Add Sample slide for Rectanizers

src/gpu/GrRectanizer_pow2.h

 /*
 * Copyright 2014 Google Inc.
 *
 * Use of this source code is governed by a BSD-style license that can be
 * found in the LICENSE file.
 */
 
 #ifndef GrRectanizer_pow2_DEFINED
 #define GrRectanizer_pow2_DEFINED
 
 #include "GrRectanizer.h"
 
+// This Rectanizer quantizes the incoming rects to powers of 2. Each power
+// of two can have, at most, one active row/shelf. Once a row/shelf for
+// a particular power of two gets full its fRows entry is recycled to point
+// to a new row.
+// The skyline algorithm almost always provides a better packing.
 class GrRectanizerPow2 : public GrRectanizer {
 public:
     GrRectanizerPow2(int w, int h) : INHERITED(w, h) {
         this->reset();
     }
 
     virtual ~GrRectanizerPow2() { }
 
     virtual void reset() SK_OVERRIDE {
         fNextStripY = 0;
         fAreaSoFar = 0;
         sk_bzero(fRows, sizeof(fRows));
     }
 
     virtual bool addRect(int w, int h, GrIPoint16* loc) SK_OVERRIDE;
 
     virtual float percentFull() const SK_OVERRIDE {
         return fAreaSoFar / ((float)this->width() * this->height());
     }
 
 private:
     static const int kMIN_HEIGHT_POW2 = 2;
+    static const int kMaxExponent = 16;
 
     struct Row {
         GrIPoint16  fLoc;
+        // fRowHeight is actually known by this struct's position in fRows
+        // but it is used to signal if there exists an open row of this height
         int         fRowHeight;
 
         bool canAddWidth(int width, int containerWidth) const {
             return fLoc.fX + width <= containerWidth;
         }
     };
 
-    Row fRows[16];
+    Row fRows[kMaxExponent];    // 0-th entry will be unused
 
     int fNextStripY;
     int32_t fAreaSoFar;
 
     static int HeightToRowIndex(int height) {
         SkASSERT(height >= kMIN_HEIGHT_POW2);
-        return 32 - SkCLZ(height - 1);
+        int index = 32 - SkCLZ(height - 1);
+        SkASSERT(index < kMaxExponent);
+        return index;
     }
 
     bool canAddStrip(int height) const {
         return fNextStripY + height <= this->height();
     }
 
     void initRow(Row* row, int rowHeight) {
         row->fLoc.set(0, fNextStripY);
         row->fRowHeight = rowHeight;
         fNextStripY += rowHeight;
     }
 
     typedef GrRectanizer INHERITED;
 };
 
 #endif