Culling API

include/core/SkCanvas.h

 /*
  * Copyright 2006 The Android Open Source Project
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #ifndef SkCanvas_DEFINED
 #define SkCanvas_DEFINED
 
@@ skipping 873 matching lines @@
     virtual void beginCommentGroup(const char* description) {
         // do nothing. Subclasses may do something
     }
     virtual void addComment(const char* kywd, const char* value) {
         // do nothing. Subclasses may do something
     }
     virtual void endCommentGroup() {
         // 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.
         The bounder's reference count is unchaged.
         @return the canva's bounder (or NULL).
     */
     SkBounder*  getBounder() const { return fBounder; }
 
     /** Set a new bounder (or NULL).
         Pass NULL to clear any previous bounder.
@@ skipping 141 matching lines @@
      DEPRECATED -- need to remove when subclass stop relying on it.
      Marked as 'protected' to avoid new clients using this before we can
      completely remove it.
 
      Specify a device for this canvas to draw into. If it is not null, its
      reference count is incremented. If the canvas was already holding a
      device, its reference count is decremented. The new device is returned.
      */
     virtual SkBaseDevice* setDevice(SkBaseDevice* device);
 
+    virtual void onPushCull(const SkRect& cullRect);
+    virtual void onPopCull();
+
 private:
     class MCRec;
 
     SkClipStack fClipStack;
     SkDeque     fMCStack;
     // points to top of stack
     MCRec*      fMCRec;
     // the first N recs that can fit here mean we won't call malloc
     uint32_t    fMCRecStorage[32];
 
     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;
 
     SkSurface_Base*  fSurfaceBase;
     SkSurface_Base* getSurfaceBase() const { return fSurfaceBase; }
     void setSurfaceBase(SkSurface_Base* sb) {
         fSurfaceBase = sb;
     }
     friend class SkSurface_Base;
     friend class SkSurface_Gpu;
@@ skipping 122 matching lines @@
             fCanvas->endCommentGroup();
         }
     }
 
 private:
     SkCanvas* fCanvas;
 };
 #define SkAutoCommentBlock(...) SK_REQUIRE_LOCAL_VAR(SkAutoCommentBlock)
 
 #endif