Add XREnvironmentBlendMode, configurable by PolyfilledXRDevice. Fixes #…

…16

src/api/XRSession.js

@@ -199,6 +199,13 @@ export default class XRSession extends EventTarget {
    */
   set depthFar(value) { this[PRIVATE].polyfill.depthFar = value; }
 
+  /**
+   * @return {XREnvironmentBlendMode}
+   */
+  get environmentBlendMode() {
+    return this[PRIVATE].polyfill.environmentBlendMode || 'opaque';
+  }
+
   /**
    * @return {XRLayer}
    */

src/devices/PolyfilledXRDevice.js

@@ -28,6 +28,11 @@ export default class PolyfilledXRDevice extends EventTarget {
     this.onWindowResize = this.onWindowResize.bind(this);
 
     this.global.window.addEventListener('resize', this.onWindowResize);
+
+    // Value is used for `XRSession.prototype.environmentBlendMode`
+    // and should be one of XREnvironmentBlendMode types: 'opaque', 'additive',
+    // or 'alpha-blend'.
+    this.environmentBlendMode = 'opaque';
   }
 
   /**

test/api/test-xr-session.js

@@ -45,6 +45,20 @@ describe('API - XRSession', () => {
     assert.equal(session.immersive, false);
   });
 
+  it('has `environmentBlendMode` property from polyfill', async function () {
+    const global = new MockGlobalVR();
+    const polyfill = new WebVRDevice(global, new MockVRDisplay(global));
+    const device = new XRDevice(polyfill);
+    const session = await device.requestSession({ immersive: true });
+
+    polyfill.environmentBlendMode = null;
+    // 'opaque' is default
+    assert.equal(session.environmentBlendMode, 'opaque');
+
+    polyfill.environmentBlendMode = 'alpha-blend';
+    assert.equal(session.environmentBlendMode, 'alpha-blend');
+  });
+
   it('has `outputContext` property set to session options', async function () {
     let options = { immersive: true, outputContext: new XRPresentationContext() };
     let device = createXRDevice();