Fix saveLayer() with a pixel-moving filter vs SkBBoxHierarchyRecord / SkRecordDraw

src/core/SkRecordDraw.cpp

Index: src/core/SkRecordDraw.cpp
diff --git a/src/core/SkRecordDraw.cpp b/src/core/SkRecordDraw.cpp
index a14b0316955dd0b1c93448c1bcd2410c5f74bae8..c796386f209b7d6ab50a3ab62decaf2e273b1a93 100644
--- a/src/core/SkRecordDraw.cpp
+++ b/src/core/SkRecordDraw.cpp
@@ -160,6 +160,11 @@ private:
         const SkPaint* paint;  // Unowned.  If set, adjusts the bounds of all ops in this block.
     };
 
+    static bool PaintMayAffectTransparentBlack(const SkPaint* paint) {
+        // FIXME: this is very conservative
+        return paint && (paint->getImageFilter() || paint->getColorFilter());
+    }
+
     template <typename T> void updateCTM(const T&) { /* most ops don't change the CTM */ }
     void updateCTM(const Restore& op)   { fCTM = &op.matrix; }
     void updateCTM(const SetMatrix& op) { fCTM = &op.matrix; }
@@ -173,7 +178,8 @@ private:
     void updateClipBounds(const ClipRect& op)   { fCurrentClipBounds = op.devBounds; }
     void updateClipBounds(const ClipRegion& op) { fCurrentClipBounds = op.devBounds; }
     void updateClipBounds(const SaveLayer& op)  {
-        if (op.bounds) {
+        // Intersect the clip with the SaveLayer bounds, unless the paint affects transparent black.
+        if (op.bounds && !PaintMayAffectTransparentBlack(op.paint)) {

[mtklein, 2014/08/22 15:45:58]

Just reading again:

"Since the bounds we pass to saveLayer are in the pre-filtering
coordinate space, they aren't correct for determining the actual
device pixels touched by the saveLayer in this case."

Does the fact that I'm running bounds through adjustAndMap() (adjust for paint
affects, map back to indentity space) mean I can logically drop this part of the
change?

             fCurrentClipBounds.intersect(this->adjustAndMap(*op.bounds, op.paint));
         }
     }
@@ -208,15 +214,20 @@ private:
         // We're done the Save block.  Apply the block's bounds to all control ops inside it.
         SaveBounds sb;
         fSaveStack.pop(&sb);
+
+        // If the paint affects transparent black, we can't trust any of our calculated bounds.
+        const SkIRect& bounds =
+            PaintMayAffectTransparentBlack(sb.paint) ? fCurrentClipBounds : sb.bounds;
+
         while (sb.controlOps --> 0) {
-            this->popControl(sb.bounds);
+            this->popControl(bounds);
         }
 
         // This whole Save block may be part another Save block.
-        this->updateSaveBounds(sb.bounds);
+        this->updateSaveBounds(bounds);
 
         // If called from a real Restore (not a phony one for balance), it'll need the bounds.
-        return sb.bounds;
+        return bounds;
     }
 
     void pushControl() {