WebGL GL_RGB emulation to support IOSurfaces on Mac.

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

Index: third_party/WebKit/Source/platform/graphics/gpu/DrawingBuffer.cpp
diff --git a/third_party/WebKit/Source/platform/graphics/gpu/DrawingBuffer.cpp b/third_party/WebKit/Source/platform/graphics/gpu/DrawingBuffer.cpp
index 82f55a9e8de826c01a1d1b75256d58fe05b013e0..e99b32a278616bb210fc8f28f7a07bd3106f34ee 100644
--- a/third_party/WebKit/Source/platform/graphics/gpu/DrawingBuffer.cpp
+++ b/third_party/WebKit/Source/platform/graphics/gpu/DrawingBuffer.cpp
@@ -31,6 +31,7 @@
 #include "platform/graphics/gpu/DrawingBuffer.h"
 
 #include "gpu/command_buffer/client/gles2_interface.h"
+#include "gpu/command_buffer/common/capabilities.h"
 #include "platform/RuntimeEnabledFeatures.h"
 #include "platform/TraceEvent.h"
 #include "platform/graphics/GraphicsLayer.h"
@@ -135,6 +136,7 @@ DrawingBuffer::DrawingBuffer(
     , m_texture2DBinding(0)
     , m_drawFramebufferBinding(0)
     , m_readFramebufferBinding(0)
+    , m_renderbufferBinding(0)
     , m_activeTextureUnit(GL_TEXTURE0)
     , m_contextProvider(std::move(contextProvider))
     , m_context(m_contextProvider->context3d())
@@ -148,6 +150,8 @@ DrawingBuffer::DrawingBuffer(
     , m_fbo(0)
     , m_depthStencilBuffer(0)
     , m_multisampleFBO(0)
+    , m_multisampleIntermediateFBO(0)
+    , m_multisampleIntermediateRenderbuffer(0)
     , m_multisampleColorBuffer(0)
     , m_contentsChanged(true)
     , m_contentsChangeCommitted(false)
@@ -225,6 +229,15 @@ void DrawingBuffer::setFilterQuality(SkFilterQuality filterQuality)
     }
 }
 
+bool DrawingBuffer::requiresRGBEmulation()
+{
+    // 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;
+}
+
 void DrawingBuffer::freeRecycledMailboxes()
 {
     if (m_recycledMailboxQueue.isEmpty())
@@ -343,9 +356,23 @@ DrawingBuffer::TextureParameters DrawingBuffer::chromiumImageTextureParameters()
     // on OSX.
     TextureParameters parameters;
     parameters.target = GC3D_TEXTURE_RECTANGLE_ARB;
-    parameters.internalColorFormat = GL_RGBA;
-    parameters.internalRenderbufferFormat = GL_RGBA8_OES;
-    parameters.colorFormat = GL_RGBA;
+
+    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.

[Ken Russell (switch to Gerrit), 2016/04/29 09:33:09]

Unused when CHROMIUM_image is being used, right? Does it need to be set if
falling back to use a regular texture?

[erikchen, 2016/05/03 22:58:07]

Correct. I updated the comment. Fallback textures use 
DrawingBuffer::defaultTextureParameters.

+    parameters.colorFormat = 0;
     return parameters;
 #else
     return defaultTextureParameters();
@@ -358,10 +385,12 @@ DrawingBuffer::TextureParameters DrawingBuffer::defaultTextureParameters()
     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;
     }
@@ -586,6 +615,12 @@ void DrawingBuffer::beginDestruction()
     if (m_multisampleColorBuffer)
         m_gl->DeleteRenderbuffers(1, &m_multisampleColorBuffer);
 
+    if (m_multisampleIntermediateFBO)
+        m_gl->DeleteFramebuffers(1, &m_multisampleIntermediateFBO);
+
+    if (m_multisampleIntermediateRenderbuffer)
+        m_gl->DeleteRenderbuffers(1, &m_multisampleIntermediateRenderbuffer);
+
     if (m_depthStencilBuffer)
         m_gl->DeleteRenderbuffers(1, &m_depthStencilBuffer);
 
@@ -749,7 +784,7 @@ bool DrawingBuffer::reset(const IntSize& newSize, bool wantDepthOrStencilBuffer)
 
     m_gl->Disable(GL_SCISSOR_TEST);
     m_gl->ClearColor(0, 0, 0, 0);
-    m_gl->ColorMask(true, true, true, true);
+    m_gl->ColorMask(true, true, true, !requiresRGBEmulation());
 
     GLbitfield clearMask = GL_COLOR_BUFFER_BIT;
     if (!!m_depthStencilBuffer) {
@@ -764,6 +799,7 @@ bool DrawingBuffer::reset(const IntSize& newSize, bool wantDepthOrStencilBuffer)
     }
 
     clearFramebuffers(clearMask);
+    m_gl->ColorMask(true, true, true, true);

[Ken Russell (switch to Gerrit), 2016/04/29 09:33:09]

Were callers relying on this to set the color mask to (true, true, true, true)?
If so then maybe that should be made more explicit in the callers.

[erikchen, 2016/05/03 22:58:07]

No. I removed this call.

     return true;
 }
 
@@ -779,7 +815,36 @@ void DrawingBuffer::commit()
         int width = m_size.width();
         int height = m_size.height();
         // Use NEAREST, because there is no scale performed during the blit.
-        m_gl->BlitFramebufferCHROMIUM(0, 0, width, height, 0, 0, width, height, GL_COLOR_BUFFER_BIT, GL_NEAREST);
+        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_multisampleIntermediateFBO) {
+                DCHECK(!m_multisampleIntermediateRenderbuffer);

[Zhenyao Mo, 2016/04/29 22:54:16]

These two names are misleading.  The intermediate render buffer isn't
multi-sampled, so maybe just name it m_intermediateRenderbuffer,
m_intermediateFBO?

[erikchen, 2016/05/03 22:58:08]

Done.

+                m_gl->GenRenderbuffers(1, &m_multisampleIntermediateRenderbuffer);
+                m_gl->BindRenderbuffer(GL_RENDERBUFFER, m_multisampleIntermediateRenderbuffer);

[Ken Russell (switch to Gerrit), 2016/04/29 09:33:09]

Is resizing of m_multisampleIntermediateRenderbuffer handled properly during
resizes of the DrawingBuffer? It looks like this might have been missed in
DrawingBuffer::reset(). If it's missed, let's add a WebGL conformance test to
catch the error.

[erikchen, 2016/05/03 22:58:07]

No, it wasn't. I added a test:
https://codereview.appspot.com/294490043/

+                m_gl->RenderbufferStorage(GL_RENDERBUFFER, GL_RGB8, width, height);
+
+                m_gl->GenFramebuffers(1, &m_multisampleIntermediateFBO);
+                m_gl->BindFramebuffer(GL_DRAW_FRAMEBUFFER_ANGLE, m_multisampleIntermediateFBO);
+                m_gl->FramebufferRenderbuffer(GL_DRAW_FRAMEBUFFER_ANGLE, GL_COLOR_ATTACHMENT0, GL_RENDERBUFFER, m_multisampleIntermediateRenderbuffer);
+                m_gl->BindRenderbuffer(GL_RENDERBUFFER, m_renderbufferBinding);
+            }
+
+            m_gl->BindFramebuffer(GL_DRAW_FRAMEBUFFER_ANGLE, m_multisampleIntermediateFBO);
+            m_gl->BlitFramebufferCHROMIUM(0, 0, width, height, 0, 0, width, height, GL_COLOR_BUFFER_BIT, filter);
+
+            m_gl->BindFramebuffer(GL_READ_FRAMEBUFFER_ANGLE, m_multisampleIntermediateFBO);
+            m_gl->BindFramebuffer(GL_DRAW_FRAMEBUFFER_ANGLE, m_fbo);
+        }
+
+        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);
@@ -933,21 +998,32 @@ void DrawingBuffer::deleteChromiumImageForTexture(TextureInfo* info)
     }
 }
 
-DrawingBuffer::TextureInfo DrawingBuffer::createTextureAndAllocateMemory(const IntSize& size)
+void DrawingBuffer::clearChromiumImageIfNecessary(const TextureInfo& info)
 {
-    // TODO(erikchen): Add support for a CHROMIUM_image back buffer whose
-    // behavior mimics a texture with internal format GL_RGB.
-    // https://crbug.com/581777.
-    if (!m_wantAlphaChannel)
-        return createDefaultTextureAndAllocateMemory(size);
+    if (m_wantAlphaChannel)

[Zhenyao Mo, 2016/04/29 22:54:15]

You can also return early if we don't need to emulate, then the texture channels
will just be cleared lazily.

[erikchen, 2016/05/03 22:58:07]

Done.

+        return;
+
+    GLuint fbo = 0;
+    m_gl->GenFramebuffers(1, &fbo);
+    m_gl->BindFramebuffer(GL_FRAMEBUFFER, fbo);
+    m_gl->FramebufferTexture2D(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, info.parameters.target, info.textureId, 0);
+    m_gl->ClearColor(0, 0, 0, 1);
+    m_gl->ColorMask(false, false, false, true);

[Ken Russell (switch to Gerrit), 2016/04/29 09:33:09]

Is it deliberate that only the alpha channel is being cleared (to 1.0) here? If
so I'd suggest making this more explicit in either the name of this method or
its documentation in the header. (I'm guessing this is the only place in the
code which is allowed to touch the alpha channel for the emulated RGB back
buffers, and the clearIfComposited code path takes care of clearing the RGB
channels.)

[erikchen, 2016/05/03 22:58:07]

Yes. I updated the name of this method to be clearChromiumImageAlpha, and also
updated the documentation.

+    m_gl->Clear(GL_COLOR_BUFFER_BIT);
+    m_gl->FramebufferTexture2D(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, info.parameters.target, 0, 0);
+    m_gl->DeleteFramebuffers(1, &fbo);
+    restoreFramebufferBindings();

[Zhenyao Mo, 2016/04/29 22:54:16]

Should we also restore clear color and clear mask at the end?

[erikchen, 2016/05/03 22:58:07]

Yes. Done.

+}
 
+DrawingBuffer::TextureInfo DrawingBuffer::createTextureAndAllocateMemory(const IntSize& size)
+{
     if (!RuntimeEnabledFeatures::webGLImageChromiumEnabled())
         return createDefaultTextureAndAllocateMemory(size);
 
     // First, try to allocate a CHROMIUM_image. This always has the potential to
     // fail.
     TextureParameters parameters = chromiumImageTextureParameters();
-    GLuint imageId = m_gl->CreateGpuMemoryBufferImageCHROMIUM(size.width(), size.height(), parameters.internalColorFormat, GC3D_SCANOUT_CHROMIUM);
+    GLuint imageId = m_gl->CreateGpuMemoryBufferImageCHROMIUM(size.width(), size.height(), parameters.creationInternalColorFormat, GC3D_SCANOUT_CHROMIUM);
     if (!imageId)
         return createDefaultTextureAndAllocateMemory(size);
 
@@ -958,6 +1034,7 @@ DrawingBuffer::TextureInfo DrawingBuffer::createTextureAndAllocateMemory(const I
     info.textureId = textureId;
     info.imageId = imageId;
     info.parameters = parameters;
+    clearChromiumImageIfNecessary(info);
     return info;
 }
 
@@ -965,7 +1042,7 @@ DrawingBuffer::TextureInfo DrawingBuffer::createDefaultTextureAndAllocateMemory(
 {
     TextureParameters parameters = defaultTextureParameters();
     GLuint textureId = createColorTexture(parameters);
-    texImage2DResourceSafe(parameters.target, 0, parameters.internalColorFormat, size.width(), size.height(), 0, parameters.colorFormat, GL_UNSIGNED_BYTE);
+    texImage2DResourceSafe(parameters.target, 0, parameters.creationInternalColorFormat, size.width(), size.height(), 0, parameters.colorFormat, GL_UNSIGNED_BYTE);
 
     DrawingBuffer::TextureInfo info;
     info.textureId = textureId;
@@ -978,10 +1055,11 @@ void DrawingBuffer::resizeTextureMemory(TextureInfo* info, const IntSize& size)
     ASSERT(info->textureId);
     if (info->imageId) {
         deleteChromiumImageForTexture(info);
-        info->imageId = m_gl->CreateGpuMemoryBufferImageCHROMIUM(size.width(), size.height(), info->parameters.internalColorFormat, GC3D_SCANOUT_CHROMIUM);
+        info->imageId = m_gl->CreateGpuMemoryBufferImageCHROMIUM(size.width(), size.height(), info->parameters.creationInternalColorFormat, GC3D_SCANOUT_CHROMIUM);
         if (info->imageId) {
             m_gl->BindTexture(info->parameters.target, info->textureId);
             m_gl->BindTexImage2DCHROMIUM(info->parameters.target, info->imageId);
+            clearChromiumImageIfNecessary(*info);
             return;
         }
 
@@ -992,7 +1070,7 @@ void DrawingBuffer::resizeTextureMemory(TextureInfo* info, const IntSize& size)
     }
 
     m_gl->BindTexture(info->parameters.target, info->textureId);
-    texImage2DResourceSafe(info->parameters.target, 0, info->parameters.internalColorFormat, size.width(), size.height(), 0, info->parameters.colorFormat, GL_UNSIGNED_BYTE);
+    texImage2DResourceSafe(info->parameters.target, 0, info->parameters.creationInternalColorFormat, size.width(), size.height(), 0, info->parameters.colorFormat, GL_UNSIGNED_BYTE);
 }
 
 void DrawingBuffer::attachColorBufferToCurrentFBO()