Fix blits from multisampled renderbuffers to alpha:false WebGL back buffer.

third_party/WebKit/Source/platform/graphics/gpu/DrawingBuffer.cpp

 /*
  * Copyright (c) 2010, Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 571 matching lines @@
   if (!recycled_color_buffer_queue_.IsEmpty()) {
     RefPtr<ColorBuffer> recycled = recycled_color_buffer_queue_.TakeLast();
     if (recycled->receive_sync_token.HasData())
       gl_->WaitSyncTokenCHROMIUM(recycled->receive_sync_token.GetData());
     DCHECK(recycled->size == size_);
     return recycled;
   }
   return CreateColorBuffer(size_);
 }
 
+DrawingBuffer::ScopedRGBEmulationForBlitFramebuffer::
+    ScopedRGBEmulationForBlitFramebuffer(DrawingBuffer* drawing_buffer)
+    : drawing_buffer_(drawing_buffer) {
+  doing_work_ = drawing_buffer->SetupRGBEmulationForBlitFramebuffer();
+}
+
+DrawingBuffer::ScopedRGBEmulationForBlitFramebuffer::
+    ~ScopedRGBEmulationForBlitFramebuffer() {
+  if (doing_work_) {
+    drawing_buffer_->CleanupRGBEmulationForBlitFramebuffer();
+  }
+}
+
 DrawingBuffer::ColorBuffer::ColorBuffer(
     DrawingBuffer* drawing_buffer,
     const ColorBufferParameters& parameters,
     const IntSize& size,
     GLuint texture_id,
     GLuint image_id,
     std::unique_ptr<gfx::GpuMemoryBuffer> gpu_memory_buffer)
     : drawing_buffer(drawing_buffer),
       parameters(parameters),
       size(size),
       texture_id(texture_id),
       image_id(image_id),
       gpu_memory_buffer(std::move(gpu_memory_buffer)) {
   drawing_buffer->ContextGL()->GenMailboxCHROMIUM(mailbox.name);
 }
 
 DrawingBuffer::ColorBuffer::~ColorBuffer() {
   gpu::gles2::GLES2Interface* gl = drawing_buffer->gl_;
   if (receive_sync_token.HasData())
     gl->WaitSyncTokenCHROMIUM(receive_sync_token.GetConstData());
   if (image_id) {
     gl->BindTexture(parameters.target, texture_id);
     gl->ReleaseTexImage2DCHROMIUM(parameters.target, image_id);
+    if (rgb_workaround_texture_id) {
+      gl->BindTexture(parameters.target, rgb_workaround_texture_id);
+      gl->ReleaseTexImage2DCHROMIUM(parameters.target, image_id);
+    }
     gl->DestroyImageCHROMIUM(image_id);
     switch (parameters.target) {
       case GL_TEXTURE_2D:
         // Restore the texture binding for GL_TEXTURE_2D, since the client will
         // expect the previous state.
         if (drawing_buffer->client_)
           drawing_buffer->client_->DrawingBufferClientRestoreTexture2DBinding();
         break;
       case GC3D_TEXTURE_RECTANGLE_ARB:
         // Rectangle textures aren't exposed to WebGL, so don't bother
         // restoring this state (there is no meaningful way to restore it).
         break;
       default:
         NOTREACHED();
         break;
     }
     gpu_memory_buffer.reset();
   }
   gl->DeleteTextures(1, &texture_id);
+  gl->DeleteTextures(1, &rgb_workaround_texture_id);
 }
 
 bool DrawingBuffer::Initialize(const IntSize& size, bool use_multisampling) {
   ScopedStateRestorer scoped_state_restorer(this);
 
   if (gl_->GetGraphicsResetStatusKHR() != GL_NO_ERROR) {
     // Need to try to restore the context again later.
     return false;
   }
 
@@ skipping 620 matching lines @@
   if (ShouldUseChromiumImage() &&
       ContextProvider()->GetCapabilities().chromium_image_rgb_emulation)
     return GL_RGBA8_OES;
   if (ContextProvider()
           ->GetCapabilities()
           .disable_webgl_rgb_multisampling_usage)
     return GL_RGBA8_OES;
   return GL_RGB8_OES;
 }
 
+bool DrawingBuffer::SetupRGBEmulationForBlitFramebuffer() {
+  // We only need to do this work if:
+  //  - The user has selected alpha:false and antialias:false
+  //  - We are using CHROMIUM_image with RGB emulation
+  // macOS is the only platform on which this is necessary.
+
+  if (want_alpha_channel_ || anti_aliasing_mode_ != kNone)
+    return false;
+
+  if (!(ShouldUseChromiumImage() &&
+        ContextProvider()->GetCapabilities().chromium_image_rgb_emulation))
+    return false;
+
+  if (!back_color_buffer_)
+    return false;
+
+  // If for some reason the back buffer doesn't have a CHROMIUM_image,
+  // don't proceed with this workaround.
+  if (!back_color_buffer_->image_id)
+    return false;
+
+  // Before allowing the BlitFramebuffer call to go through, it's necessary
+  // to swap out the RGBA texture that's bound to the CHROMIUM_image
+  // instance with an RGB texture. BlitFramebuffer requires the internal
+  // formats of the source and destination to match when doing a
+  // multisample resolve, and the best way to achieve this without adding
+  // more full-screen blits is to hook up a true RGB texture to the
+  // underlying IOSurface. Unfortunately, on macOS, this rendering path
+  // destroys the alpha channel and requires a fixup afterward, which is
+  // why it isn't used all the time.
+
+  GLuint rgb_texture = back_color_buffer_->rgb_workaround_texture_id;
+  GLenum target = GC3D_TEXTURE_RECTANGLE_ARB;
+  if (!rgb_texture) {
+    gl_->GenTextures(1, &rgb_texture);
+    gl_->BindTexture(target, rgb_texture);
+    gl_->TexParameteri(target, GL_TEXTURE_MAG_FILTER, GL_LINEAR);
+    gl_->TexParameteri(target, GL_TEXTURE_MIN_FILTER, GL_LINEAR);
+    gl_->TexParameteri(target, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
+    gl_->TexParameteri(target, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);
+
+    // Bind this texture to the CHROMIUM_image instance that the color
+    // buffer owns. This is an expensive operation, so it's important that
+    // the result be cached.
+    gl_->BindTexImage2DWithInternalformatCHROMIUM(target, GL_RGB,
+                                                  back_color_buffer_->image_id);
+    back_color_buffer_->rgb_workaround_texture_id = rgb_texture;
+  }
+
+  gl_->FramebufferTexture2D(GL_DRAW_FRAMEBUFFER_ANGLE, GL_COLOR_ATTACHMENT0,
+                            target, rgb_texture, 0);
+  return true;
+}
+
+void DrawingBuffer::CleanupRGBEmulationForBlitFramebuffer() {
+  // This will only be called if SetupRGBEmulationForBlitFramebuffer was.
+  // Put the framebuffer back the way it was, and clear the alpha channel.
+  DCHECK(back_color_buffer_);
+  DCHECK(back_color_buffer_->image_id);
+  GLenum target = GC3D_TEXTURE_RECTANGLE_ARB;
+  gl_->FramebufferTexture2D(GL_DRAW_FRAMEBUFFER_ANGLE, GL_COLOR_ATTACHMENT0,
+                            target, back_color_buffer_->texture_id, 0);

[Zhenyao Mo, 2017/04/19 23:07:34]

Please make sure this was bound before SetupRGBEmulationForBlitFramebuffer

[Ken Russell (switch to Gerrit), 2017/04/20 01:49:18]

Confirmed that it is, in AttachColorBufferToReadFramebuffer, called by
ResizeDefaultFramebuffer and FinishPrepareTextureMailboxGpu.

+  // Clear the alpha channel.
+  gl_->ColorMask(GL_FALSE, GL_FALSE, GL_FALSE, GL_TRUE);
+  gl_->Disable(GL_SCISSOR_TEST);
+  gl_->ClearColor(0, 0, 0, 1);
+  gl_->Clear(GL_COLOR_BUFFER_BIT);
+  DCHECK(client_);
+  client_->DrawingBufferClientRestoreScissorTest();
+  client_->DrawingBufferClientRestoreMaskAndClearValues();
+}
+
 DrawingBuffer::ScopedStateRestorer::ScopedStateRestorer(
     DrawingBuffer* drawing_buffer)
     : drawing_buffer_(drawing_buffer) {
   // If this is a nested restorer, save the previous restorer.
   previous_state_restorer_ = drawing_buffer->state_restorer_;
   drawing_buffer_->state_restorer_ = this;
 }
 
 DrawingBuffer::ScopedStateRestorer::~ScopedStateRestorer() {
   DCHECK_EQ(drawing_buffer_->state_restorer_, this);
@@ skipping 17 matching lines @@
   if (pixel_unpack_buffer_binding_dirty_)
     client->DrawingBufferClientRestorePixelUnpackBufferBinding();
 }
 
 bool DrawingBuffer::ShouldUseChromiumImage() {
   return RuntimeEnabledFeatures::webGLImageChromiumEnabled() &&
          chromium_image_usage_ == kAllowChromiumImage;
 }
 
 }  // namespace blink