Move code in isPaintOpaque from SkDeferredCanvas.cpp to SkPaintPriv

The purpose of this code move is to make it re-usable in order to implement
occlusion culling optimizations in SkPicture similar to what we have now
in SkDeferredCanvas.

BUG=https://code.google.com/p/chromium/issues/detail?id=164530
Review URL: https://codereview.appspot.com/7196046

git-svn-id: http://skia.googlecode.com/svn/trunk@7361 2bbb7eff-a529-9590-31e7-b0007b416f81

1 files changed, 78 insertions, 0 deletions

diff --git a/src/core/SkPaintPriv.cpp b/src/core/SkPaintPriv.cpp
new file mode 100644
index 0000000000..ce05389019
--- /dev/null
+++ b/src/core/SkPaintPriv.cpp
@@ -0,0 +1,78 @@
+/*
+ * Copyright 2013 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+#include "SkPaintPriv.h"
+
+#include "SkBitmap.h"
+#include "SkColorFilter.h"
+#include "SkPaint.h"
+#include "SkShader.h"
+
+bool isPaintOpaque(const SkPaint* paint,
+                   const SkBitmap* bmpReplacesShader) {
+    // TODO: SkXfermode should have a virtual isOpaque method, which would
+    // make it possible to test modes that do not have a Coeff representation.
+
+    if (!paint) {
+        return bmpReplacesShader ? bmpReplacesShader->isOpaque() : true;
+    }
+
+    SkXfermode::Coeff srcCoeff, dstCoeff;
+    if (SkXfermode::AsCoeff(paint->getXfermode(), &srcCoeff, &dstCoeff)){
+        if (SkXfermode::kDA_Coeff == srcCoeff || SkXfermode::kDC_Coeff == srcCoeff ||
+            SkXfermode::kIDA_Coeff == srcCoeff || SkXfermode::kIDC_Coeff == srcCoeff) {
+            return false;
+        }
+        switch (dstCoeff) {
+        case SkXfermode::kZero_Coeff:
+            return true;
+        case SkXfermode::kISA_Coeff:
+            if (paint->getAlpha() != 255) {
+                break;
+            }
+            if (bmpReplacesShader) {
+                if (!bmpReplacesShader->isOpaque()) {
+                    break;
+                }
+            } else if (paint->getShader() && !paint->getShader()->isOpaque()) {
+                break;
+            }
+            if (paint->getColorFilter() &&
+                ((paint->getColorFilter()->getFlags() &
+                SkColorFilter::kAlphaUnchanged_Flag) == 0)) {
+                break;
+            }
+            return true;
+        case SkXfermode::kSA_Coeff:
+            if (paint->getAlpha() != 0) {
+                break;
+            }
+            if (paint->getColorFilter() &&
+                ((paint->getColorFilter()->getFlags() &
+                SkColorFilter::kAlphaUnchanged_Flag) == 0)) {
+                break;
+            }
+            return true;
+        case SkXfermode::kSC_Coeff:
+            if (paint->getColor() != 0) { // all components must be 0
+                break;
+            }
+            if (bmpReplacesShader || paint->getShader()) {
+                break;
+            }
+            if (paint->getColorFilter() && (
+                (paint->getColorFilter()->getFlags() &
+                SkColorFilter::kAlphaUnchanged_Flag) == 0)) {
+                break;
+            }
+            return true;
+        default:
+            break;
+        }
+    }
+    return false;
+}