De-virtualize SkCanvas save/restore.

include/core/SkCanvas.h

Index: include/core/SkCanvas.h
diff --git a/include/core/SkCanvas.h b/include/core/SkCanvas.h
index 773df89d789843ee4ef5b042403c57136afb94e6..5ab41656d086949703bd6ad5f7edb6e2d13a4124 100644
--- a/include/core/SkCanvas.h
+++ b/include/core/SkCanvas.h
@@ -358,7 +358,7 @@ public:
                      by calls to save/restore.
         @return The value to pass to restoreToCount() to balance this save()
     */
-    virtual int save(SaveFlags flags = kMatrixClip_SaveFlag);
+    int save(SaveFlags flags = kMatrixClip_SaveFlag);
 
     /** This behaves the same as save(), but in addition it allocates an
         offscreen bitmap. All drawing calls are directed there, and only when
@@ -373,7 +373,7 @@ public:
         @param flags  LayerFlags
         @return The value to pass to restoreToCount() to balance this save()
     */
-    virtual int saveLayer(const SkRect* bounds, const SkPaint* paint,
+    int saveLayer(const SkRect* bounds, const SkPaint* paint,

[robertphillips, 2014/03/11 15:49:44]

line up?

[f(malita), 2014/03/11 16:38:08]

Done.

                           SaveFlags flags = kARGB_ClipLayer_SaveFlag);
 
     /** This behaves the same as save(), but in addition it allocates an
@@ -396,7 +396,7 @@ public:
         call.
         It is an error to call restore() more times than save() was called.
     */
-    virtual void restore();
+    void restore();
 
     /** Returns the number of matrix/clip states on the SkCanvas' private stack.
         This will equal # save() calls - # restore() calls + 1. The save count on
@@ -1178,6 +1178,14 @@ protected:
     // default impl defers to its device
     virtual const void* onPeekPixels(SkImageInfo*, size_t* rowBytes);
 
+    // Subclass save/restore notifiers. These are called *before* updating the canvas state.
+    // Overriders should call the corresponding INHERITED method up the inheritance chain.
+    // For onSaveLayer(), returning false suppresses full layer allocation (and forces
+    // the base impl to only perform a state save + bounds clip).
+    virtual void onSave(SaveFlags) { }

[reed1, 2014/03/11 15:49:39]

nit: lets always put the impl of virtuals in the .cpp, even if they're empty.

[f(malita), 2014/03/11 16:38:08]

Since we're always up-calling INHERITED::on* from derived classes (mostly for
consistency), I wanted to make sure these stay inlined (that's assuming they get
inlined in the first place, which I think they do when the call is
class-qualified). I'll gladly switch if we don't care about that.

[reed1, 2014/03/11 16:53:38]

I see your point, and I'm trying to recall all of the reasons I've heard against
inlining a virtual. 

+    virtual bool onSaveLayer(const SkRect*, const SkPaint*, SaveFlags) { return true; }
+    virtual void onRestore() { }
+
     virtual void onDrawDRRect(const SkRRect&, const SkRRect&, const SkPaint&);
 
     enum ClipEdgeStyle {
@@ -1277,7 +1285,7 @@ private:
                                 const SkRect& dst, const SkPaint* paint);
     void internalDrawPaint(const SkPaint& paint);
     int internalSaveLayer(const SkRect* bounds, const SkPaint* paint,
-                          SaveFlags, bool justForImageFilter);
+                          SaveFlags, bool justForImageFilter, bool skipLayer);

[reed1, 2014/03/11 15:49:39]

Can the caller(s) cleanly do whatever internalSaveLayer does, if the caller
knows it is going to pass false?

[f(malita), 2014/03/11 16:38:08]

They probably could, but they still have to signal the common impl that it
should change behavior (and don't allocate a layer). Are you thinking of not
calling internalSaveLayer at all in that case? That would save us a flag, but
would also introduce some duplication in the handful of derived classes that
actually care about it.

[reed1, 2014/03/11 16:53:38]

Are derived classes allowed to call internalSaveLayer?

     void internalDrawDevice(SkBaseDevice*, int x, int y, const SkPaint*);
 
     // shared by save() and saveLayer()