Do not calculate many sierpinski fractals for each nanobench run unless needed

bench/PictureNestingBench.cpp

 /*
  * Copyright 2014 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #include "Benchmark.h"
 #include "SkCanvas.h"
 #include "SkColor.h"
 #include "SkNullCanvas.h"
 #include "SkPaint.h"
 #include "SkPicture.h"
 #include "SkPictureRecorder.h"
 #include "SkString.h"
 
+#include <math.h>
+
 class PictureNesting : public Benchmark {
 public:
     PictureNesting(const char* name, int maxLevel, int maxPictureLevel)
         : fMaxLevel(maxLevel)
         , fMaxPictureLevel(maxPictureLevel) {
-
+        fName.printf("picture_nesting_%s_%d", name, this->countPics());
         fPaint.setColor(SK_ColorRED);
         fPaint.setAntiAlias(true);
         fPaint.setStyle(SkPaint::kStroke_Style);
-        SkAutoTUnref<SkCanvas> nullCanvas(SkCreateNullCanvas());
-        fName.printf("picture_nesting_%s_%d", name, this->sierpinsky(nullCanvas, 0, fPaint));
     }
 
 protected:
     virtual const char* onGetName() SK_OVERRIDE {
         return fName.c_str();
     }
 
     void doDraw(SkCanvas* canvas) {
         SkIPoint canvasSize = onGetSize();
         canvas->save();
         canvas->scale(SkIntToScalar(canvasSize.x()), SkIntToScalar(canvasSize.y()));
 
-        this->sierpinsky(canvas, 0, fPaint);
+        SkDEBUGCODE(int pics = ) this->sierpinsky(canvas, 0, fPaint);
+        SkASSERT(pics == this->countPics());
 
         canvas->restore();
     }
 
     int sierpinsky(SkCanvas* canvas, int lvl, const SkPaint& paint) {
         if (++lvl > fMaxLevel) {
             return 0;
         }
 
         int pics = 0;
@@ skipping 28 matching lines @@
             canvas->drawPicture(picture);
         }
 
         return pics;
     }
 
     int fMaxLevel;
     int fMaxPictureLevel;
 
 private:
+    int countPics() const {
+        // Solve: pics from sierpinsky
+        // f(m) = 1 + 3*f(m - 1)
+        // f(0) = 0
+        //   via "recursive function to closed form" tricks
+        // f(m) = 1/2 (3^m - 1)
+        return static_cast<int>((pow(3.0, fMaxPictureLevel) - 1.0) / 2.0);
+    }
+
     SkString fName;
     SkPaint  fPaint;
 
     typedef Benchmark INHERITED;
 };
 
 class PictureNestingRecording : public PictureNesting {
 public:
     PictureNestingRecording(int maxLevel, int maxPictureLevel)
         : INHERITED("recording", maxLevel, maxPictureLevel) {
@@ skipping 17 matching lines @@
     }
 
 private:
     typedef PictureNesting INHERITED;
 };
 
 class PictureNestingPlayback : public PictureNesting {
 public:
     PictureNestingPlayback(int maxLevel, int maxPictureLevel)
         : INHERITED("playback", maxLevel, maxPictureLevel) {
+    }
+protected:
+    virtual void onPreDraw() SK_OVERRIDE {
+        this->INHERITED::onPreDraw();
 
         SkIPoint canvasSize = onGetSize();
         SkPictureRecorder recorder;
         SkCanvas* c = recorder.beginRecording(SkIntToScalar(canvasSize.x()),
                                               SkIntToScalar(canvasSize.y()));
 
         this->doDraw(c);
         fPicture.reset(recorder.endRecording());
     }
 
-protected:
     virtual void onDraw(const int loops, SkCanvas* canvas) {
         for (int i = 0; i < loops; i++) {
             canvas->drawPicture(fPicture);
         }
     }
 
 private:
     SkAutoTUnref<SkPicture> fPicture;
 
     typedef PictureNesting INHERITED;
@@ skipping 11 matching lines @@
 
 DEF_BENCH( return new PictureNestingPlayback(8, 0); )
 DEF_BENCH( return new PictureNestingPlayback(8, 1); )
 DEF_BENCH( return new PictureNestingPlayback(8, 2); )
 DEF_BENCH( return new PictureNestingPlayback(8, 3); )
 DEF_BENCH( return new PictureNestingPlayback(8, 4); )
 DEF_BENCH( return new PictureNestingPlayback(8, 5); )
 DEF_BENCH( return new PictureNestingPlayback(8, 6); )
 DEF_BENCH( return new PictureNestingPlayback(8, 7); )
 DEF_BENCH( return new PictureNestingPlayback(8, 8); )