AnimationLoop

Manages an animation loop and optionally a WebGL context and a WebGL canvas. It provides a number of features related to initialization and animation of a WebGL context.

• Provides a number of commonly needed variables as part of the context object which is passed to onRender and onFinalize callbacks.
• Objects returned by onInitialize will be appended to context object hence available to onRender and onFinalize.
• To avoid problems with page load timing, move context creation to the onCreateContext method.
• By default, onRender method manages resizing of canvas, viewport and framebuffer.
• Makes it easy to wait for the HTML page to load before creating a canvas and WebGL resources.

References:

• WebGL Fundamentals contains excellent information on the subtleties of the how the WebGL context's drawing buffer and the HTML canvas interact.
• When running in the browser, this class uses requestAnimationFrame

Usage

Autocreates a canvas/context

import {AnimationLoop, ClipSpace} from '@luma.gl/engine';

const animationLoop = new AnimationLoop({
  onInitialize({gl}) {
    // Keys in the object returned here will be available in onRender
    return {
      clipSpaceQuad: new ClipSpace({gl, fs: FRAGMENT_SHADER})
    };
  },
  onRender({tick, clipSpaceQuad}) {
    // Tick is autoupdated by AnimationLoop
    clipSpaceQuad.setUniforms({uTime: tick * 0.01}).draw();
  }
});

animationLoop.start();

Use a canvas in the existing DOM through its HTML id

animationLoop.start({canvas: 'my-canvas'});

Methods

constructor(props : Object)

new AnimationLoop({
  onCreateContext,
  onInitialize,
  onFinalize,
  onRender,

  autoResizeViewport,
  autoResizeDrawingBuffer
});

• props.onCreateContext=null (callback) - function without parameters that returns a WebGLRenderingContext. This callback will be called exactly once, after page load completes.
• props.onInitialize (callback) - if supplied, will be called once after first start() has been called, after page load completes and a context has been created.
• props.onRender=null (callback) - Called on every animation frame.
• props.onFinalize=null (callback) - Called once when animation is stopped. Can be used to delete objects or free any resources created during onInitialize.
• props.onError=null (callback) - Called when an error is about to be thrown.
• props.autoResizeViewport=true - If true, calls gl.viewport(0, 0, gl.drawingBufferWidth, gl.drawingBufferHeight) each frame before onRender is called. Set to false to control viewport size.
• props.autoResizeDrawingBuffer=true - If true, checks the canvas size every frame and updates the drawing buffer size if needed.
• props.useDevicePixels - Whether to use window.devicePixelRatio as a multiplier, e.g. in autoResizeDrawingBuffer etc. Refer to Experimental API section below for more use cases of this prop.
• props.gl=null (WebGLContext) - If supplied, will render into this external context instead of creating a new one.
• props.glOptions={} (object) - Options to create the WebGLContext with. See createGLContext.
• props.debug=false (bool) - Enable debug mode will provide more validations and error messages, but less performant.
• props.createFramebuffer=false (bool) - If true, will make a framebuffer (FrameBuffer) parameter available to onInitialize and onRender callbacks.

start([options : Object]) : AnimationLoop

Restarts the animation

animationLoop.start(options)

• options={} (object) - Options to create the WebGLContext with. See createGLContext.

stop() : AnimationLoop

Stops the animation

animationLoop.stop()

waitForRender() : Promise

Returns a promise which resolves in the next frame after rendering and the onRender callback have completed.

const loop = await animationLoop.waitForRender()
// can now read pixels from webgl context
loop.gl.readPixels(...)

redraw() : AnimationLoop

Immediately invokes a redraw (call onRender with updated animation props). Only use if the canvas must be updated synchronously.

setNeedsRedraw(reason : String) : AnimationLoop

animationLoop.setNeedsRedraw(reason)

• reason (String) - A human readable string giving a hint as to why redraw was needed (e.g. "geometry changed").

If set, the value will be provided as the needsRedraw field to the onRender callback.

Notes:

• onRender will be called for each animation frame regardless of whether this flag is set, and the redraw reason is automatically cleared.
• If called multiple times, the reason provided in the first call will be remembered.
• AnimationLoop automatically sets this flag if the WebGL context's drawing buffer size changes.

setProps(props : Object) : AnimationLoop

animationLoop.setProps({...props})

• props.autoResizeViewport - Call gl.viewport before each call to onRender()
• props.autoResizeDrawingBuffer - Update the drawing buffer size to match the canvas size before each call to onRender()
• props.useDevicePixels - Whether to use window.devicePixelRatio as a multiplier, e.g. in autoResizeDrawingBuffer etc.

attachTimeline(timeline: Timeline)

Attach an Timeline object to the animation loop. Allows time produced for animations to be paused, played, etc. See Timeline documentation for more info.

detachTimeline()

Detach the currently attached timeline from the animation loop.

toDataURL

Returns returns a Promise that resolves to the data URL of the canvas once drawing operations are complete for the current frame. The data URL can be used as the src for an HTML image element.

animationLoop.toDataURL()

isContextLost()

Returns the current state of the WebGL context used by the animation loop.

Callback Parameters

The callbacks onInitialize, onRender and onFinalize that the app supplies to the AnimationLoop, will be called with an object containing named parameters:

Frame timers

• The animation loop tracks GPU and CPU render time of each frame the in member properties cpuTime and gpuTime. If gpuTime is set to -1, then the timing for the last frame was invalid and should not be used (this rare and might occur, for example, if the GPU was throttled mid-frame).

Experimental API (useDevicePixels)

useDevicePixels can accept a custom ratio (Number), instead of true or false. This allows rendering to a much smaller or higher resolutions. When using high value (usually more than device pixel ratio), it is possible it can get clamped down, this happens due to system memory limitation, in such cases a warning will be logged to the browser console. For additional details check device pixels document.

Remarks

• You can instantiate multiple AnimationLoop classes in parallel, rendering into the same or different WebGLRenderingContexts.
• Works both in browser and under Node.js.
• All AnimationLoop methods can be chained.
• Postpones context creation until the page (i.e. all HTML) has been loaded. At this time it is safe to specify canvas ids when calling createGLContext.
• The supplied callback function must return a WebGLRenderingContext or an error will be thrown.
• This callback registration function should not be called if a WebGLRenderingContext was supplied to the AnimationLoop constructor.