update skpdiff visualization (image magnification with alpha mask)

tools/skpdiff/SkDifferentPixelsMetric_cpu.cpp

Index: tools/skpdiff/SkDifferentPixelsMetric_cpu.cpp
diff --git a/tools/skpdiff/SkDifferentPixelsMetric_cpu.cpp b/tools/skpdiff/SkDifferentPixelsMetric_cpu.cpp
index 4e5e93969c3f743ecc6024bbba9576a06a3791ef..d09394f9b0491fb9641dec63f9252c8e6a2d1089 100644
--- a/tools/skpdiff/SkDifferentPixelsMetric_cpu.cpp
+++ b/tools/skpdiff/SkDifferentPixelsMetric_cpu.cpp
@@ -16,6 +16,7 @@ struct SkDifferentPixelsMetric::QueuedDiff {
     bool finished;
     double result;
     SkTDArray<SkIPoint>* poi;
+    SkBitmap poiAlphaMask;
 };
 
 const char* SkDifferentPixelsMetric::getName() {
@@ -44,6 +45,14 @@ int SkDifferentPixelsMetric::queueDiff(SkBitmap* baseline, SkBitmap* test) {
     int height = baseline->height();
     int differentPixelsCount = 0;
 
+    // Prepare the POI alpha mask if needed
+    if (fPOIAlphaMask) {

[epoger, 2013/10/21 15:02:53]

Where is fPOIAlphaMask declared?  I don't see it in SkDiffContext.h

Oh, I see, it's in the SkImageDiffer class declaration, not the
SkDifferentPixelsMetric class declaration (and SkDifferentPixelsMetric extends
SkImageDiffer).  Since it's only used in SkDifferentPixelsMetric, wouldn't it be
better to declare it as part of that class?

+        diff->poiAlphaMask.setConfig(SkBitmap::kA8_Config, width, height);
+        diff->poiAlphaMask.allocPixels();
+        diff->poiAlphaMask.lockPixels();
+        diff->poiAlphaMask.eraseARGB(SK_AlphaOPAQUE, 0, 0, 0);
+    }
+
     // Prepare the pixels for comparison
     baseline->lockPixels();
     test->lockPixels();
@@ -56,6 +65,9 @@ int SkDifferentPixelsMetric::queueDiff(SkBitmap* baseline, SkBitmap* test) {
             if (std::memcmp(&baselineRow[x * 4], &testRow[x * 4], 4) != 0) {
                 poi->push()->set(x, y);
                 differentPixelsCount++;
+                if (fPOIAlphaMask) {
+                    *diff->poiAlphaMask.getAddr8(x,y) = SK_AlphaTRANSPARENT;
+                }
             }
         }
     }
@@ -93,3 +105,10 @@ int SkDifferentPixelsMetric::getPointsOfInterestCount(int id) {
 SkIPoint* SkDifferentPixelsMetric::getPointsOfInterest(int id) {
     return fQueuedDiffs[id].poi->begin();
 }
+
+SkBitmap* SkDifferentPixelsMetric::getPointsOfInterestAlphaMask(int id) {
+    if (fQueuedDiffs[id].poiAlphaMask.empty()) {
+        return NULL;
+    }
+    return &fQueuedDiffs[id].poiAlphaMask;
+}