Clean up multisampled color mask workaround for DrawingBuffer.

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 188 matching lines @@
 {
     if (m_filterQuality != filterQuality) {
         m_filterQuality = filterQuality;
         if (m_layer)
             m_layer->setNearestNeighbor(filterQuality == kNone_SkFilterQuality);
     }
 }
 
 bool DrawingBuffer::requiresAlphaChannelToBePreserved()
 {
-    // When an explicit resolve is required, clients draw into a render buffer
-    // which is never backed by an IOSurface.
-    if (m_antiAliasingMode == MSAAExplicitResolve)
-        return false;
-    return !m_drawFramebufferBinding && !m_wantAlphaChannel && m_colorBuffer.imageId && contextProvider()->getCapabilities().chromium_image_rgb_emulation;
+    return !m_drawFramebufferBinding && defaultBufferRequiresAlphaChannelToBePreserved();
+}
+
+bool DrawingBuffer::defaultBufferRequiresAlphaChannelToBePreserved()
+{
+    if (wantExplicitResolve()) {
+        return !m_wantAlphaChannel && getMultisampledRenderbufferFormat() == GL_RGBA8_OES;
+    }
+
+    return !m_wantAlphaChannel && m_colorBuffer.imageId && contextProvider()->getCapabilities().chromium_image_rgb_emulation;
 }
 
 void DrawingBuffer::freeRecycledMailboxes()
 {
     if (m_recycledMailboxQueue.isEmpty())
         return;
     while (!m_recycledMailboxQueue.isEmpty())
         deleteMailbox(m_recycledMailboxQueue.takeLast());
 }
 
@@ skipping 99 matching lines @@
 {
 #if OS(MACOSX)
     // A CHROMIUM_image backed texture requires a specialized set of parameters
     // on OSX.
     TextureParameters parameters;
     parameters.target = GC3D_TEXTURE_RECTANGLE_ARB;
 
     if (m_wantAlphaChannel) {
         parameters.creationInternalColorFormat = GL_RGBA;
         parameters.internalColorFormat = GL_RGBA;
-        parameters.internalRenderbufferFormat = GL_RGBA8_OES;
     } else if (contextProvider()->getCapabilities().chromium_image_rgb_emulation) {
         parameters.creationInternalColorFormat = GL_RGB;
         parameters.internalColorFormat = GL_RGBA;
-        parameters.internalRenderbufferFormat = GL_RGB8_OES;
     } else {
         parameters.creationInternalColorFormat = GL_RGB;
         parameters.internalColorFormat = GL_RGB;
-        parameters.internalRenderbufferFormat = GL_RGB8_OES;
     }
 
     // Unused when CHROMIUM_image is being used.
     parameters.colorFormat = 0;
     return parameters;
 #else
     return defaultTextureParameters();
 #endif
 }
 
 DrawingBuffer::TextureParameters DrawingBuffer::defaultTextureParameters()
 {
     TextureParameters parameters;
     parameters.target = GL_TEXTURE_2D;
     if (m_wantAlphaChannel) {
         parameters.internalColorFormat = GL_RGBA;
         parameters.creationInternalColorFormat = GL_RGBA;
         parameters.colorFormat = GL_RGBA;
-        parameters.internalRenderbufferFormat = GL_RGBA8_OES;
     } else {
         parameters.internalColorFormat = GL_RGB;
         parameters.creationInternalColorFormat = GL_RGB;
         parameters.colorFormat = GL_RGB;
-        parameters.internalRenderbufferFormat = GL_RGB8_OES;
     }
     return parameters;
 }
 
 void DrawingBuffer::mailboxReleasedWithoutRecycling(const WebExternalTextureMailbox& mailbox)
 {
     ASSERT(m_textureMailboxes.size());
     // Ensure not to call the destructor until deleteMailbox() is completed.
     RefPtr<DrawingBuffer> self = this;
     deleteMailbox(mailbox);
@@ skipping 205 matching lines @@
 
     if (m_multisampleFBO)
         m_gl->DeleteFramebuffers(1, &m_multisampleFBO);
 
     if (m_fbo)
         m_gl->DeleteFramebuffers(1, &m_fbo);
 
     if (m_multisampleRenderbuffer)
         m_gl->DeleteRenderbuffers(1, &m_multisampleRenderbuffer);
 
-    if (m_intermediateFBO)
-        m_gl->DeleteFramebuffers(1, &m_intermediateFBO);
-
-    if (m_intermediateRenderbuffer)
-        m_gl->DeleteRenderbuffers(1, &m_intermediateRenderbuffer);
-
     if (m_depthStencilBuffer)
         m_gl->DeleteRenderbuffers(1, &m_depthStencilBuffer);
 
     if (m_colorBuffer.textureId) {
         deleteChromiumImageForTexture(&m_colorBuffer);
         m_gl->DeleteTextures(1, &m_colorBuffer.textureId);
     }
 
     setSize(IntSize());
 
@@ skipping 18 matching lines @@
     m_gl->TexParameteri(parameters.target, GL_TEXTURE_WRAP_S, GL_CLAMP_TO_EDGE);
     m_gl->TexParameteri(parameters.target, GL_TEXTURE_WRAP_T, GL_CLAMP_TO_EDGE);
     return offscreenColorTexture;
 }
 
 bool DrawingBuffer::resizeMultisampleFramebuffer(const IntSize& size)
 {
     DCHECK(wantExplicitResolve());
     m_gl->BindFramebuffer(GL_FRAMEBUFFER, m_multisampleFBO);
     m_gl->BindRenderbuffer(GL_RENDERBUFFER, m_multisampleRenderbuffer);
-    m_gl->RenderbufferStorageMultisampleCHROMIUM(GL_RENDERBUFFER, m_sampleCount, m_colorBuffer.parameters.internalRenderbufferFormat, size.width(), size.height());
+    m_gl->RenderbufferStorageMultisampleCHROMIUM(GL_RENDERBUFFER, m_sampleCount, getMultisampledRenderbufferFormat(), size.width(), size.height());
 
     if (m_gl->GetError() == GL_OUT_OF_MEMORY)
         return false;
 
     m_gl->FramebufferRenderbuffer(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_RENDERBUFFER, m_multisampleRenderbuffer);
 
-    if (m_intermediateFBO) {
-        m_gl->BindFramebuffer(GL_FRAMEBUFFER, m_intermediateFBO);
-        m_gl->BindRenderbuffer(GL_RENDERBUFFER, m_intermediateRenderbuffer);
-        m_gl->RenderbufferStorage(GL_RENDERBUFFER, m_colorBuffer.parameters.internalRenderbufferFormat, size.width(), size.height());
-
-        if (m_gl->GetError() == GL_OUT_OF_MEMORY)
-            return false;
-
-        m_gl->FramebufferRenderbuffer(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_RENDERBUFFER, m_intermediateRenderbuffer);
-        if (m_gl->CheckFramebufferStatus(GL_FRAMEBUFFER) != GL_FRAMEBUFFER_COMPLETE)
-            return false;
-
-        m_gl->BindFramebuffer(GL_FRAMEBUFFER, m_multisampleFBO);
-    }
     return true;
 }
 
 void DrawingBuffer::resizeDepthStencil(const IntSize& size)
 {
     m_gl->BindFramebuffer(GL_FRAMEBUFFER, m_multisampleFBO ? m_multisampleFBO : m_fbo);
     if (!m_depthStencilBuffer)
         m_gl->GenRenderbuffers(1, &m_depthStencilBuffer);
     m_gl->BindRenderbuffer(GL_RENDERBUFFER, m_depthStencilBuffer);
     if (m_antiAliasingMode == MSAAImplicitResolve)
@@ skipping 87 matching lines @@
             break;
         } while (!adjustedSize.isEmpty());
 
         setSize(adjustedSize);
 
         if (adjustedSize.isEmpty())
             return false;
     }
 
     m_gl->Disable(GL_SCISSOR_TEST);
-    m_gl->ClearColor(0, 0, 0, 0);
-    m_gl->ColorMask(true, true, true, !requiresAlphaChannelToBePreserved());
+    m_gl->ClearColor(0, 0, 0, defaultBufferRequiresAlphaChannelToBePreserved() ? 1 : 0);
+    m_gl->ColorMask(true, true, true, true);
 
     GLbitfield clearMask = GL_COLOR_BUFFER_BIT;
     if (!!m_depthStencilBuffer) {
         m_gl->ClearDepthf(1.0f);
         clearMask |= GL_DEPTH_BUFFER_BIT;
         m_gl->DepthMask(true);
     }
     if (!!m_depthStencilBuffer) {
         m_gl->ClearStencil(0);
         clearMask |= GL_STENCIL_BUFFER_BIT;
@@ skipping 11 matching lines @@
         m_gl->BindFramebuffer(GL_DRAW_FRAMEBUFFER_ANGLE, m_fbo);
 
         if (m_scissorEnabled)
             m_gl->Disable(GL_SCISSOR_TEST);
 
         int width = m_size.width();
         int height = m_size.height();
         // Use NEAREST, because there is no scale performed during the blit.
         GLuint filter = GL_NEAREST;
 
-        // If the destination has a different color format than the source, then
-        // first resolve to an intermediary renderbuffer with the same color
-        // format.
-        // If this extra blit proves to be a performance problem, it can be
-        // bypassed on most GPUs by performing client side GL_RGBA emulation on
-        // the source renderbuffer.
-        // https://bugs.chromium.org/p/chromium/issues/detail?id=595948#c30
-        if (m_colorBuffer.parameters.internalColorFormat == GL_RGBA && m_colorBuffer.parameters.internalRenderbufferFormat == GL_RGB8_OES) {
-            if (!m_intermediateFBO) {
-                DCHECK(!m_intermediateRenderbuffer);
-                m_gl->GenRenderbuffers(1, &m_intermediateRenderbuffer);
-                m_gl->BindRenderbuffer(GL_RENDERBUFFER, m_intermediateRenderbuffer);
-                m_gl->RenderbufferStorage(GL_RENDERBUFFER, GL_RGB8, width, height);
+        m_gl->BlitFramebufferCHROMIUM(0, 0, width, height, 0, 0, width, height, GL_COLOR_BUFFER_BIT, filter);
 
-                m_gl->GenFramebuffers(1, &m_intermediateFBO);
-                m_gl->BindFramebuffer(GL_DRAW_FRAMEBUFFER_ANGLE, m_intermediateFBO);
-                m_gl->FramebufferRenderbuffer(GL_DRAW_FRAMEBUFFER_ANGLE, GL_COLOR_ATTACHMENT0, GL_RENDERBUFFER, m_intermediateRenderbuffer);
-                m_gl->BindRenderbuffer(GL_RENDERBUFFER, m_renderbufferBinding);
-            }
+        // The multisampled renderbuffer colormask doesn't actually mask the
+        // alpha channel. Clear the alpha channel of |m_fbo|.

[Ken Russell (switch to Gerrit), 2016/05/05 18:19:23]

Please mention in the comment that there were bugs in the handling of
glColorMask with multisampled renderbuffers on some GPUs, in particular older
AMD GPUs on Mac OS X.

[erikchen, 2016/05/05 18:33:27]

Done.

+        if (defaultBufferRequiresAlphaChannelToBePreserved()
+            && contextProvider()->getCapabilities().disable_webgl_multisampling_color_mask_usage) {
+            m_gl->ClearColor(0, 0, 0, 1);
+            m_gl->ColorMask(false, false, false, true);
+            m_gl->Clear(GL_COLOR_BUFFER_BIT);
 
-            m_gl->BindFramebuffer(GL_DRAW_FRAMEBUFFER_ANGLE, m_intermediateFBO);
-            m_gl->BlitFramebufferCHROMIUM(0, 0, width, height, 0, 0, width, height, GL_COLOR_BUFFER_BIT, filter);
-
-            m_gl->BindFramebuffer(GL_READ_FRAMEBUFFER_ANGLE, m_intermediateFBO);
-            m_gl->BindFramebuffer(GL_DRAW_FRAMEBUFFER_ANGLE, m_fbo);
+            m_gl->ClearColor(m_clearColor[0], m_clearColor[1], m_clearColor[2], m_clearColor[3]);
+            m_gl->ColorMask(m_colorMask[0], m_colorMask[1], m_colorMask[2], m_colorMask[3]);
         }
 
-        m_gl->BlitFramebufferCHROMIUM(0, 0, width, height, 0, 0, width, height, GL_COLOR_BUFFER_BIT, filter);
-
         if (m_scissorEnabled)
             m_gl->Enable(GL_SCISSOR_TEST);
     }
 
     m_gl->BindFramebuffer(GL_FRAMEBUFFER, m_fbo);
     if (m_antiAliasingMode == ScreenSpaceAntialiasing) {
         m_gl->ApplyScreenSpaceAntialiasingCHROMIUM();
     }
     m_contentsChangeCommitted = true;
 }
@@ skipping 236 matching lines @@
 bool DrawingBuffer::wantExplicitResolve()
 {
     return m_antiAliasingMode == MSAAExplicitResolve;
 }
 
 bool DrawingBuffer::wantDepthOrStencil()
 {
     return m_wantDepth || m_wantStencil;
 }
 
+GLenum DrawingBuffer::getMultisampledRenderbufferFormat()
+{
+    DCHECK(wantExplicitResolve());
+    if (m_wantAlphaChannel)
+        return GL_RGBA8_OES;
+    if (contextProvider()->getCapabilities().chromium_image_rgb_emulation)
+        return GL_RGBA8_OES;
+    return GL_RGB8_OES;
+}
+
 void DrawingBuffer::restoreTextureBindings()
 {
     // This class potentially modifies the bindings for GL_TEXTURE_2D and
     // GL_TEXTURE_RECTANGLE. Only GL_TEXTURE_2D needs to be restored since
     // the public interface for WebGL does not support GL_TEXTURE_RECTANGLE.
     m_gl->BindTexture(GL_TEXTURE_2D, m_texture2DBinding);
 }
 
 } // namespace blink