Added documentation of stage/TU allocation

http://codereview.appspot.com/6199058/



git-svn-id: http://skia.googlecode.com/svn/trunk@3888 2bbb7eff-a529-9590-31e7-b0007b416f81

include/gpu/GrTextContext.h

@@ -22,6 +22,11 @@ class GrPaint;
 class SkGpuDevice;
 class SkPaint;
 
+/**
+ * Derived classes can use stages GrPaint::kTotalStages through 
+ * GrDrawState::kNumStages-1. The stages before GrPaint::kTotalStages
+ * are reserved for setting up the draw (i.e., textures and filter masks).
+ */
 class GrTextContext: public GrRefCnt {
 protected:
     GrContext*      fContext;

src/gpu/GrDrawState.h

@@ -36,6 +36,11 @@ public:
      * the last enabled stage. The presence or absence of texture coordinates
      * for each stage in the vertex layout indicates whether a stage is enabled
      * or not.
+     *
+     * Stages 0 through GrPaint::kTotalStages-1 are reserved for setting up
+     * the draw (i.e., textures and filter masks). Stages GrPaint::kTotalStages 
+     * through kNumStages-1 are earmarked for use by GrTextContext and 
+     * GrPathRenderer-derived classes.
      */
     enum {
         kNumStages = 4,

src/gpu/GrPathRenderer.h

@@ -21,6 +21,10 @@ struct GrPoint;
 
 /**
  *  Base class for drawing paths into a GrDrawTarget.
+ *
+ *  Derived classes can use stages GrPaint::kTotalStages through 
+ *  GrDrawState::kNumStages-1. The stages before GrPaint::kTotalStages
+ *  are reserved for setting up the draw (i.e., textures and filter masks).
  */
 class GR_API GrPathRenderer : public GrRefCnt {
 public: