WebGL 2: add read/write framebuffer binding points to related APIs

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 117 matching lines @@
 DrawingBuffer::DrawingBuffer(PassOwnPtr<WebGraphicsContext3D> context,
     PassOwnPtr<Extensions3DUtil> extensionsUtil,
     bool multisampleExtensionSupported,
     bool packedDepthStencilExtensionSupported,
     bool discardFramebufferSupported,
     PreserveDrawingBuffer preserve,
     WebGraphicsContext3D::Attributes requestedAttributes)
     : m_preserveDrawingBuffer(preserve)
     , m_scissorEnabled(false)
     , m_texture2DBinding(0)
-    , m_framebufferBinding(0)
+    , m_drawFramebufferBinding(0)
+    , m_readFramebufferBinding(0)
     , m_activeTextureUnit(GL_TEXTURE0)
     , m_context(context)
     , m_extensionsUtil(extensionsUtil)
     , m_size(-1, -1)
     , m_requestedAttributes(requestedAttributes)
     , m_multisampleExtensionSupported(multisampleExtensionSupported)
     , m_packedDepthStencilExtensionSupported(packedDepthStencilExtensionSupported)
     , m_discardFramebufferSupported(discardFramebufferSupported)
     , m_fbo(0)
     , m_depthStencilBuffer(0)
@@ skipping 93 matching lines @@
         // 3. Javascript makes a context lost using WEBGL_lose_context extension.
         // 4. Here.
         return false;
     }
     ASSERT(!m_isHidden);
     if (!m_contentsChanged)
         return false;
 
     // Resolve the multisampled buffer into m_colorBuffer texture.
     if (m_multisampleMode != None)
-        commit();
+        commit(GL_FRAMEBUFFER);
 
     if (bitmap) {
         bitmap->setSize(size());
 
         unsigned char* pixels = bitmap->pixels();
         bool needPremultiply = m_actualAttributes.alpha && !m_actualAttributes.premultipliedAlpha;
         WebGLImageConversion::AlphaOp op = needPremultiply ? WebGLImageConversion::AlphaDoPremultiply : WebGLImageConversion::AlphaDoNothing;
         if (pixels)
             readBackFramebuffer(pixels, size().width(), size().height(), ReadbackSkia, op);
     }
@@ skipping 31 matching lines @@
 
         if (m_discardFramebufferSupported) {
             // Explicitly discard framebuffer to save GPU memory bandwidth for tile-based GPU arch.
             const WGC3Denum attachments[3] = { GL_COLOR_ATTACHMENT0, GL_DEPTH_ATTACHMENT, GL_STENCIL_ATTACHMENT};
             m_context->discardFramebufferEXT(GL_FRAMEBUFFER, 3, attachments);
         }
     } else {
         m_context->copyTextureCHROMIUM(GL_TEXTURE_2D, m_colorBuffer.textureId, frontColorBufferMailbox->textureInfo.textureId, GL_RGBA, GL_UNSIGNED_BYTE);
     }
 
-    restoreFramebufferBinding();
+    restoreFramebufferBindings();
     m_contentsChanged = false;
 
     m_context->produceTextureDirectCHROMIUM(frontColorBufferMailbox->textureInfo.textureId, GL_TEXTURE_2D, frontColorBufferMailbox->mailbox.name);
     m_context->flush();
     frontColorBufferMailbox->mailbox.syncPoint = m_context->insertSyncPoint();
     frontColorBufferMailbox->mailbox.allowOverlay = frontColorBufferMailbox->textureInfo.imageId != 0;
     setBufferClearNeeded(true);
 
     // set m_parentDrawingBuffer to make sure 'this' stays alive as long as it has live mailboxes
     ASSERT(!frontColorBufferMailbox->m_parentDrawingBuffer);
@@ skipping 154 matching lines @@
     }
     m_actualAttributes.antialias = multisample();
     return true;
 }
 
 bool DrawingBuffer::copyToPlatformTexture(WebGraphicsContext3D* context, Platform3DObject texture, GLenum internalFormat,
     GLenum destType, GLint level, bool premultiplyAlpha, bool flipY, SourceDrawingBuffer sourceBuffer)
 {
     if (m_contentsChanged) {
         if (m_multisampleMode != None) {
-            commit();
-            restoreFramebufferBinding();
+            commit(GL_FRAMEBUFFER);
+            restoreFramebufferBindings();
         }
         m_context->flush();
     }
 
     if (!Extensions3DUtil::canUseCopyTextureCHROMIUM(GL_TEXTURE_2D, internalFormat, destType, level))
         return false;
 
     // Contexts may be in a different share group. We must transfer the texture through a mailbox first
     WebExternalTextureMailbox mailbox;
     GLint textureId = 0;
@@ skipping 297 matching lines @@
     if (m_actualAttributes.stencil) {
         m_context->clearStencil(0);
         clearMask |= GL_STENCIL_BUFFER_BIT;
         m_context->stencilMaskSeparate(GL_FRONT, 0xFFFFFFFF);
     }
 
     clearFramebuffers(clearMask);
     return true;
 }
 
-void DrawingBuffer::commit()
+void DrawingBuffer::commit(GLenum target)
 {
     if (m_multisampleFBO && !m_contentsChangeCommitted) {
         m_context->bindFramebuffer(GL_READ_FRAMEBUFFER_ANGLE, m_multisampleFBO);
         m_context->bindFramebuffer(GL_DRAW_FRAMEBUFFER_ANGLE, m_fbo);
 
         if (m_scissorEnabled)
             m_context->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.
         m_context->blitFramebufferCHROMIUM(0, 0, width, height, 0, 0, width, height, GL_COLOR_BUFFER_BIT, GL_NEAREST);
 
         if (m_scissorEnabled)
             m_context->enable(GL_SCISSOR_TEST);
     }
 
-    m_context->bindFramebuffer(GL_FRAMEBUFFER, m_fbo);
+    m_context->bindFramebuffer(target, m_fbo);

[yunchao, 2015/06/10 09:42:30]

WebGL conformance tests show that this code snippet lead to some failures. I
rethink of it, found that we should bound the framebuffer to m_fbo for
reading(glReadPixels, glCopyTexImage2D, etc), instead of using
restoreFramebufferBindings(), who bind to m_multisampleFBO. 

The data in multisampled FB has been blit-ed to single-sampled buffer, we should
read from the single-sampled buffer afterwards. That is the reason why we need
this function (DrawingBuffer::commit).

And the failures in WebGL conformance tests go away now.

     m_contentsChangeCommitted = true;
 }
 
-void DrawingBuffer::restoreFramebufferBinding()
+void DrawingBuffer::restoreFramebufferBindings()
 {
-    if (!m_framebufferBinding) {
-        bind();
+    if (m_drawFramebufferBinding && m_readFramebufferBinding) {
+        if (m_drawFramebufferBinding == m_readFramebufferBinding) {
+            m_context->bindFramebuffer(GL_FRAMEBUFFER, m_readFramebufferBinding);
+        } else {
+            m_context->bindFramebuffer(GL_READ_FRAMEBUFFER, m_readFramebufferBinding);
+            m_context->bindFramebuffer(GL_DRAW_FRAMEBUFFER, m_drawFramebufferBinding);
+        }
         return;
     }
-    m_context->bindFramebuffer(GL_FRAMEBUFFER, m_framebufferBinding);
+    if (!m_drawFramebufferBinding && !m_readFramebufferBinding) {
+        bind(GL_FRAMEBUFFER);
+        return;
+    }
+    if (!m_drawFramebufferBinding) {
+        bind(GL_DRAW_FRAMEBUFFER);
+        m_context->bindFramebuffer(GL_READ_FRAMEBUFFER, m_readFramebufferBinding);
+    } else {
+        bind(GL_READ_FRAMEBUFFER);
+        m_context->bindFramebuffer(GL_DRAW_FRAMEBUFFER, m_drawFramebufferBinding);
+    }
 }
 
 bool DrawingBuffer::multisample() const
 {
     return m_multisampleMode != None;
 }
 
 void DrawingBuffer::bind(GLenum target)
 {
-    m_context->bindFramebuffer(target, m_multisampleFBO ? m_multisampleFBO : m_fbo);
+    if (target != GL_READ_FRAMEBUFFER)
+        m_context->bindFramebuffer(target, m_multisampleFBO ? m_multisampleFBO : m_fbo);
+    else
+        m_context->bindFramebuffer(target, m_fbo);
 }
 
 void DrawingBuffer::setPackAlignment(GLint param)
 {
     m_packAlignment = param;
 }
 
 void DrawingBuffer::paintRenderingResultsToCanvas(ImageBuffer* imageBuffer)
 {
     paintFramebufferToCanvas(framebuffer(), size().width(), size().height(), !m_actualAttributes.premultipliedAlpha, imageBuffer);
@@ skipping 23 matching lines @@
     }
 
     readBackFramebuffer(static_cast<unsigned char*>(pixels.data()), width, height, ReadbackRGBA, WebGLImageConversion::AlphaDoNothing);
     flipVertically(static_cast<uint8_t*>(pixels.data()), width, height);
 
     if (fbo) {
         m_context->framebufferTexture2D(GL_FRAMEBUFFER, GL_COLOR_ATTACHMENT0, GL_TEXTURE_2D, 0, 0);
         m_context->deleteFramebuffer(fbo);
     }
 
-    restoreFramebufferBinding();
+    restoreFramebufferBindings();
 
     pixels.transfer(contents);
     return true;
 }
 
 void DrawingBuffer::paintFramebufferToCanvas(int framebuffer, int width, int height, bool premultiplyAlpha, ImageBuffer* imageBuffer)
 {
     unsigned char* pixels = 0;
 
     const SkBitmap& canvasBitmap = imageBuffer->bitmap();
@@ skipping 103 matching lines @@
 void DrawingBuffer::deleteChromiumImageForTexture(TextureInfo* info)
 {
     if (info->imageId) {
         m_context->releaseTexImage2DCHROMIUM(GL_TEXTURE_2D, info->imageId);
         m_context->destroyImageCHROMIUM(info->imageId);
         info->imageId = 0;
     }
 }
 
 } // namespace blink