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<html>
<head>
<meta charset='utf-8'>
<meta name='viewport' content='width=device-width, initial-scale=1, user-scalable=no'>
<meta name='mobile-web-app-capable' content='yes'>
<meta name='apple-mobile-web-app-capable' content='yes'>
<!-- Origin Trial Token, feature = WebXR Device API, origin = https://immersive-web.github.io, expires = 2018-08-28 -->
<meta http-equiv="origin-trial" data-feature="WebXR Device API" data-expires="2018-08-28" content="AnNpu7ceXvLew05ccD8Zr1OZsdZiB2hLQKK82kTTMDwF7oRKtP3QEJ4RzkeHrmB8Sq0vSV6ZNmszpBCZ0I8p9gAAAABceyJvcmlnaW4iOiJodHRwczovL2ltbWVyc2l2ZS13ZWIuZ2l0aHViLmlvOjQ0MyIsImZlYXR1cmUiOiJXZWJYUkRldmljZSIsImV4cGlyeSI6MTUzNTQxNDQwMH0=">
<title>Fallback Rendering</title>
<link href='css/common.css' rel='stylesheet'></link>
<!--The polyfill is not needed for browser that have native API support,
but is linked by these samples for wider compatibility.-->
<!--script src='https://cdn.jsdelivr.net/npm/webxr-polyfill@latest/build/webxr-polyfill.js'></script-->
<script src='js/webxr-polyfill.js'></script>
<!--This script patches up around implementation differences in past browser versions
so that the samples can always be written against the most recent spec changes.
It won't be necessary after the API has been officially shipped for a bit.-->
<script src='js/webxr-version-shim.js'></script>
<script src='js/cottontail/build/cottontail.js'></script>
<script src='js/webxr-button.js'></script>
</head>
<body>
<header>
<details open>
<summary>Fallback Rendering</summary>
<p>
This sample demonstrates a way to fallback to rendering the scene when
WebXR isn't available.
<a class="back" href="./">Back</a>
</p>
</details>
</header>
<script>
(function () {
'use strict';
// If requested, initialize the WebXR polyfill
if (QueryArgs.getBool('allowPolyfill', false)) {
var polyfill = new WebXRPolyfill();
}
// Apply the version shim after the polyfill is instantiated, to ensure
// that the polyfill also gets patched if necessary.
var versionShim = new WebXRVersionShim();
// XR globals.
let xrButton = null;
let xrImmersiveFrameOfRef = null;
let xrNonImmersiveFrameOfRef = null;
// WebGL scene globals.
let gl = null;
let renderer = null;
let scene = new Scene();
scene.addNode(new Gltf2Node({url: 'media/gltf/space/space.gltf'}));
scene.addNode(new SkyboxNode({url: 'media/textures/milky-way-4k.png'}));
let projectionMatrix = mat4.create();
let viewMatrix = mat4.create();
function initXR() {
xrButton = new XRDeviceButton({
onRequestSession: onRequestSession,
onEndSession: onEndSession
});
document.querySelector('header').appendChild(xrButton.domElement);
if (navigator.xr) {
navigator.xr.requestDevice().then((device) => {
device.supportsSession({immersive: true}).then(() => {
xrButton.setDevice(device);
});
let outputCanvas = document.createElement('canvas');
let ctx = outputCanvas.getContext('xrpresent');
device.requestSession({ outputContext: ctx })
.then((session) => {
document.body.appendChild(outputCanvas);
onSessionStarted(session);
});
}).catch(() => {
// If navigator.xr is found but it doesn't have any devices, we'll
// need to use the fallback rendering path.
initFallback();
});
} else {
// If navigator.xr isn't present in the browser then we need to use
// the fallback rendering path.
initFallback();
}
}
// When we hit the fallback path, we'll need to initialize a few extra
// variables in order to render correctly.
function initFallback() {
initGL();
document.body.appendChild(gl.canvas);
// Using a simple identity matrix for the view.
mat4.identity(viewMatrix);
// We need to track the canvas size in order to resize the WebGL
// backbuffer width and height, as well as update the projection matrix
// and adjust the viewport.
function onResize() {
gl.canvas.width = gl.canvas.offsetWidth * window.devicePixelRatio;
gl.canvas.height = gl.canvas.offsetHeight * window.devicePixelRatio;
mat4.perspective(projectionMatrix, Math.PI*0.4,
gl.canvas.width/gl.canvas.height,
0.1, 1000.0);
gl.viewport(0, 0, gl.drawingBufferWidth, gl.drawingBufferHeight);
}
window.addEventListener('resize', onResize);
onResize();
// We'll kick off the render loop using the window's
// requestAnimationFrame function.
window.requestAnimationFrame(onWindowFrame);
}
// Since both the XR and fallback paths need to do the same WebGL
// initialization code, we've moved that code out to it's own function.
function initGL(compatibleDevice) {
if (gl)
return;
gl = createWebGLContext({
compatibleXRDevice: compatibleDevice
});
renderer = new Renderer(gl);
scene.setRenderer(renderer);
}
function onRequestSession(device) {
let mirrorCanvas = document.createElement('canvas');
let ctx = mirrorCanvas.getContext('xrpresent');
mirrorCanvas.setAttribute('id', 'mirror-canvas');
document.body.appendChild(mirrorCanvas);
device.requestSession({ immersive: true, outputContext: ctx }).then((session) => {
xrButton.setSession(session);
onSessionStarted(session);
});
}
function onSessionStarted(session) {
session.addEventListener('end', onSessionEnded);
initGL(session.device);
session.baseLayer = new XRWebGLLayer(session, gl);
session.requestFrameOfReference('eye-level').then((frameOfRef) => {
if (session.immersive) {
xrImmersiveFrameOfRef = frameOfRef;
} else {
xrNonImmersiveFrameOfRef = frameOfRef;
}
session.requestAnimationFrame(onXRFrame);
});
}
function onEndSession(session) {
session.end();
}
function onSessionEnded(event) {
if (event.session.immersive) {
document.body.removeChild(document.querySelector('#mirror-canvas'));
xrButton.setSession(null);
}
}
function onXRFrame(t, frame) {
let session = frame.session;
let frameOfRef = session.immersive ?
xrImmersiveFrameOfRef :
xrNonImmersiveFrameOfRef;
let pose = frame.getDevicePose(frameOfRef);
session.requestAnimationFrame(onXRFrame);
scene.startFrame();
if (pose) {
gl.bindFramebuffer(gl.FRAMEBUFFER, session.baseLayer.framebuffer);
gl.clear(gl.COLOR_BUFFER_BIT | gl.DEPTH_BUFFER_BIT);
for (let view of frame.views) {
let viewport = session.baseLayer.getViewport(view);
gl.viewport(viewport.x, viewport.y,
viewport.width, viewport.height);
scene.draw(view.projectionMatrix, pose.getViewMatrix(view));
}
}
scene.endFrame();
}
// This is the bulk of the fallback rendering loop. Notice that it looks
// a lot like a simplified version of the XR frame loop. Samples after
// this one will do some work to hide this for code readability purposes.
function onWindowFrame(t) {
window.requestAnimationFrame(onWindowFrame);
scene.startFrame();
// We can skip setting the framebuffer and viewport every frame, because
// it won't change from frame to frame and we're updating the viewport
// only when we resize for efficency.
gl.clear(gl.COLOR_BUFFER_BIT | gl.DEPTH_BUFFER_BIT);
// We're drawing with our own projection and view matrix now, and we
// don't have a list of view to loop through, but otherwise all of the
// WebGL drawing logic is exactly the same.
scene.draw(projectionMatrix, viewMatrix);
scene.endFrame();
}
// Start the XR application.
initXR();
})();
</script>
</body>
</html>