Bug 1543616 - Call TextureHost::PrepareForUse() when mCompositableCount becomes from 0 to 1 r=nical

By Bug 1529870, the PrepareForUse() is called in WebRenderImageHost::SetCurrentTextureHost(). It works with single buffer mode android SurfaceTexture for WebGL. But it does not work well with video's SurfaceTexture, since multiple TextureHosts are received and a TextureHost might be skipped. The timing of mCompositableCount becomes from 0 to 1 could be used for calling PrepareForUse().

Differential Revision: https://phabricator.services.mozilla.com/D27044

--HG--
extra : moz-landing-system : lando

gfx/layers/composite/TextureHost.h

@@ -597,7 +597,12 @@ class TextureHost : public AtomicRefCountedWithFinalize<TextureHost> {
    */
   virtual bool HasIntermediateBuffer() const { return false; }
 
-  void AddCompositableRef() { ++mCompositableCount; }
+  void AddCompositableRef() {
+    ++mCompositableCount;
+    if (mCompositableCount == 1) {
+      PrepareForUse();
+    }
+  }
 
   void ReleaseCompositableRef() {
     --mCompositableCount;
@@ -681,6 +686,11 @@ class TextureHost : public AtomicRefCountedWithFinalize<TextureHost> {
 
   virtual void UpdatedInternal(const nsIntRegion* Region) {}
 
+  /**
+   * Called when mCompositableCount becomes from 0 to 1.
+   */
+  virtual void PrepareForUse() {}
+
   /**
    * Called when mCompositableCount becomes 0.
    */

gfx/layers/wr/WebRenderImageHost.cpp

@@ -163,14 +163,6 @@ void WebRenderImageHost::SetCurrentTextureHost(TextureHost* aTexture) {
   if (aTexture == mCurrentTextureHost.get()) {
     return;
   }
-
-  if (aTexture && aTexture->AsWebRenderTextureHost()) {
-    // If WebRenderTextureHost wraps SurfaceTextureHost, it is important to call
-    // PrepareForUse for each texture that we receive.
-    // See RenderAndroidSurfaceTextureHostOGL::PrepareForUse.
-    aTexture->AsWebRenderTextureHost()->PrepareForUse();
-  }
-
   mCurrentTextureHost = aTexture;
 }
 

gfx/layers/wr/WebRenderTextureHost.h

@@ -60,7 +60,7 @@ class WebRenderTextureHost : public TextureHost {
 
   WebRenderTextureHost* AsWebRenderTextureHost() override { return this; }
 
-  virtual void PrepareForUse();
+  virtual void PrepareForUse() override;
 
   wr::ExternalImageId GetExternalImageKey() { return mExternalImageId; }