Allow DrawingBuffer to present to a bitmap.

Source/core/platform/graphics/gpu/DrawingBuffer.cpp

Index: Source/core/platform/graphics/gpu/DrawingBuffer.cpp
diff --git a/Source/core/platform/graphics/gpu/DrawingBuffer.cpp b/Source/core/platform/graphics/gpu/DrawingBuffer.cpp
index 5940b06e7cd3d5cea867b30fbcc6f362f075d436..4ca8b0fa727e3aedbce5cab54f775f5a99bd2bc2 100644
--- a/Source/core/platform/graphics/gpu/DrawingBuffer.cpp
+++ b/Source/core/platform/graphics/gpu/DrawingBuffer.cpp
@@ -176,7 +176,7 @@ WebKit::WebGraphicsContext3D* DrawingBuffer::context()
     return m_context->webContext();
 }
 
-bool DrawingBuffer::prepareMailbox(WebKit::WebExternalTextureMailbox* outMailbox)
+bool DrawingBuffer::prepareMailbox(WebKit::WebExternalTextureMailbox* outMailbox, bool bitmap)
 {
     if (!m_context || !m_contentsChanged || !m_lastColorBuffer)
         return false;
@@ -187,6 +187,32 @@ bool DrawingBuffer::prepareMailbox(WebKit::WebExternalTextureMailbox* outMailbox
     if (multisample())
         commit();
 
+    if (bitmap) {
+        SkBitmap* bitmap = &m_lastColorBuffer->mailbox.bitmap;
+        m_context->bindFramebuffer(GraphicsContext3D::FRAMEBUFFER, m_fbo);
+        if (bitmap->width() != size().width()
+            || bitmap->height() != size().height()) {
+            bitmap->setConfig(SkBitmap::kARGB_8888_Config, size().width(), size().height(), 0);
+            bitmap->allocPixels();
+        }
+        m_lastColorBuffer->mailbox.size = size();
+
+        SkAutoLockPixels bitmapLock(*bitmap);
+
+        unsigned char* pixels = static_cast<unsigned char*>(bitmap->getPixels());
+        m_context->readPixels(0, 0, size().width(), size().height(), GraphicsContext3D::RGBA, GraphicsContext3D::UNSIGNED_BYTE, pixels);

[Ken Russell (switch to Gerrit), 2013/06/27 13:41:02]

We'd better be careful that the user hasn't set the unpack alignment to 8.

+        for (int i = 0; i < size().width() * size().height() * 4; i += 4)
+            swap(pixels[i + 0], pixels[i + 2]);

[Ken Russell (switch to Gerrit), 2013/06/27 13:41:02]

I'm pretty sure this needs to be conditional depending on the platform. See
GraphicsContext3D::paintRenderingResultsToImageData . If there's a possibility
for code reuse that would be better.

+
+        if (m_attributes.alpha && !m_attributes.premultipliedAlpha) {
+            for (int i = 0; i < size().width() * size().height() * 4; i += 4) {
+                pixels[i + 0] = std::min(255, pixels[i + 0] * pixels[i + 3] / 255);
+                pixels[i + 1] = std::min(255, pixels[i + 1] * pixels[i + 3] / 255);
+                pixels[i + 2] = std::min(255, pixels[i + 2] * pixels[i + 3] / 255);
+            }
+        }
+    }
+
     // We must restore the texture binding since creating new textures,
     // consuming and producing mailboxes changes it.
     ScopedTextureUnit0BindingRestorer restorer(m_context.get(), m_activeTextureUnit, m_texture2DBinding);
@@ -216,6 +242,10 @@ bool DrawingBuffer::prepareMailbox(WebKit::WebExternalTextureMailbox* outMailbox
     } else {
         Extensions3D* extensions = m_context->getExtensions();
         extensions->copyTextureCHROMIUM(GraphicsContext3D::TEXTURE_2D, m_colorBuffer, nextFrontColorBuffer->textureId, 0, GraphicsContext3D::RGBA, GraphicsContext3D::UNSIGNED_BYTE);
+        SkBitmap nextBitmap = nextFrontColorBuffer->mailbox.bitmap;
+        nextFrontColorBuffer->mailbox.bitmap = m_lastColorBuffer->mailbox.bitmap;
+        nextFrontColorBuffer->mailbox.size = m_lastColorBuffer->mailbox.size;
+        m_lastColorBuffer->mailbox.bitmap = nextBitmap;
     }
 
     if (multisample() && !m_framebufferBinding)
@@ -231,6 +261,7 @@ bool DrawingBuffer::prepareMailbox(WebKit::WebExternalTextureMailbox* outMailbox
     m_context->markLayerComposited();
 
     *outMailbox = nextFrontColorBuffer->mailbox;
+
     m_frontColorBuffer = nextFrontColorBuffer->textureId;
     return true;
 }
@@ -238,12 +269,13 @@ bool DrawingBuffer::prepareMailbox(WebKit::WebExternalTextureMailbox* outMailbox
 void DrawingBuffer::mailboxReleased(const WebKit::WebExternalTextureMailbox& mailbox)
 {
     for (size_t i = 0; i < m_textureMailboxes.size(); i++) {
-         RefPtr<MailboxInfo> mailboxInfo = m_textureMailboxes[i];
-         if (!memcmp(mailboxInfo->mailbox.name, mailbox.name, sizeof(mailbox.name))) {
-             mailboxInfo->mailbox.syncPoint = mailbox.syncPoint;
-             m_recycledMailboxes.append(mailboxInfo.release());
-             return;
-         }
+        RefPtr<MailboxInfo> mailboxInfo = m_textureMailboxes[i];
+        if (!memcmp(mailboxInfo->mailbox.name, mailbox.name, sizeof(mailbox.name))) {
+            mailboxInfo->mailbox.syncPoint = mailbox.syncPoint;
+            mailboxInfo->mailbox.bitmap = mailbox.bitmap;
+            m_recycledMailboxes.append(mailboxInfo.release());
+            return;
+        }
      }
      ASSERT_NOT_REACHED();
 }