Make the canvas draw looper internal layer not part of SkCanvas save count

src/core/SkCanvas.cpp

Index: src/core/SkCanvas.cpp
diff --git a/src/core/SkCanvas.cpp b/src/core/SkCanvas.cpp
index 8426f090ec5949653ab516ffca3f7d33a317c338..8fe572010b5872dad067848cc3e155c1a3b0d53d 100644
--- a/src/core/SkCanvas.cpp
+++ b/src/core/SkCanvas.cpp
@@ -198,23 +198,25 @@ public:
     DeviceCM*       fTopLayer;
     SkRasterClip    fRasterClip;
     SkMatrix        fMatrix;
-    int             fDeferredSaveCount;
+    int             fSaveCount;  // The count of SkCanvas::save() calls when this rec was created.
 
-    MCRec(bool conservativeRasterClip) : fRasterClip(conservativeRasterClip) {
+    MCRec(bool conservativeRasterClip, int saveCount)
+            : fRasterClip(conservativeRasterClip)
+            , fSaveCount(saveCount) {
         fFilter     = NULL;
         fLayer      = NULL;
         fTopLayer   = NULL;
         fMatrix.reset();
-        fDeferredSaveCount = 0;
 
         // don't bother initializing fNext
         inc_rec();
     }
-    MCRec(const MCRec& prev) : fRasterClip(prev.fRasterClip), fMatrix(prev.fMatrix) {
+    MCRec(const MCRec& prev, int saveCount)
+            : fRasterClip(prev.fRasterClip), fMatrix(prev.fMatrix)
+            , fSaveCount(saveCount) {
         fFilter = SkSafeRef(prev.fFilter);
         fLayer = NULL;
         fTopLayer = prev.fTopLayer;
-        fDeferredSaveCount = 0;
 
         // don't bother initializing fNext
         inc_rec();
@@ -436,7 +438,7 @@ SkBaseDevice* SkCanvas::init(SkBaseDevice* device, InitFlags flags) {
     fMetaData = NULL;
 
     fMCRec = (MCRec*)fMCStack.push_back();
-    new (fMCRec) MCRec(fConservativeRasterClip);
+    new (fMCRec) MCRec(fConservativeRasterClip, fSaveCount);
 
     fMCRec->fLayer = SkNEW_ARGS(DeviceCM, (NULL, NULL, NULL, fConservativeRasterClip));
     fMCRec->fTopLayer = fMCRec->fLayer;
@@ -545,7 +547,6 @@ SkCanvas::SkCanvas(const SkBitmap& bitmap)
 SkCanvas::~SkCanvas() {
     // free up the contents of our deque
     this->restoreToCount(1);    // restore everything but the last
-
     this->internalRestore();    // restore the last, since we're going away
 
     SkDELETE(fMetaData);
@@ -752,31 +753,17 @@ void SkCanvas::updateDeviceCMCache() {
 ///////////////////////////////////////////////////////////////////////////////
 
 void SkCanvas::checkForDeferredSave() {
-    if (fMCRec->fDeferredSaveCount > 0) {
-        fMCRec->fDeferredSaveCount -= 1;
+    if (fMCRec->fSaveCount < fSaveCount) {
         this->doSave();
     }
 }
 
 int SkCanvas::getSaveCount() const {
-#ifdef SK_DEBUG
-    int count = 0;
-    SkDeque::Iter iter(fMCStack, SkDeque::Iter::kFront_IterStart);
-    for (;;) {
-        const MCRec* rec = (const MCRec*)iter.next();
-        if (!rec) {
-            break;
-        }
-        count += 1 + rec->fDeferredSaveCount;
-    }
-    SkASSERT(count == fSaveCount);
-#endif
     return fSaveCount;
 }
 
 int SkCanvas::save() {
     fSaveCount += 1;
-    fMCRec->fDeferredSaveCount += 1;
     return this->getSaveCount() - 1;  // return our prev value
 }
 
@@ -786,20 +773,23 @@ void SkCanvas::doSave() {
 }
 
 void SkCanvas::restore() {
-    if (fMCRec->fDeferredSaveCount > 0) {
-        SkASSERT(fSaveCount > 1);
-        fSaveCount -= 1;
-        fMCRec->fDeferredSaveCount -= 1;
-    } else {
-        // check for underflow
+    int deferredSaveCount = fSaveCount - fMCRec->fSaveCount;
+    SkASSERT(deferredSaveCount >= 0);
+    if (deferredSaveCount == 0) {
+        // Check if the client tried to restore() too many times.
         if (fMCStack.count() > 1) {
             this->willRestore();
-            SkASSERT(fSaveCount > 1);
-            fSaveCount -= 1;
             this->internalRestore();
+            fSaveCount -= 1;
             this->didRestore();
         }
+    } else {
+        // The topmost save was deferred.
+        fSaveCount -= 1;
     }
+
+    // Note: we can not detect the case where errorneous SkCanvas::restore()
+    // is called within the SkDrawLooper callback.
 }
 
 void SkCanvas::restoreToCount(int count) {
@@ -816,9 +806,8 @@ void SkCanvas::restoreToCount(int count) {
 
 void SkCanvas::internalSave() {
     MCRec* newTop = (MCRec*)fMCStack.push_back();
-    new (newTop) MCRec(*fMCRec);    // balanced in restore()
+    new (newTop) MCRec(*fMCRec, fSaveCount);    // balanced in restore()
     fMCRec = newTop;
-
     fClipStack->save();
 }
 
@@ -879,7 +868,7 @@ int SkCanvas::saveLayer(const SkRect* bounds, const SkPaint* paint) {
         bounds = NULL;
     }
     SaveLayerStrategy strategy = this->willSaveLayer(bounds, paint, kARGB_ClipLayer_SaveFlag);
-    fSaveCount += 1;
+    fSaveCount++;
     this->internalSaveLayer(bounds, paint, kARGB_ClipLayer_SaveFlag, strategy);
     return this->getSaveCount() - 1;
 }
@@ -889,7 +878,7 @@ int SkCanvas::saveLayer(const SkRect* bounds, const SkPaint* paint, SaveFlags fl
         bounds = NULL;
     }
     SaveLayerStrategy strategy = this->willSaveLayer(bounds, paint, flags);
-    fSaveCount += 1;
+    fSaveCount++;
     this->internalSaveLayer(bounds, paint, flags, strategy);
     return this->getSaveCount() - 1;
 }
@@ -977,6 +966,7 @@ int SkCanvas::saveLayerAlpha(const SkRect* bounds, U8CPU alpha,
 
 void SkCanvas::internalRestore() {
     SkASSERT(fMCStack.count() != 0);
+    SkASSERT(fMCRec->fSaveCount == fSaveCount);
 
     fDeviceCMDirty = true;
     fCachedLocalClipBoundsDirty = true;
@@ -1007,6 +997,7 @@ void SkCanvas::internalRestore() {
         }
         SkDELETE(layer);
     }
+    SkASSERT(fMCStack.count() == 0 || fMCRec->fSaveCount <= fSaveCount);
 }
 
 SkSurface* SkCanvas::newSurface(const SkImageInfo& info, const SkSurfaceProps* props) {