Culling API

include/core/SkCanvas.h

Index: include/core/SkCanvas.h
diff --git a/include/core/SkCanvas.h b/include/core/SkCanvas.h
index 7235efb2f0a9cd3b23132541d9c695b0c81e1704..b427c4045ce452f367b261932c07b7bfbc54d9d5 100644
--- a/include/core/SkCanvas.h
+++ b/include/core/SkCanvas.h
@@ -891,7 +891,27 @@ public:
         // do nothing. Subclasses may do something
     }
 
+    /**
+     *  This call asserts that subsequent draw operations (up to the matching popCull() call)
+     *  are fully contained within the given bounding box. The assertion 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 += 1;
+        this->onPushCull(cullRect);
+    }
 
+    /**
+     *  Terminates the current culling block, and restores the previous one (if any).
+     */
+    void popCull() {
+        SkASSERT(fCullCount > 0);
+        if (fCullCount > 0) {

[caryclark, 2014/02/14 14:54:35]

since you have the assert, do you also need the test?
(I assume that we're not trying to make Skia fault-resistant, but maybe I assume
incorrectly)

[f(malita), 2014/02/20 02:37:26]

We guard against underflow for restore(), so I figured we should do the same
here. OTOH underflow is a client error, maybe there's value in signaling the
condition for debug builds?

It does seem inconsistent though, so I should probably remove the assert.

+            fCullCount -= 1;
+            this->onPopCull();
+        }
+    }

[reed1, 2014/02/14 14:39:06]

I wonder if we'll want similar helpers to what save/restore offers...

int pushCull returns its count
popCullToCount(int count) -- to pop all the way back to a specific count

Not asking for it, but just noticing

     //////////////////////////////////////////////////////////////////////////
 
     /** Get the current bounder object.
@@ -1053,6 +1073,9 @@ protected:
      */
     virtual SkBaseDevice* setDevice(SkBaseDevice* device);
 
+    virtual void onPushCull(const SkRect& cullRect);
+    virtual void onPopCull();
+
 private:
     class MCRec;
 
@@ -1065,6 +1088,7 @@ private:
 
     SkBounder*  fBounder;
     int         fSaveLayerCount;    // number of successful saveLayer calls
+    unsigned    fCullCount;         // number of active culls

[reed1, 2014/02/14 14:39:06]

nit: int so we can notice negatives easier, and to match other counters

[f(malita), 2014/02/20 02:37:26]

Will do.

 
     SkMetaData* fMetaData;