pdfviewer: more code comments + concat the pdf matrix with the existing matrix in canvas, instead o…

experimental/PdfViewer/SkTrackDevice.h

 /*
  * Copyright 2013 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #ifndef SkTrackDevice_DEFINED
 #define SkTrackDevice_DEFINED
 
 #include "SkBitmapDevice.h"
 #include "SkTracker.h"
 
 /** \class SkTrackDevice
  *
  *   A Track Device is used to track that callstack of an operation that affected some pixels.
  *   It can be used with SampleApp to investigate bugs (CL not checked in yet).
  *
+ *   every drawFoo is implemented as such:
+ *      before();   // - collects state of interesting pixels
+ *      INHERITED::drawFoo(...);
+ *      after();  // - checks if pixels of interest, and issue a breakpoint.
+ *
  */
 class SkTrackDevice : public SkBitmapDevice {
 public:
     SK_DECLARE_INST_COUNT(SkTrackDevice)
 
     SkTrackDevice(const SkBitmap& bitmap) : SkBitmapDevice(bitmap)
                                           , fTracker(NULL) {}
 
     SkTrackDevice(const SkBitmap& bitmap, const SkDeviceProperties& deviceProperties)
         : SkBitmapDevice(bitmap, deviceProperties)
         , fTracker(NULL) {}
 
     SkTrackDevice(SkBitmap::Config config, int width, int height, bool isOpaque = false)
         : SkBitmapDevice(config, width, height, isOpaque)
         , fTracker(NULL) {}
 
     SkTrackDevice(SkBitmap::Config config, int width, int height, bool isOpaque,
                   const SkDeviceProperties& deviceProperties)
         : SkBitmapDevice(config, width, height, isOpaque, deviceProperties)
         , fTracker(NULL) {}
 
     virtual ~SkTrackDevice() {}
 
+    // Install a tracker - we can reuse the tracker between multiple devices, and the state of the
+    // tracker is preserved - number and location of poinbts, ...
     void installTracker(SkTracker* tracker) {
         fTracker = tracker;
         fTracker->newFrame();
     }
 
 protected:
     virtual void clear(SkColor color) {
         before();
         INHERITED::clear(color);
         after();
@@ skipping 130 matching lines @@
         }
     }
 
 private:
     SkTracker* fTracker;
 
     typedef SkBitmapDevice INHERITED;
 };
 
 #endif  // SkTrackDevice_DEFINED