Remove Environment blend mode from spec and explainer (#804)

NellWaliczek · web-flow · commit 40899c5dc742 · 2019-08-15T10:12:29.000-07:00
Removes Environment blend mode from the WebXR spec and explainer.  An associated "add" commit has been made in the webxr-ar-module repository
diff --git a/explainer.md b/explainer.md
@@ -492,29 +492,6 @@ let webglLayer = new XRWebGLLayer(xrSession, gl, { ignoreDepthValues: true });
 
 If `ignoreDepthValues` is not set to `true` the The UA is allowed (but not required) to use depth buffer as it sees fit. As a result, barring compositor access to the depth buffer in this way may lead to certain platform or UA features being unavailable or less robust. To detect if the depth buffer is being used by the compositor, check the `ignoreDepthValues` attribute of the `XRWebGLLayer` after the layer is created. A value of `true` indicates that the depth buffer will not be utilized by the compositor even if `ignoreDepthValues` was set to `false` during layer creation.
 
-### Handling non-opaque displays
-
-Some devices which support the WebXR Device API may use displays that are not fully opaque, or otherwise show your surrounding environment in some capacity. To determine how the display will blend rendered content with the real world, check the `XRSession`'s `environmentBlendMode` attribute. It may currently be one of three values, and more may be added in the future if new display technology necessitates it:
-
-  - `opaque`: The environment is not visible at all through this display. Transparent pixels in the `baseLayer` will appear black. This is the expected mode for most VR headsets. Alpha values will be ignored, with the compositor treating all alpha values as 1.0.
-  - `additive`: The environment is visible through the display and pixels in the `baseLayer` will be shown additively against it. Black pixels will appear fully transparent, and there is typically no way to make a pixel fully opaque. Alpha values will be ignored, with the compositor treating all alpha values as 1.0. This is the expected mode for devices like HoloLens or Magic Leap.
-  - `alpha-blend`: The environment is visible through the display and pixels in the `baseLayer` will be blended with it according to the alpha value of the pixel. Pixels with an alpha value of 1.0 will be fully opaque and pixels with an alpha value of 0.0 will be fully transparent. This is the expected mode for devices which use passthrough video to show the environment such as ARCore or ARKit enabled phones, as well as headsets that utilize passthrough video for AR like the Vive Pro.
-
-When rendering content it's important to know how the content will appear on the display, as that may affect the techniques you use to render. For example, on an `additive` display is used that can only render additive light. This means that the color black appears as fully transparent and expensive graphical effects like shadows may not show up at all. Similarly, if the developer knows that the environment will be visible they may choose to not render an opaque background.
-
-```js
-function drawScene() {
-  renderer.enableShadows(xrSession.environmentBlendMode != 'additive');
-
-  // Only draw a background for the scene if the environment is not visible.
-  if (xrSession.environmentBlendMode == 'opaque') {
-    renderer.drawSkybox();
-  }
-
-  // Draw the reset of the scene.
-}
-```
-
 ### Changing the Field of View for inline sessions
 
 Whenever possible the matrices given by `XRView`'s `projectionMatrix` attribute should make use of physical properties, such as the headset optics or camera lens, to determine the field of view to use. Most inline content, however, won't have any physically based values from which to infer a field of view. In order to provide a unified render pipeline for inline content an arbitrary field of view must be selected.
@@ -597,7 +574,6 @@ enum XRSessionMode {
 }
 
 [SecureContext, Exposed=Window] interface XRSession : EventTarget {
-  readonly attribute XREnvironmentBlendMode environmentBlendMode;
   readonly attribute XRRenderState renderState;
 
   attribute EventHandler onblur;
@@ -616,12 +592,6 @@ enum XRSessionMode {
 // with the window's FrameRequestCallback.
 callback XRFrameRequestCallback = void (DOMHighResTimeStamp time, XRFrame frame);
 
-enum XREnvironmentBlendMode {
-  "opaque",
-  "additive",
-  "alpha-blend",
-};
-
 dictionary XRRenderStateInit {
   double depthNear;
   double depthFar;
diff --git a/index.bs b/index.bs
@@ -372,7 +372,7 @@ enum XRSessionMode {
 </pre>
 
   - A session mode of <dfn enum-value for="XRSessionMode">inline</dfn> indicates that the session's output will be shown as an element in the HTML document. {{inline}} session content MAY be displayed in mono or stereo and MAY allow for [=viewer=] tracking. User agents MUST allow {{inline}} sessions to be created.
-  - A session mode of <dfn enum-value for="XRSessionMode">immersive-vr</dfn> indicates that the session's output will be given [=exclusive access=] to the [=XR/immersive XR device=] display and that content <b>is not</b> intended to be integrated with the user's environment. The {{environmentBlendMode}} for {{immersive-vr}} sessions is expected to be {{opaque}} when possible, but MAY be {{additive}} if the hardware requires it.
+  - A session mode of <dfn enum-value for="XRSessionMode">immersive-vr</dfn> indicates that the session's output will be given [=exclusive access=] to the [=XR/immersive XR device=] display and that content <b>is not</b> intended to be integrated with the user's environment.
 
 In this document, the term <dfn>inline session</dfn> is synonymous with an {{inline}} session and the term <dfn>immersive session</dfn> is synonymous with an {{immersive-vr}} session.
 
@@ -504,12 +504,6 @@ Any interaction with XR hardware is done via an {{XRSession}} object, which can
 The user agent, when possible, <dfn>SHOULD NOT initialize device tracking</dfn> or rendering capabilities until an {{XRSession}} has been acquired. This is to prevent unwanted side effects of engaging the XR systems when they're not actively being used, such as increased battery usage or related utility applications from appearing when first navigating to a page that only wants to test for the presence of XR hardware in order to advertise XR features. Not all XR platforms offer ways to detect the hardware's presence without initializing tracking, however, so this is only a strong recommendation.
 
 <pre class="idl">
-enum XREnvironmentBlendMode {
-  "opaque",
-  "additive",
-  "alpha-blend",
-};
-
 enum XRVisibilityState {
   "visible",
   "visible-blurred",
@@ -518,7 +512,6 @@ enum XRVisibilityState {
 
 [SecureContext, Exposed=Window] interface XRSession : EventTarget {
   // Attributes
-  readonly attribute XREnvironmentBlendMode environmentBlendMode;
   readonly attribute XRVisibilityState visibilityState;
   [SameObject] readonly attribute XRRenderState renderState;
   [SameObject] readonly attribute XRInputSourceArray inputSources;
@@ -711,18 +704,6 @@ When the {{XRInputSource/handedness}}, {{XRInputSource/targetRayMode}}, {{XRInpu
 
 </div>
 
-Each {{XRSession}} has an <dfn for="XRSession">environment blending mode</dfn> value, which is an enum which MUST be set to whichever of the following values best matches the behavior of imagery rendered by the session in relation to the user's surrounding environment.
-
-  - A blend mode of <dfn enum-value for="XREnvironmentBlendMode">opaque</dfn> indicates that the user's surrounding environment is not visible at all. Alpha values in the {{XRRenderState/baseLayer}} will be ignored, with the compositor treating all alpha values as 1.0.
-
-  - A blend mode of <dfn enum-value for="XREnvironmentBlendMode">additive</dfn> indicates that the user's surrounding environment is visible and the {{XRRenderState/baseLayer}} will be shown additively against it. Alpha values in the {{XRRenderState/baseLayer}} will be ignored, with the compositor treating all alpha values as 1.0. When this blend mode is in use black pixels will appear fully transparent, and there is no way to make a pixel appear fully opaque.
-
-  - A blend mode of <dfn enum-value for="XREnvironmentBlendMode">alpha-blend</dfn> indicates that the user's surrounding environment is visible and the {{XRRenderState/baseLayer}} will be blended with it according to the alpha values of each pixel. Pixels with an alpha value of 1.0 will be fully opaque and pixels with an alpha value of 0.0 will be fully transparent.
-
-The <dfn attribute for="XRSession">environmentBlendMode</dfn> attribute returns the {{XRSession}}'s [=environment blending mode=].
-
-Note: Most Virtual Reality devices exhibit {{XREnvironmentBlendMode/"opaque"}} blending behavior. Augmented Reality devices that use transparent optical elements frequently exhibit {{XREnvironmentBlendMode/"additive"}} blending behavior, and Augmented Reality devices that use passthrough cameras frequently exhibit {{XREnvironmentBlendMode/"alpha-blend"}} blending behavior.
-
 Each {{XRSession}} has a <dfn for="XRSession">visibility state</dfn> value, which is an enum which MUST be set to whichever of the following values best matches the state of session.
 
   - A state of <dfn enum-value for="XRVisibilityState">visible</dfn> indicates that imagery rendered by the {{XRSession}} can be seen by the user and {{XRSession/requestAnimationFrame()}} callbacks are processed at the [=XRSession/XR device=]'s native refresh rate. Input is processed by the {{XRSession}} normally.
