Fix cull nesting assertion.

Cull rects are in local coordinates and cannot be compared directly.

No wonder it was so hard enforcing this in Blink :o

This moves the validation logic into SkCanvas, using a device-space
cull stack (debug build only).

There are still some Blink bugs causing violations, so for now I'd like
to keep this as an error message only.

R=reed@google.com, robertphillips@google.com

Author: fmalita@chromium.org

Review URL: https://codereview.chromium.org/200923008

git-svn-id: http://skia.googlecode.com/svn/trunk@13885 2bbb7eff-a529-9590-31e7-b0007b416f81

include/core/SkCanvas.h

@@ -1063,20 +1063,13 @@ public:
      *  is not enforced, but the information might be used to quick-reject command blocks,
      *  so an incorrect bounding box may result in incomplete rendering.
      */
-    void pushCull(const SkRect& cullRect) {
-        ++fCullCount;
-        this->onPushCull(cullRect);
-    }
+    void pushCull(const SkRect& cullRect);
 
     /**
      *  Terminates the current culling block, and restores the previous one (if any).
      */
-    void popCull() {
-        if (fCullCount > 0) {
-            --fCullCount;
-            this->onPopCull();
-        }
-    }
+    void popCull();
+
     //////////////////////////////////////////////////////////////////////////
 
     /** Get the current bounder object.
@@ -1394,6 +1387,9 @@ private:
     };
 
 #ifdef SK_DEBUG
+    // The cull stack rects are in device-space
+    SkTDArray<SkIRect> fCullStack;
+    void validateCull(const SkIRect&);
     void validateClip() const;
 #else
     void validateClip() const {}

src/core/SkCanvas.cpp

@@ -1161,6 +1161,60 @@ void SkCanvas::onPopCull() {
     // do nothing. Subclasses may do something
 }
 
+/////////////////////////////////////////////////////////////////////////////
+#ifdef SK_DEBUG
+// Ensure that cull rects are monotonically nested in device space.
+void SkCanvas::validateCull(const SkIRect& devCull) {
+    if (fCullStack.isEmpty()
+        || devCull.isEmpty()
+        || fCullStack.top().contains(devCull)) {
+        return;
+    }
+
+    SkDEBUGF(("Invalid cull: [%d %d %d %d] (previous cull: [%d %d %d %d])\n",
+              devCull.x(), devCull.y(), devCull.right(), devCull.bottom(),
+              fCullStack.top().x(), fCullStack.top().y(),
+              fCullStack.top().right(), fCullStack.top().bottom()));
+
+#ifdef ASSERT_NESTED_CULLING
+    SkDEBUGFAIL("Invalid cull.");
+#endif
+}
+#endif
+
+void SkCanvas::pushCull(const SkRect& cullRect) {
+    ++fCullCount;
+    this->onPushCull(cullRect);
+
+#ifdef SK_DEBUG
+    // Map the cull rect into device space.
+    SkRect mappedCull;
+    this->getTotalMatrix().mapRect(&mappedCull, cullRect);
+
+    // Take clipping into account.
+    SkIRect devClip, devCull;
+    mappedCull.roundOut(&devCull);
+    this->getClipDeviceBounds(&devClip);
+    if (!devCull.intersect(devClip)) {
+        devCull.setEmpty();
+    }
+
+    this->validateCull(devCull);
+    fCullStack.push(devCull); // balanced in popCull
+#endif
+}
+
+void SkCanvas::popCull() {
+    SkASSERT(fCullStack.count() == fCullCount);
+
+    if (fCullCount > 0) {
+        --fCullCount;
+        this->onPopCull();
+
+        SkDEBUGCODE(fCullStack.pop());
+    }
+}
+
 /////////////////////////////////////////////////////////////////////////////
 
 void SkCanvas::internalDrawBitmap(const SkBitmap& bitmap,

src/core/SkPictureRecord.cpp

@@ -1559,18 +1559,6 @@ void SkPictureRecord::endCommentGroup() {
 // [op/size] [rect] [skip offset]
 static const uint32_t kPushCullOpSize = 2 * kUInt32Size + sizeof(SkRect);
 void SkPictureRecord::onPushCull(const SkRect& cullRect) {
-    // Skip identical cull rects.
-    if (!fCullOffsetStack.isEmpty()) {
-        const SkRect& prevCull = fWriter.readTAt<SkRect>(fCullOffsetStack.top() - sizeof(SkRect));
-        if (prevCull == cullRect) {
-            // Skipped culls are tracked on the stack, but they point to the previous offset.
-            fCullOffsetStack.push(fCullOffsetStack.top());
-            return;
-        }
-
-        SkASSERT(prevCull.contains(cullRect));
-    }
-
     uint32_t size = kPushCullOpSize;
     size_t initialOffset = this->addDraw(PUSH_CULL, &size);
     // PUSH_CULL's size should stay constant (used to rewind).
@@ -1588,11 +1576,6 @@ void SkPictureRecord::onPopCull() {
     uint32_t cullSkipOffset = fCullOffsetStack.top();
     fCullOffsetStack.pop();
 
-    // Skipped push, do the same for pop.
-    if (!fCullOffsetStack.isEmpty() && cullSkipOffset == fCullOffsetStack.top()) {
-        return;
-    }
-
     // Collapse empty push/pop pairs.
     if ((size_t)(cullSkipOffset + kUInt32Size) == fWriter.bytesWritten()) {
         SkASSERT(fWriter.bytesWritten() >= kPushCullOpSize);