Reallocate multisample_renderbuffer when GPU switching

This is a temporary patch that is not well refactored but seems to make the following case work properly:
* Init webgl context with low-power gpu, switch tab to one using high-power, and switch back. It renders correctly now before the os switch back to low-power.

This patch doesn't work with:
* Same tab switching case where user allocated multisampled buffer under a webgl 2 context
* Same tab switching case with preseverDrawingbuffer: true.

We'd better land this patch after the gpu pixel test is landed.

Bug: 681341
Change-Id: I9c834d11ee0456545600819f2322dceb38f8a59a
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1812102Reviewed-by: Zhenyao Mo <zmo@chromium.org>
Reviewed-by: Kenneth Russell <kbr@chromium.org>
Commit-Queue: Shrek Shao <shrekshao@google.com>
Cr-Commit-Position: refs/heads/master@{#703425}

third_party/blink/renderer/platform/graphics/gpu/drawing_buffer.cc

@@ -1063,33 +1063,9 @@ bool DrawingBuffer::ResizeDefaultFramebuffer(const IntSize& size) {
   AttachColorBufferToReadFramebuffer();
 
   if (WantExplicitResolve()) {
-    state_restorer_->SetFramebufferBindingDirty();
-    state_restorer_->SetRenderbufferBindingDirty();
-    gl_->BindFramebuffer(GL_FRAMEBUFFER, multisample_fbo_);
-    gl_->BindRenderbuffer(GL_RENDERBUFFER, multisample_renderbuffer_);
-    // Note that the multisample rendertarget will allocate an alpha channel
-    // based on |have_alpha_channel_|, not |allocate_alpha_channel_|, since it
-    // will resolve into the ColorBuffer.
-    GLenum internal_format = have_alpha_channel_ ? GL_RGBA8_OES : GL_RGB8_OES;
-    if (use_half_float_storage_) {
-      DCHECK(want_alpha_channel_);
-      internal_format = GL_RGBA16F_EXT;
-    }
-    if (has_eqaa_support) {
-      gl_->RenderbufferStorageMultisampleAdvancedAMD(
-          GL_RENDERBUFFER, sample_count_, eqaa_storage_sample_count_,
-          internal_format, size.Width(), size.Height());
-    } else {
-      gl_->RenderbufferStorageMultisampleCHROMIUM(
-          GL_RENDERBUFFER, sample_count_, internal_format, size.Width(),
-          size.Height());
-    }
-
-    if (gl_->GetError() == GL_OUT_OF_MEMORY)
+    if (!ReallocateMultisampleRenderbuffer(size)) {
       return false;
-
-    gl_->FramebufferRenderbuffer(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0,
-                                 GL_RENDERBUFFER, multisample_renderbuffer_);
+    }
   }
 
   if (WantDepthOrStencil()) {
@@ -1271,10 +1247,46 @@ void DrawingBuffer::ResolveIfNeeded() {
 
   auto* gl = ContextProvider()->ContextGL();
   if (gl->DidGpuSwitch() == GL_TRUE) {
-    // TODO(crbug.com/681341): reallocate multi-sampled render buffer.
+    // TODO(crbug.com/681341): handle preserveDrawingBuffer:true, and
+    // user-allocated multisampled renderbuffers, by dispatching a context lost
+    // event.
+    if (WantExplicitResolve()) {
+      ReallocateMultisampleRenderbuffer(size_);
+    }
   }
 }
 
+bool DrawingBuffer::ReallocateMultisampleRenderbuffer(const IntSize& size) {
+  state_restorer_->SetFramebufferBindingDirty();
+  state_restorer_->SetRenderbufferBindingDirty();
+  gl_->BindFramebuffer(GL_FRAMEBUFFER, multisample_fbo_);
+  gl_->BindRenderbuffer(GL_RENDERBUFFER, multisample_renderbuffer_);
+  // Note that the multisample rendertarget will allocate an alpha channel
+  // based on |have_alpha_channel_|, not |allocate_alpha_channel_|, since it
+  // will resolve into the ColorBuffer.
+  GLenum internal_format = have_alpha_channel_ ? GL_RGBA8_OES : GL_RGB8_OES;
+  if (use_half_float_storage_) {
+    DCHECK(want_alpha_channel_);
+    internal_format = GL_RGBA16F_EXT;
+  }
+  if (has_eqaa_support) {
+    gl_->RenderbufferStorageMultisampleAdvancedAMD(
+        GL_RENDERBUFFER, sample_count_, eqaa_storage_sample_count_,
+        internal_format, size.Width(), size.Height());
+  } else {
+    gl_->RenderbufferStorageMultisampleCHROMIUM(GL_RENDERBUFFER, sample_count_,
+                                                internal_format, size.Width(),
+                                                size.Height());
+  }
+
+  if (gl_->GetError() == GL_OUT_OF_MEMORY)
+    return false;
+
+  gl_->FramebufferRenderbuffer(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0,
+                               GL_RENDERBUFFER, multisample_renderbuffer_);
+  return true;
+}
+
 void DrawingBuffer::RestoreFramebufferBindings() {
   client_->DrawingBufferClientRestoreFramebufferBinding();
 }

third_party/blink/renderer/platform/graphics/gpu/drawing_buffer.h

@@ -474,6 +474,10 @@ class PLATFORM_EXPORT DrawingBuffer : public cc::TextureLayerClient,
   bool SetupRGBEmulationForBlitFramebuffer(bool is_user_draw_framebuffer_bound);
   void CleanupRGBEmulationForBlitFramebuffer();
 
+  // Reallocate Multisampled renderbuffer, used by explicit resolve when resize
+  // and GPU switch
+  bool ReallocateMultisampleRenderbuffer(const IntSize&);
+
   // Weak, reset by beginDestruction.
   Client* client_ = nullptr;