[Command buffer] During blit FB, It is invalid if src source and dst source have identical image

gpu/command_buffer/service/gles2_cmd_decoder.cc

Index: gpu/command_buffer/service/gles2_cmd_decoder.cc
diff --git a/gpu/command_buffer/service/gles2_cmd_decoder.cc b/gpu/command_buffer/service/gles2_cmd_decoder.cc
index 7a0243a18d839a4f260dec14eee529a14ddd6c34..57709adf8ec8213158ac9ce747470c7507f8cc7b 100644
--- a/gpu/command_buffer/service/gles2_cmd_decoder.cc
+++ b/gpu/command_buffer/service/gles2_cmd_decoder.cc
@@ -1349,6 +1349,11 @@ class GLES2DecoderImpl : public GLES2Decoder, public ErrorStateClient {
       GLint level,
       GLint layer);
 
+  // Check that whether the currently bound draw framebuffer has image

[Zhenyao Mo, 2016/09/09 16:29:57]

nit: remove that

[yunchao, 2016/09/09 16:47:33]

Done.

+  // that is identical to the read framebuffer's image for blitFramebuffer,
+  // and only check the designated image type by parameter mask.
+  bool FormsFramebufferBlitingFeedbackLoop(GLbitfield mask);
+
   // Check if a framebuffer meets our requirements.
   // Generates |gl_error| if the framebuffer is incomplete.
   bool CheckFramebufferValid(
@@ -4332,6 +4337,60 @@ bool GLES2DecoderImpl::FormsTextureCopyingFeedbackLoop(
   return attachment->FormsFeedbackLoop(texture, level, layer);
 }
 
+bool GLES2DecoderImpl::FormsFramebufferBlitingFeedbackLoop(GLbitfield mask) {
+  Framebuffer* read_framebuffer =
+      framebuffer_state_.bound_read_framebuffer.get();
+  Framebuffer* draw_framebuffer =
+      framebuffer_state_.bound_draw_framebuffer.get();
+  // If both read framebuffer and draw framebuffer are default framebuffer,
+  // They always have the same image.
+  if (!read_framebuffer && !draw_framebuffer)
+    return true;
+  if (!read_framebuffer || !draw_framebuffer)
+    return false;
+  if ((mask & GL_COLOR_BUFFER_BIT) != 0) {
+    const Framebuffer::Attachment* read_buffer =
+        read_framebuffer->GetReadBufferAttachment();
+
+    for (uint32_t ii = 0; ii < group_->max_draw_buffers(); ++ii) {

[Zhenyao Mo, 2016/09/09 16:29:57]

If you go through attachments of the draw_framebuffer, most time it's probably
only one or two attachments, much less iterations.

[yunchao, 2016/09/09 16:47:33]

That's true. But we still need to iterate to cover unusual cases... 

[Zhenyao Mo, 2016/09/09 17:39:32]

We should always optimize against most common use cases. BlitFramebuffer is on
critical path: if webgl is created with antialias = true, then each frame we
need to blit to a non-multisampled texture for compositing. So optimizing it is
important.

+      GLenum drawbuffer = static_cast<GLenum>(GL_DRAW_BUFFER0 + ii);
+      if (draw_framebuffer->GetDrawBuffer(drawbuffer) == GL_NONE) {
+        continue;
+      }
+      GLenum attachment = static_cast<GLenum>(GL_COLOR_ATTACHMENT0 + ii);
+      const Framebuffer::Attachment* draw_buffer =
+          draw_framebuffer->GetAttachment(attachment);
+      if (!draw_buffer) {
+        continue;
+      }
+      if (draw_buffer->IsSameAttachment(read_buffer)) {
+        return true;
+      }
+    }
+  }
+  if ((mask & GL_DEPTH_BUFFER_BIT) != 0) {
+    const Framebuffer::Attachment* depth_buffer_read =
+        read_framebuffer->GetAttachment(GL_DEPTH_ATTACHMENT);
+    const Framebuffer::Attachment* depth_buffer_draw =
+        draw_framebuffer->GetAttachment(GL_DEPTH_ATTACHMENT);
+      if (depth_buffer_draw &&

[Zhenyao Mo, 2016/09/09 16:29:57]

nit: wrong indent

[yunchao, 2016/09/09 16:47:33]

Done.

+          depth_buffer_draw->IsSameAttachment(depth_buffer_read)) {
+      return true;
+    }
+  }
+  if ((mask & GL_STENCIL_BUFFER_BIT) != 0) {
+    const Framebuffer::Attachment* stencil_buffer_read =
+        read_framebuffer->GetAttachment(GL_STENCIL_ATTACHMENT);
+    const Framebuffer::Attachment* stencil_buffer_draw =
+        draw_framebuffer->GetAttachment(GL_STENCIL_ATTACHMENT);
+    if (stencil_buffer_draw &&
+        stencil_buffer_draw->IsSameAttachment(stencil_buffer_read)) {
+      return true;
+    }
+  }
+  return false;
+}
+
 gfx::Size GLES2DecoderImpl::GetBoundReadFramebufferSize() {
   Framebuffer* framebuffer =
       GetFramebufferInfoForTarget(GL_READ_FRAMEBUFFER_EXT);
@@ -7599,6 +7658,12 @@ void GLES2DecoderImpl::DoBlitFramebufferCHROMIUM(
     return;
   }
 
+  if (FormsFramebufferBlitingFeedbackLoop(mask)) {
+    LOCAL_SET_GL_ERROR(GL_INVALID_OPERATION, func_name,
+        "source buffer and destination buffers are identical");
+    return;
+  }
+
   GLenum src_format = GetBoundReadFramebufferInternalFormat();
   GLenum src_type = GetBoundReadFramebufferTextureType();