[CSS Blending] Implement mix-blend-mode in software.

Source/core/rendering/CompositingReasons.h

 // Copyright 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef CompositingReasons_h
 #define CompositingReasons_h
 
 #include "wtf/MathExtras.h"
 #include <stdint.h>
 
 namespace WebCore {
 
 const uint64_t CompositingReasonNone                                   = 0;
 
 // Intrinsic reasons that can be known right away by the layer
 const uint64_t CompositingReason3DTransform                            = UINT64_C(1) << 0;
 const uint64_t CompositingReasonVideo                                  = UINT64_C(1) << 1;
 const uint64_t CompositingReasonCanvas                                 = UINT64_C(1) << 2;
 const uint64_t CompositingReasonPlugin                                 = UINT64_C(1) << 3;
 const uint64_t CompositingReasonIFrame                                 = UINT64_C(1) << 4;
 const uint64_t CompositingReasonBackfaceVisibilityHidden               = UINT64_C(1) << 5;
 const uint64_t CompositingReasonAnimation                              = UINT64_C(1) << 6;
 const uint64_t CompositingReasonFilters                                = UINT64_C(1) << 7;
 const uint64_t CompositingReasonPositionFixed                          = UINT64_C(1) << 8;
 const uint64_t CompositingReasonPositionSticky                         = UINT64_C(1) << 9;
 const uint64_t CompositingReasonOverflowScrollingTouch                 = UINT64_C(1) << 10;
+
+// FIXME: remove the following compositing reason since it's no longer used.

[shawnsingh, 2013/09/10 21:23:40]

I think it's best to address this FIXME in this patch.   It should be possible
to remove it on the chromium side first to make this possible.

[mitica, 2013/09/11 16:04:14]

The only problem with this would be that removing the blending flag from
https://code.google.com/p/chromium/codesearch#chromium/src/cc/layers/composit...
would create a 1 bit gap in the reasons list.
This cannot be avoided due to the compile asserts in blink in
https://code.google.com/p/chromium/codesearch#chromium/src/webkit/renderer/co...

Anyhow, could you please have a look at https://codereview.chromium.org/23530026
first? After this is finished, I will be able to completely remove the blending
compositing reason on the blink side :)

 const uint64_t CompositingReasonBlending                               = UINT64_C(1) << 11;
 
 // Overlap reasons that require knowing what's behind you in paint-order before knowing the answer
 const uint64_t CompositingReasonAssumedOverlap                         = UINT64_C(1) << 12;
 const uint64_t CompositingReasonOverlap                                = UINT64_C(1) << 13;
 const uint64_t CompositingReasonNegativeZIndexChildren                 = UINT64_C(1) << 14;
 
 // Subtree reasons that require knowing what the status of your subtree is before knowing the answer
 const uint64_t CompositingReasonTransformWithCompositedDescendants     = UINT64_C(1) << 15;
 const uint64_t CompositingReasonOpacityWithCompositedDescendants       = UINT64_C(1) << 16;
@@ skipping 25 matching lines @@
 
 const uint64_t CompositingReasonLayerForVideoOverlay                   = UINT64_C(1) << 34;
 
 // Note: if you add more reasons here, you will need to update WebCompositingReasons as well.
 typedef uint64_t CompositingReasons;
 
 
 } // namespace WebCore
 
 #endif // CompositingReasons_h