the other result values.
emscripten_get_battery_status
(EmscriptenBatteryEvent *batteryState)¶Returns the current battery status.
batteryState (EmscriptenBatteryEvent*) – The most recently received battery state.
EMSCRIPTEN_RESULT_SUCCESS
, or one of the other result values.
emscripten_vibrate
(int msecs)¶Produces a vibration for the specified time, in milliseconds.
msecs (int) – The amount of time for which the vibration is required (milliseconds).
EMSCRIPTEN_RESULT_SUCCESS
, or one of the other result values.
emscripten_vibrate_pattern
(int *msecsArray, int numEntries)¶Produces a complex vibration feedback pattern.
msecsArray (int*) – An array of timing entries [on, off, on, off, on, off, …] where every second one specifies a duration of vibration, and every other one specifies a duration of silence.
numEntries (int) – The number of integers in the array msecsArray
.
EMSCRIPTEN_RESULT_SUCCESS
, or one of the other result values.
EMSCRIPTEN_EVENT_BEFOREUNLOAD
¶Emscripten beforeunload event.
em_beforeunload_callback
¶Function pointer for the beforeunload event callback functions
, defined as:
typedef const char *(*em_beforeunload_callback)(int eventType, const void *reserved, void *userData);
eventType (int) – The type of beforeunload
event (EMSCRIPTEN_EVENT_BEFOREUNLOAD
).
reserved (const void*) – Reserved for future use; pass in 0.
userData (void*) – The userData
originally passed to the registration function.
Return a string to be displayed to the user.
char*
emscripten_set_beforeunload_callback
(void *userData, em_beforeunload_callback callback)¶Registers a callback function for receiving the page beforeunload event.
Hook into this event to perform actions immediately prior to page close (for example, to display a notification to ask if the user really wants to leave the page).
userData (void*) – User-defined data to be passed to the callback (opaque to the API).
callback (em_beforeunload_callback) – A callback function. The function is called with the type of event, information about the event, and user data passed from this registration function. The callback should return true
if the event is consumed.
EMSCRIPTEN_RESULT_SUCCESS
, or one of the other result values.
EMSCRIPTEN_EVENT_WEBGLCONTEXTLOST
¶EMSCRIPTEN_EVENT_WEBGLCONTEXTRESTORED
¶Emscripten WebGL context events.
EMSCRIPTEN_WEBGL_CONTEXT_HANDLE
¶Represents a handle to an Emscripten WebGL context object. The value 0 denotes an invalid/no context (this is a typedef to an intptr_t
).
EmscriptenWebGLContextAttributes
¶Specifies WebGL context creation parameters.
alpha
¶If true
, request an alpha channel for the context. If you create an alpha channel, you can blend the canvas rendering with the underlying web page contents. Default value: true
.
depth
¶If true
, request a depth buffer of at least 16 bits. If false
, no depth buffer will be initialized. Default value: true
.
stencil
¶If true
, request a stencil buffer of at least 8 bits. If false
, no stencil buffer will be initialized. Default value: false
.
antialias
¶If true
, antialiasing will be initialized with a browser-specified algorithm and quality level. If false
, antialiasing is disabled. Default value: true
.
premultipliedAlpha
¶If true
, the alpha channel of the rendering context will be treated as representing premultiplied alpha values. If false
, the alpha channel represents non-premultiplied alpha. Default value: true
.
preserveDrawingBuffer
¶If true
, the contents of the drawing buffer are preserved between consecutive requestAnimationFrame()
calls. If false
, color, depth and stencil are cleared at the beginning of each requestAnimationFrame()
. Generally setting this to false
gives better performance. Default value: false
.
powerPreference
¶Specifies a hint to the WebGL canvas implementation to how it should choose the use of available GPU resources. One of EM_WEBGL_POWER_PREFERENCE_DEFAULT, EM_WEBGL_POWER_PREFERENCE_LOW_POWER, EM_WEBGL_POWER_PREFERENCE_HIGH_PERFORMANCE.
failIfMajorPerformanceCaveat
¶If true
, requests context creation to abort if the browser is only able to create a context that does not give good hardware-accelerated performance. Default value: false
.
majorVersion
¶minorVersion
¶Emscripten-specific extensions which specify the WebGL context version to initialize.
For example, pass in majorVersion=1
, minorVersion=0
to request a WebGL 1.0 context, and majorVersion=2
, minorVersion=0
to request a WebGL 2.0 context.
Default value: majorVersion=1
, minorVersion=0
enableExtensionsByDefault
¶If true
, all GLES2-compatible non-performance-impacting WebGL extensions will automatically be enabled for you after the context has been created. If false
, no extensions are enabled by default, and you need to manually call emscripten_webgl_enable_extension()
to enable each extension that you want to use. Default value: true
.
explicitSwapControl
¶By default, when explicitSwapControl
is in its default state false
, rendered WebGL content is implicitly presented (displayed to the user) on the canvas when the event handler that renders with WebGL returns back to the browser event loop. If explicitSwapControl
is set to true
, rendered content will not be displayed on screen automatically when event handler function finishes, but the control of swapping is given to the user to manage, via the emscripten_webgl_commit_frame()
function.
In order to be able to set explicitSwapControl==true
, support for it must explicitly be enabled either 1) via adding the -sOFFSCREEN_FRAMEBUFFER
Emscripten linker flag, and enabling renderViaOffscreenBackBuffer==1
, or 2) via adding the linker flag -sOFFSCREENCANVAS_SUPPORT
, and running in a browser that supports OffscreenCanvas.
renderViaOffscreenBackBuffer
¶If true
, an extra intermediate backbuffer (offscreen render target) is allocated to the created WebGL context, and rendering occurs to this backbuffer instead of directly onto the WebGL “default backbuffer”. This is required to be enabled if 1) explicitSwapControl==true
and the browser does not support OffscreenCanvas, 2) when performing WebGL rendering in a worker thread and the browser does not support OffscreenCanvas, and 3) when performing WebGL context accesses from multiple threads simultaneously (independent of whether OffscreenCanvas is supported or not).
Because supporting offscreen framebuffer adds some amount of extra code to the compiled output, support for it must explicitly be enabled via the -sOFFSCREEN_FRAMEBUFFER
Emscripten linker flag. When building simultaneously with both -sOFFSCREEN_FRAMEBUFFER
and -sOFFSCREENCANVAS_SUPPORT
linker flags enabled, offscreen backbuffer can be used as a polyfill-like compatibility fallback to enable rendering WebGL from a pthread when the browser does not support the OffscreenCanvas API.
proxyContextToMainThread
¶This member specifies the threading model that will be used for the created WebGL context, when the WebGL context is created in a pthread. Three values are possible: EMSCRIPTEN_WEBGL_CONTEXT_PROXY_DISALLOW
, EMSCRIPTEN_WEBGL_CONTEXT_PROXY_FALLBACK
or EMSCRIPTEN_WEBGL_CONTEXT_PROXY_ALWAYS
. If EMSCRIPTEN_WEBGL_CONTEXT_PROXY_DISALLOW
is specified, the WebGLRenderingContext object will be created inside the pthread that is calling the emscripten_webgl_create_context()
function as an OffscreenCanvas-based rendering context. This is only possible if 1) current browser supports OffscreenCanvas specification, 2) code was compiled with -sOFFSCREENCANVAS_SUPPORT
linker flag enabled, 3) the Canvas object that the context is being created on was transferred over to the calling pthread with function emscripten_pthread_attr_settransferredcanvases()
when the pthread was originally created, and 4) no OffscreenCanvas-based context already exists from the given Canvas at the same time.
If a WebGL rendering context is created as an OffscreenCanvas-based context, it will have the limitation that only the pthread that created the context can enable access to it (via emscripten_webgl_make_context_current()
function). Other threads will not be able to activate rendering to the context, i.e. OffscreenCanvas-based contexts are essentially “pinned” to the pthread that created them.
If the current browser does not support OffscreenCanvas, you can specify the EMSCRIPTEN_WEBGL_CONTEXT_PROXY_ALWAYS
WebGL context creation flag. If this flag is passed, and code was compiled with -sOFFSCREEN_FRAMEBUFFER
enabled, the WebGL context will be created as a “proxied context”. In this context mode, the WebGLRenderingContext object will actually be created on the main browser thread, and all WebGL API calls will be proxied as asynchronous messages from the pthread into the main thread. This will have a performance and latency impact in comparison to OffscreenCanvas contexts, however unlike OffscreenCanvas-based contexts, proxied contexts can be shared across any number of pthreads: you can use the emscripten_webgl_make_context_current()
function in any pthread to activate and deactivate access to the WebGL context: for example, you could have one WebGL loading thread, and another WebGL rendering thread that coordinate shared access to the WebGL rendering context by cooperatively acquiring and releasing access to the WebGL rendering context via the emscripten_webgl_make_context_current()
function. Proxied contexts do not require any special support from the browser, so any WebGL capable browser can create a proxied WebGL context.
The EMSCRIPTEN_WEBGL_CONTEXT_PROXY_ALWAYS
WebGL context creation flag will always create a proxied context, even if the browser did support OffscreenCanvas. If you would like to prefer to create a higher performance OffscreenCanvas context whenever supported by the browser, but only fall back to a proxied WebGL context to keep compatibility with browsers that do not yet have OffscreenCanvas support, you can specify the EMSCRIPTEN_WEBGL_CONTEXT_PROXY_FALLBACK
context creation flag. In order to use this flag, code should be compiled with both -sOFFSCREEN_FRAMEBUFFER
and -sOFFSCREENCANVAS_SUPPORT
linker flags.
Default value of proxyContextToMainThread
after calling emscripten_webgl_init_context_attributes()
is EMSCRIPTEN_WEBGL_CONTEXT_PROXY_DISALLOW
, if the WebGL context is being created on the main thread. This means that by default WebGL contexts created on the main thread are not shareable between multiple threads (to avoid accidental performance loss from enabling proxying when/if it is not needed). To create a context that can be shared between multiple pthreads, set the proxyContextToMainThread
flag EMSCRIPTEN_WEBGL_CONTEXT_PROXY_ALWAYS
.
em_webgl_context_callback
¶Function pointer for the WebGL Context event callback functions
, defined as:
typedef bool (*em_webgl_context_callback)(int eventType, const void *reserved, void *userData);
eventType (int) – The type of WebGL context event
.
reserved (const void*) – Reserved for future use; pass in 0.
userData (void*) – The userData
originally passed to the registration function.
true
(non zero) to indicate that the event was consumed by the callback handler.
bool
emscripten_set_webglcontextlost_callback
(const char *target, void *userData, bool useCapture, em_webgl_context_callback callback)¶emscripten_set_webglcontextrestored_callback
(const char *target, void *userData, bool useCapture, em_webgl_context_callback callback)¶Registers a callback function for the canvas WebGL context events: webglcontextlost
and webglcontextrestored
.
target (const char*) – Target HTML element id.
userData (void*) – User-defined data to be passed to the callback (opaque to the API).
useCapture (bool) – Set true
to use capture.
callback (em_webgl_context_callback) – A callback function. The function is called with the type of event, information about the event, and user data passed from this registration function. The callback should return true
if the event is consumed.
EMSCRIPTEN_RESULT_SUCCESS
, or one of the other result values.
emscripten_is_webgl_context_lost
(EMSCRIPTEN_WEBGL_CONTEXT_HANDLE context)¶Queries the given WebGL context if it is in a lost context state.
target (EMSCRIPTEN_WEBGL_CONTEXT_HANDLE) – Specifies a handle to the context to test.
true
if the WebGL context is in a lost state (or the context does not exist)
bool
emscripten_webgl_init_context_attributes
(EmscriptenWebGLContextAttributes *attributes)¶Populates all fields of the given EmscriptenWebGLContextAttributes
structure to their default values for use with WebGL 1.0.
Call this function as a forward-compatible way to ensure that if there are new fields added to the EmscriptenWebGLContextAttributes
structure in the future, that they also will get default-initialized without having to change any code.
attributes (EmscriptenWebGLContextAttributes*) – The structure to be populated.
emscripten_webgl_create_context
(const char *target, const EmscriptenWebGLContextAttributes *attributes)¶Creates and returns a new WebGL context.
Note
A successful call to this function will not immediately make that rendering context active. Call emscripten_webgl_make_context_current()
after creating a context to activate it.
This function will try to initialize the context version that was exactly requested. It will not e.g. initialize a newer backwards-compatible version or similar.
target (const char*) – The DOM canvas element in which to initialize the WebGL context.
attributes (const EmscriptenWebGLContextAttributes*) – The attributes of the requested context version.
On success, a non-zero value that represents a handle to the created context. On failure, 0.
emscripten_webgl_make_context_current
(EMSCRIPTEN_WEBGL_CONTEXT_HANDLE context)¶Activates the given WebGL context for rendering. After calling this function, all OpenGL functions (glBindBuffer()
, glDrawArrays()
, etc.) can be applied to the given GL context.
context (EMSCRIPTEN_WEBGL_CONTEXT_HANDLE) – The WebGL context to activate.
EMSCRIPTEN_RESULT_SUCCESS
, or one of the other result values.
emscripten_webgl_get_current_context
()¶Returns the currently active WebGL rendering context, or 0 if no context is active. Calling any WebGL functions when there is no active rendering context is undefined and may throw a JavaScript exception.
The currently active WebGL rendering context, or 0 if no context is active.
emscripten_webgl_get_context_attributes
(EMSCRIPTEN_WEBGL_CONTEXT_HANDLE context, EmscriptenWebGLContextAttributes *outAttributes)¶Fetches the context creation attributes that were used to initialize the given WebGL context.
context (EMSCRIPTEN_WEBGL_CONTEXT_HANDLE) – The WebGL context to query.
*outAttributes (EmscriptenWebGLContextAttributes) – The context creation attributes of the specified context will be filled in here. This pointer cannot be null.
On success, EMSCRIPTEN_RESULT_SUCCESS.
emscripten_webgl_commit_frame
()¶Presents (“swaps”) the content rendered on the currently active WebGL context to be visible on the canvas. This function is available on WebGL contexts that were created with the explicitSwapControl==true
context creation attribute. If explicitSwapControl==false
, then the rendered content is displayed on the screen “implicitly” when yielding back to the browser from the calling event handler.
EMSCRIPTEN_RESULT_SUCCESS
, or one of the other result values, denoting a reason for failure.
emscripten_webgl_get_drawing_buffer_size
(EMSCRIPTEN_WEBGL_CONTEXT_HANDLE context, int *width, int *height)¶Gets the drawingBufferWidth
and drawingBufferHeight
of the specified WebGL context.
context (EMSCRIPTEN_WEBGL_CONTEXT_HANDLE) – The WebGL context to get width/height of.
*width (int) – The context’s drawingBufferWidth
.
*height (int) – The context’s drawingBufferHeight
.
EMSCRIPTEN_RESULT_SUCCESS
, or one of the other result values.
emscripten_webgl_destroy_context
(EMSCRIPTEN_WEBGL_CONTEXT_HANDLE context)¶Deletes the given WebGL context. If that context was active, then the no context is set to active.
context (EMSCRIPTEN_WEBGL_CONTEXT_HANDLE) – The WebGL context to delete.
EMSCRIPTEN_RESULT_SUCCESS
, or one of the other result values.
emscripten_webgl_enable_extension
(EMSCRIPTEN_WEBGL_CONTEXT_HANDLE context, const char *extension)¶Enables the given extension on the given context.
context (EMSCRIPTEN_WEBGL_CONTEXT_HANDLE) – The WebGL context on which the extension is to be enabled.
extension (const char*) – A string identifying the WebGL extension. For example “OES_texture_float”.
true if the given extension is supported by the context, and false if the extension was not available.
bool
emscripten_set_canvas_element_size
(const char *target, int width, int height)¶Resizes the pixel width and height of the given Canvas element in the DOM.
target – Specifies a selector for the canvas to resize.
width – New pixel width of canvas element.
height – New pixel height of canvas element.
EMSCRIPTEN_RESULT_SUCCESS if resizing succeeded, and one of the EMSCRIPTEN_RESULT_* error values on failure.
emscripten_get_canvas_element_size
(const char *target, int *width, int *height)¶Gets the current pixel width and height of the given Canvas element in the DOM.
target – Specifies a selector for the canvas to resize.
width – A pointer to memory location where the width of the canvas element is received. This pointer may not be null.
height – A pointer to memory location where the height of the canvas element is received. This pointer may not be null.
EMSCRIPTEN_RESULT_SUCCESS if width and height retrieval succeeded, and one of the EMSCRIPTEN_RESULT_* error values on failure.
emscripten_set_element_css_size
(const char * target, double width, double height)¶Resizes the CSS width and height of the element specified by target
on the Emscripten web page.
target (const char*) – Element to resize.
width (double) – New width of the element.
height (double) – New height of the element.
EMSCRIPTEN_RESULT_SUCCESS
, or one of the other result values.
emscripten_get_element_css_size
(const char * target, double * width, double * height)¶Gets the current CSS width and height of the element specified by target
.
target (const char*) – Element to get size of.
width (double*) – Width of the element.
height (double*) – Height of the element.
EMSCRIPTEN_RESULT_SUCCESS
, or one of the other result values.
The API provided here are low-level functions that directly call the relevant Web APIs and nothing more. They don’t integrate with the emscripten runtime, such as checking if the program has halted and cancelling a callback if so. For that purpose,
see the function emscripten_set_main_loop()
.
emscripten_set_timeout
(void (*cb)(void *userData), double msecs, void *userData)¶Performs a setTimeout()
callback call on the given function on the calling thread.
cb – The callback function to call.
msecs – Millisecond delay until the callback should fire.
userData – Specifies a pointer sized field of custom data that will be passed in to the callback function.
An ID to the setTimeout()
call that can be passed to emscripten_clear_timeout()
to cancel the pending timeout timer.
emscripten_clear_timeout
(long setTimeoutId)¶Cancels a pending setTimeout()
call on the calling thread. This function must be called on the same
thread as the emscripten_set_timeout()
call that registered the callback.
setTimeoutId – An ID returned by function emscripten_set_timeout()
.
emscripten_set_timeout_loop
(bool (*cb)(double time, void *userData), double intervalMsecs, void *userData)¶Initializes a setTimeout()
loop on the given function on the calling thread. The specified callback
function ‘cb’ needs to keep returning true
as long as the animation loop should continue to run.
When the function returns false, the setTimeout()
loop will stop.
Note: The loop will start immediately with a 0 msecs delay - the passed in intervalMsecs time specifies
the interval that the consecutive callback calls should fire at.
cb – The callback function to call.
intervalMsecs – Millisecond interval at which the callback should keep firing.
userData – Specifies a pointer sized field of custom data that will be passed in to the callback function.
emscripten_request_animation_frame
(bool (*cb)(double time, void *userData), void *userData)¶Performs a single requestAnimationFrame()
callback call on the given function on the calling thread.
cb – The callback function to call. This function will receive the current high precision timer value
(value of performance.now()
) at the time of the call.
userData – Specifies a pointer sized field of custom data that will be passed in to the callback function.
An ID to the requestAnimationFrame()
call that can be passed to
emscripten_cancel_animation_frame()
to
cancel the pending requestAnimationFrame
timer.
emscripten_cancel_animation_frame
(long requestAnimationFrameId)¶Cancels a registered requestAnimationFrame()
callback on the calling thread before it is run. This
function must be called on the same thread as the emscripten_request_animation_frame()
call that
registered the callback.
requestAnimationFrameId – An ID returned by function emscripten_request_animation_frame()
.
emscripten_request_animation_frame_loop
(bool (*cb)(double time, void *userData), void *userData)¶Initializes a requestAnimationFrame()
loop on the given function on the calling thread. The specified
callback function ‘cb’ needs to keep returning true
as long as the animation loop should continue
to run. When the function returns false, the animation frame loop will stop.
cb – The callback function to call. This function will receive the current high precision timer value
(value of performance.now()
) at the time of the call.
userData – Specifies a pointer sized field of custom data that will be passed in to the callback function.
emscripten_set_immediate
(void (*cb)(void *userData), void *userData)¶Performs a setImmediate()
callback call on the given function on the calling thread. Returns an ID
to the setImmediate()
call that can be passed to emscripten_clear_immediate()
function to cancel
a pending setImmediate()
invocation.
TODO: Currently the polyfill of setImmediate()
only works in the main browser thread, but not in pthreads.
cb – The callback function to call.
userData – Specifies a pointer sized field of custom data that will be passed in to the callback function.
An ID to the setImmediate()
call that can be passed to emscripten_clear_immediate()
to cancel the pending callback.
emscripten_clear_immediate
(long setImmediateId)¶Cancels a pending setImmediate()
call on the calling thread. This function must be called on the same
thread as the emscripten_set_immediate()
call that registered the callback.
setImmediateId – An ID returned by function emscripten_set_immediate()
.
emscripten_set_immediate_loop
(bool (*cb)(void *userData), void *userData)¶Initializes a setImmediate()
loop on the given function on the calling thread. The specified callback
function ‘cb’ needs to keep returning true
as long as the loop should continue to run.
When the function returns false, the setImmediate()
loop will stop.
TODO: Currently the polyfill of setImmediate()
only works in the main browser thread, but not in pthreads.
cb – The callback function to call.
userData – Specifies a pointer sized field of custom data that will be passed in to the callback function.
emscripten_set_interval
(void (*cb)(void *userData), double intervalMsecs, void *userData)¶Initializes a setInterval()
loop on the given function on the calling thread. Returns an ID to the
initialized loop. Call emscripten_clear_interval()
with this ID to terminate the loop.
Note that this function will cause the given callback to be called repeatedly. Do not call
emscripten_set_interval()
again on the same callback function from inside the callback, as that would
register multiple loops to run simultaneously.
cb – The callback function to call.
intervalMsecs – Millisecond interval at which the callback should keep firing.
userData – Specifies a pointer sized field of custom data that will be passed in to the callback function.
An ID to the setInterval() call that can be passed to emscripten_clear_interval() to cancel the currently executing interval timer.
emscripten_clear_interval
(long setIntervalId)¶Cancels a currently executing setInterval()
loop on the calling thread. This function must be called on
the same thread as the emscripten_set_interval()
call that registered the callback.
setIntervalId – An ID returned by function emscripten_set_interval()
.
emscripten_date_now
(void)¶Calls JavaScript Date.now()
function in the current thread.
The number of msecs elapsed since the UNIX epoch. (00:00:00 Thursday, 1 January 1970)
emscripten_performance_now
(void)¶Calls JavaScript performance.now()
function in the current thread. Note that the returned value of
this function is based on different time offset depending on which thread this function is called in.
That is, do not compare absolute time values returned by performance.now() across threads. (comparing
relative timing values is ok). On the main thread this function returns the number of milliseconds elapsed
since page startup time. In a Web Worker/pthread, this function returns the number of milliseconds since
the Worker hosting that pthread started up. (Workers are generally not torn down when a pthread quits and
a second one starts, but they are kept alive in a pool, so this function is not guaranteed to start
counting time from 0 at the time when a pthread starts)
A high precision wallclock time value in msecs.
emscripten_throw_number
(double number)¶Invokes JavaScript throw statement and throws a number.
emscripten_throw_string
(const char *utf8String)¶Invokes JavaScript throw statement and throws a string.
emscripten_unwind_to_js_event_loop
(void)¶Throws a JavaScript exception that unwinds the stack and yields execution back to the browser event loop. This function does not return execution back to calling code.
This function can be useful when porting code that would enter an infinite loop. Instead of
actually running an infinite loop, which is not allowed on the Web, we can set up the body of
the loop to execute asynchronously (using emscripten_set_main_loop()
or something else), and call
this function to halt execution, which is important as we do not want execution to continue
normally.