Bug 1284324 - Implement Canvas Layer mirrors r=bas

- When a canvas layer is set to mirror, it copies the
  texture from the canvas rather than changing the
  texture factory with Morph().
- This is useful when a canvas content will be sent to
  multiple devices simultaneously, such as a VR HMD
  and a 2d monitor mirror.
- This is used by the WebVR 1.0 API, in Bug 1250244

MozReview-Commit-ID: JfMSockO2uz

dom/canvas/CanvasRenderingContext2D.cpp

@@ -5811,8 +5811,14 @@ CanvasRenderingContext2D::GetBufferProvider(LayerManager* aManager)
 already_AddRefed<Layer>
 CanvasRenderingContext2D::GetCanvasLayer(nsDisplayListBuilder* aBuilder,
                                          Layer *aOldLayer,
-                                         LayerManager *aManager)
+                                         LayerManager *aManager,
+                                         bool aMirror /* = false */)
 {
+  if (aMirror) {
+    // Not supported for CanvasRenderingContext2D
+    return nullptr;
+  }
+
   if (mOpaque || mIsSkiaGL) {
     // If we're opaque then make sure we have a surface so we paint black
     // instead of transparent.

dom/canvas/CanvasRenderingContext2D.h

@@ -466,7 +466,8 @@ public:
   mozilla::layers::PersistentBufferProvider* GetBufferProvider(mozilla::layers::LayerManager* aManager);
   already_AddRefed<Layer> GetCanvasLayer(nsDisplayListBuilder* aBuilder,
                                          Layer* aOldLayer,
-                                         LayerManager* aManager) override;
+                                         LayerManager* aManager,
+                                         bool aMirror = false) override;
   virtual bool ShouldForceInactiveLayer(LayerManager* aManager) override;
   void MarkContextClean() override;
   void MarkContextCleanForFrameCapture() override;

dom/canvas/ImageBitmapRenderingContext.cpp

@@ -214,8 +214,14 @@ ImageBitmapRenderingContext::Reset()
 already_AddRefed<Layer>
 ImageBitmapRenderingContext::GetCanvasLayer(nsDisplayListBuilder* aBuilder,
                                             Layer* aOldLayer,
-                                            LayerManager* aManager)
+                                            LayerManager* aManager,
+                                            bool aMirror /* = false */)
 {
+  if (aMirror) {
+    // Not supported for ImageBitmapRenderingContext
+    return nullptr;
+  }
+
   if (!mImage) {
     // No DidTransactionCallback will be received, so mark the context clean
     // now so future invalidations will be dispatched.

dom/canvas/ImageBitmapRenderingContext.h

@@ -70,7 +70,8 @@ public:
   NS_IMETHOD Reset() override;
   virtual already_AddRefed<Layer> GetCanvasLayer(nsDisplayListBuilder* aBuilder,
                                                  Layer* aOldLayer,
-                                                 LayerManager* aManager) override;
+                                                 LayerManager* aManager,
+                                                 bool aMirror = false) override;
   virtual void MarkContextClean() override;
 
   NS_IMETHOD Redraw(const gfxRect& aDirty) override;

dom/canvas/WebGLContext.cpp

@@ -1265,6 +1265,7 @@ WebGLContext::UpdateLastUseIndex()
 }
 
 static uint8_t gWebGLLayerUserData;
+static uint8_t gWebGLMirrorLayerUserData;
 
 class WebGLContextUserData : public LayerUserData
 {
@@ -1307,13 +1308,14 @@ private:
 already_AddRefed<layers::Layer>
 WebGLContext::GetCanvasLayer(nsDisplayListBuilder* builder,
                              Layer* oldLayer,
-                             LayerManager* manager)
+                             LayerManager* manager,
+                             bool aMirror /*= false*/)
 {
     if (IsContextLost())
         return nullptr;
 
     if (!mResetLayer && oldLayer &&
-        oldLayer->HasUserData(&gWebGLLayerUserData)) {
+        oldLayer->HasUserData(aMirror ? &gWebGLMirrorLayerUserData : &gWebGLLayerUserData)) {
         RefPtr<layers::Layer> ret = oldLayer;
         return ret.forget();
     }
@@ -1325,7 +1327,7 @@ WebGLContext::GetCanvasLayer(nsDisplayListBuilder* builder,
     }
 
     WebGLContextUserData* userData = nullptr;
-    if (builder->IsPaintingToWindow() && mCanvasElement) {
+    if (builder->IsPaintingToWindow() && mCanvasElement && !aMirror) {
         // Make the layer tell us whenever a transaction finishes (including
         // the current transaction), so we can clear our invalidation state and
         // start invalidating again. We need to do this for the layer that is
@@ -1345,13 +1347,14 @@ WebGLContext::GetCanvasLayer(nsDisplayListBuilder* builder,
             WebGLContextUserData::PreTransactionCallback, userData);
     }
 
-    canvasLayer->SetUserData(&gWebGLLayerUserData, userData);
+    canvasLayer->SetUserData(aMirror ? &gWebGLMirrorLayerUserData : &gWebGLLayerUserData, userData);
 
     CanvasLayer::Data data;
     data.mGLContext = gl;
     data.mSize = nsIntSize(mWidth, mHeight);
     data.mHasAlpha = gl->Caps().alpha;
     data.mIsGLAlphaPremult = IsPremultAlpha() || !data.mHasAlpha;
+    data.mIsMirror = aMirror;
 
     canvasLayer->Initialize(data);
     uint32_t flags = gl->Caps().alpha ? 0 : Layer::CONTENT_OPAQUE;

dom/canvas/WebGLContext.h

@@ -333,7 +333,8 @@ public:
 
     already_AddRefed<Layer>
     GetCanvasLayer(nsDisplayListBuilder* builder, Layer* oldLayer,
-                   LayerManager* manager) override;
+                   LayerManager* manager,
+                   bool aMirror = false) override;
 
     // Note that 'clean' here refers to its invalidation state, not the
     // contents of the buffer.

dom/canvas/nsICanvasRenderingContextInternal.h

@@ -135,7 +135,8 @@ public:
   // one for the given layer manager if not available.
   virtual already_AddRefed<Layer> GetCanvasLayer(nsDisplayListBuilder* builder,
                                                  Layer *oldLayer,
-                                                 LayerManager *manager) = 0;
+                                                 LayerManager *manager,
+                                                 bool aMirror = false) = 0;
 
   // Return true if the canvas should be forced to be "inactive" to ensure
   // it can be drawn to the screen even if it's too large to be blitted by

gfx/layers/CopyableCanvasLayer.cpp

@@ -37,6 +37,7 @@ CopyableCanvasLayer::CopyableCanvasLayer(LayerManager* aLayerManager, void *aImp
   , mGLFrontbuffer(nullptr)
   , mIsAlphaPremultiplied(true)
   , mOriginPos(gl::OriginPos::TopLeft)
+  , mIsMirror(false)
 {
   MOZ_COUNT_CTOR(CopyableCanvasLayer);
 }
@@ -55,6 +56,7 @@ CopyableCanvasLayer::Initialize(const Data& aData)
     mGLContext = aData.mGLContext;
     mIsAlphaPremultiplied = aData.mIsGLAlphaPremult;
     mOriginPos = gl::OriginPos::BottomLeft;
+    mIsMirror = aData.mIsMirror;
 
     MOZ_ASSERT(mGLContext->IsOffscreen(), "canvas gl context isn't offscreen");
 

gfx/layers/CopyableCanvasLayer.h

@@ -58,6 +58,7 @@ protected:
 
   bool mIsAlphaPremultiplied;
   gl::OriginPos mOriginPos;
+  bool mIsMirror;
 
   RefPtr<gfx::DataSourceSurface> mCachedTempSurface;
 

gfx/layers/Layers.h

@@ -2375,6 +2375,7 @@ public:
       , mSize(0,0)
       , mHasAlpha(false)
       , mIsGLAlphaPremult(true)
+      , mIsMirror(false)
     { }
 
     // One of these three must be specified for Canvas2D, but never more than one
@@ -2393,6 +2394,10 @@ public:
 
     // Whether mGLContext contains data that is alpha-premultiplied.
     bool mIsGLAlphaPremult;
+
+    // Whether the canvas front buffer is already being rendered somewhere else.
+    // When true, do not swap buffers or Morph() to another factory on mGLContext
+    bool mIsMirror;
   };
 
   /**

gfx/layers/client/CanvasClient.cpp

@@ -411,6 +411,11 @@ CanvasClientSharedSurface::UpdateRenderer(gfx::IntSize aSize, Renderer& aRendere
       gfxCriticalError() << "Invalid canvas front buffer";
       return;
     }
+  } else if (layer && layer->mIsMirror) {
+    mShSurfClient = CloneSurface(gl->Screen()->Front()->Surf(), layer->mFactory.get());
+    if (!mShSurfClient) {
+      return;
+    }
   } else {
     mShSurfClient = gl->Screen()->Front();
     if (mShSurfClient && mShSurfClient->GetAllocator() &&

gfx/layers/client/ClientCanvasLayer.cpp

@@ -67,7 +67,7 @@ ClientCanvasLayer::Initialize(const Data& aData)
 
   UniquePtr<SurfaceFactory> factory = GLScreenBuffer::CreateFactory(mGLContext, caps, forwarder, mFlags);
 
-  if (mGLFrontbuffer) {
+  if (mGLFrontbuffer || aData.mIsMirror) {
     // We're using a source other than the one in the default screen.
     // (SkiaGL)
     mFactory = Move(factory);