Canvas
A Canvas manages a Scene's HTML canvas and its WebGL context.
Overview
- Each Scene provides a Canvas as a read-only property on itself.
- When a Scene is configured with the ID of an existing HTMLCanvasElement, then the Canvas will bind to that, otherwise the Canvas will automatically create its own.
- A Canvas will fire a boundary event whenever the HTMLCanvasElement resizes.
- A Canvas is responsible for obtaining a WebGL context from the HTMLCanvasElement.
- A Canvas also fires a Canvas/webglContextLost:event event when the WebGL context is lost, and a webglContextRestored when it is restored again.
- The various components within the parent Scene will transparently recover on the webglContextRestored event.
A Canvas also has
- a Progress, which shows a busy progress when a Model is loading, or when directed by application logic, and
Examples
- Multiple canvases/scenes in a page
- Taking canvas snapshots
- Transparent canvas with background image
- Canvas with multiple viewports
Usage
In the example below, we're creating a Scene without specifying an HTML canvas element for it. This causes the Scene's Canvas component to create its own default element within the page. Then we subscribe to various events fired by that Canvas component.
var scene = new xeogl.Scene();
// Get the Canvas off the Scene
// Since we did not configure the Scene with the ID of a DOM canvas element,
// the Canvas will create its own canvas element in the DOM
var canvas = scene.canvas;
// Get the WebGL context off the Canvas
var gl = canvas.gl;
// Subscribe to Canvas size updates
canvas.on("boundary", function(boundary) {
//...
});
// Subscribe to WebGL context loss events on the Canvas
canvas.on("webglContextLost", function() {
//...
});
// Subscribe to WebGL context restored events on the Canvas
canvas.on("webglContextRestored", function(gl) {
var newContext = gl;
//...
});When we want to bind the Canvas to an existing HTML canvas element, configure the Scene with the ID of the element, like this:
// Create a Scene, this time configuring it with the
// ID of an existing DOM canvas element
var scene = new xeogl.Scene({
canvasId: "myCanvas"
});
// ..and the rest of this example can be the same as the previous example.The Scene will attempt to get use WebGL 2, or fall back on WebGL 1 if that's absent. If you just want WebGL 1, disable WebGL 2 like so:
var scene = new xeogl.Scene({
canvasId: "myCanvas",
webgl2 : true
});
// ..and the rest of this example can be the same as the previous examples.Index
Properties
Methods
create
-
[cfg]
Convenience method for creating a Component within this Component's Scene.
The method is given a component configuration, like so:
var material = myComponent.create({
type: "xeogl.PhongMaterial",
diffuse: [1,0,0],
specular: [1,1,0]
}, "myMaterial");Parameters:
-
[cfg]optionalConfiguration for the component instance.
Returns:
destroy
()
Destroys this component.
Fires a destroyed event on this Component.
Automatically disassociates this component from other components, causing them to fall back on any defaults that this component overrode on them.
TODO: describe effect with respect to #create
error
-
message
Logs an error for this component to the JavaScript console.
The console message will have this format: [ERROR] [<component type> =<component id>: <message>
Also fires the message as an error event on the parent Scene.
Parameters:
-
messageStringThe message to log
fire
-
event -
value -
[forget=false]
Fires an event on this component.
Notifies existing subscribers to the event, optionally retains the event to give to any subsequent notifications on the event as they are made.
Parameters:
-
eventStringThe event type name
-
valueObjectThe event parameters
-
[forget=false]Boolean optionalWhen true, does not retain for subsequent subscribers
getSnapshot
-
[params] -
[ok]
Returns a snapshot of this Canvas as a Base64-encoded image.
When a callback is given, this method will capture the snapshot asynchronously, on the next animation frame, and return it via the callback.
When no callback is given, this method captures and returns the snapshot immediately. Note that is only possible when you have configured the Canvas's Scene to preserve the WebGL drawing buffer, which has a performance overhead.
Usage:
// Get snapshot asynchronously
myScene.canvas.getSnapshot({
width: 500, // Defaults to size of canvas
height: 500,
format: "png" // Options are "jpeg" (default), "png" and "bmp"
}, function(imageDataURL) {
imageElement.src = imageDataURL;
});
// Get snapshot synchronously, requires that Scene be
// configured with preserveDrawingBuffer; true
imageElement.src = myScene.canvas.getSnapshot({
width: 500,
height: 500,
format: "png"
});Parameters:
-
[params]optionalCapture options.
-
[width]Number optionalDesired width of result in pixels - defaults to width of canvas.
-
[height]Number optionalDesired height of result in pixels - defaults to height of canvas.
-
[format="jpeg"]String optionalDesired format; "jpeg", "png" or "bmp".
-
-
[ok]Function optionalCallback to return the image data when taking a snapshot asynchronously.
Returns:
String-encoded image data when taking the snapshot synchronously. Returns null when the ok callback is given.
hasSubs
-
event
Returns true if there are any subscribers to the given event on this component.
Parameters:
-
eventStringThe event
Returns:
True if there are any subscribers to the given event on this component.
isType
-
type
Tests if this component is of the given type, or is a subclass of the given type.
The type may be given as either a string or a component constructor.
This method works by walking up the inheritance type chain, which this component provides in property Component/superTypes:property, returning true as soon as one of the type strings in the chain matches the given type, of false if none match.
Examples:
var myRotate = new xeogl.Rotate({ ... });
myRotate.isType(xeogl.Component); // Returns true for all xeogl components
myRotate.isType("xeogl.Component"); // Returns true for all xeogl components
myRotate.isType(xeogl.Rotate); // Returns true
myRotate.isType(xeogl.Transform); // Returns true
myRotate.isType("xeogl.Transform"); // Returns true
myRotate.isType(xeogl.Mesh); // Returns false, because xeogl.Rotate does not (even indirectly) extend xeogl.MeshParameters:
-
typeString | FunctionComponent type to compare with, eg "xeogl.PhongMaterial", or a xeogl component constructor.
Returns:
True if this component is of given type or is subclass of the given type.
log
-
message
Logs a console debugging message for this component.
The console message will have this format: [LOG] [<component type> <component id>: <message>
Parameters:
-
messageStringThe message to log
off
-
subId
Cancels an event subscription that was previously made with Component#on() or Component#once().
Parameters:
-
subIdStringPublication subId
on
-
event -
callback -
[scope=this]
Subscribes to an event on this component.
The callback is be called with this component as scope.
Parameters:
-
eventStringThe event
-
callbackFunctionCalled fired on the event
-
[scope=this]Object optionalScope for the callback
Returns:
Handle to the subscription, which may be used to unsubscribe with {@link #off}.
once
-
event -
callback -
[scope=this]
Subscribes to the next occurrence of the given event, then un-subscribes as soon as the event is subIdd.
This is equivalent to calling Component#on(), and then calling Component#off() inside the callback function.
Parameters:
-
eventStringData event to listen to
-
callbackFunction(data)Called when fresh data is available at the event
-
[scope=this]Object optionalScope for the callback
Properties
backgroundColor
Float32Array
A background color for the canvas. This is overridden by backgroundImage.
You can set this to a new color at any time.
Default: null
backgroundImage
String
URL of a background image for the canvas. This is overrided by Canvas/backgroundColor/property.
You can set this to a new file path at any time.
boundary
Array of Number
final
Boundary of the Canvas in absolute browser window coordinates.
Usage:
var boundary = myScene.canvas.boundary;
var xmin = boundary[0];
var ymin = boundary[1];
var width = boundary[2];
var height = boundary[3];canvas
HTMLCanvasElement
final
The HTML canvas. When the Viewer was configured with the ID of an existing canvas within the DOM, then this property will be that element, otherwise it will be a full-page canvas that this Canvas has created by default, with a z-index of -10000.
destroyed
Boolean
True as soon as this Component has been destroyed
gl
WebGLRenderingContext
final
The WebGL rendering context.
model
Model
final
The Model which contains this Component, if any.
Will be null if this Component is not in a Model.
transparent
Boolean
final
Indicates whether this Canvas is transparent.
Default: {false}
type
String
final
JavaScript class name for this Component.
For example: "xeogl.AmbientLight", "xeogl.MetallicMaterial" etc.
webgl2
Boolean
final
True when WebGL 2 support is enabled.
Events
boundary
Fired whenever this Canvas's boundary property changes.
Event Payload:
-
valueObjectThe property's new value
destroyed
Fired when this Component is destroyed.
webglContextFailed
Fired whenever the canvas failed to get a WebGL context, which probably means that WebGL is either unsupported or has been disabled.
webglcontextlost
Fired whenever the WebGL context has been lost
webglContextRestored
Fired whenever the WebGL context has been restored again after having previously being lost
Event Payload:
-
valueObjectThe WebGL context object