Add the machinery to GrDrawTarget to enable topological sorting

src/gpu/GrDrawTarget.h

Index: src/gpu/GrDrawTarget.h
diff --git a/src/gpu/GrDrawTarget.h b/src/gpu/GrDrawTarget.h
index db637d52b10add9e59421d726cb1bab2d44710a5..112357d1f92d165195dad77b3aaa9c2136447ec6 100644
--- a/src/gpu/GrDrawTarget.h
+++ b/src/gpu/GrDrawTarget.h
@@ -49,14 +49,48 @@ public:
 
     ~GrDrawTarget() override;
 
+    enum Flags {
+        kClosed_Flag    = 0x01,   //!< This drawTarget can't accept any more batches
+
+        kWasOutput_Flag = 0x02,   //!< Flag for topological sorting
+        kTempMark_Flag  = 0x04,   //!< Flag for topological sorting
+    };
+
     void makeClosed() {
         // We only close drawTargets When MDB is enabled. When MDB is disabled there is only
         // ever one drawTarget and all calls will be funnelled into it.
 #ifdef ENABLE_MDB
-        fClosed = true;
+        this->setFlag(kClosed_Flag);
 #endif
     }
-    bool isClosed() const { return fClosed; }
+    bool isClosed() const { return this->isSetFlag(kClosed_Flag); }
+
+    void setFlag(uint32_t flag) {

[bsalomon, 2015/10/20 13:57:19]

I'm wondering if all this stuff needs to be public? If TopoTraits was friended
or nested here could this all be private?

[robertphillips, 2015/10/20 14:10:49]

Done.

+        fFlags |= flag;
+    }
+
+    void resetFlag(uint32_t flag) {
+        fFlags &= ~flag;
+    }
+
+    bool isSetFlag(uint32_t flag) const {
+        return SkToBool(fFlags & flag);
+    }
+
+    // This drawTarget relies on the contents of 'dependedOn'
+    void addDependency(GrSurface* dependedOn);
+
+    bool dependsOn(GrDrawTarget* dependedOn) const {
+        return fDependencies.find(dependedOn) >= 0;
+    }
+
+    int numDependencies() const {
+        return fDependencies.count();
+    }
+
+    GrDrawTarget* dependency(int index) {
+        return fDependencies[index];
+    }
 
     /**
      * Empties the draw buffer of any queued up draws.
@@ -231,6 +265,8 @@ private:
                            GrScissorState*,
                            const SkRect* devBounds);
 
+    void addDependency(GrDrawTarget* dependedOn);
+
     // Used only by CMM.
     void clearStencilClip(const SkIRect&, bool insideClip, GrRenderTarget*);
 
@@ -244,7 +280,10 @@ private:
     bool                                        fFlushing;
     int                                         fFirstUnpreparedBatch;
 
-    bool                                        fClosed;
+    uint32_t                                    fFlags;
+
+    // 'this' drawTarget relies on the output of the drawTargets in 'fDependencies'
+    SkTDArray<GrDrawTarget*>                    fDependencies;
 
     typedef SkRefCnt INHERITED;
 };