Implement touch control

tools/viewer/Viewer.h

 /*
 * Copyright 2016 Google Inc.
 *
 * Use of this source code is governed by a BSD-style license that can be
 * found in the LICENSE file.
 */
 
 #ifndef Viewer_DEFINED
 #define Viewer_DEFINED
 
@@ skipping 15 matching lines @@
     void onIdle(double ms) override;
 
 private:
     void initSlides();
     void updateTitle();
     void setupCurrentSlide(int previousSlide);
 
     void drawStats(SkCanvas* canvas);
 
     void changeZoomLevel(float delta);
-    void updateMatrix();
+    SkMatrix computeMatrix();
 
     sk_app::Window*        fWindow;
 
     static const int kMeasurementCount = 64;  // should be power of 2 for fast mod
     double fMeasurements[kMeasurementCount];
     int fCurrentMeasurement;
 
     SkAnimTimer            fAnimTimer;
     SkTArray<sk_sp<Slide>> fSlides;
     int                    fCurrentSlide;
 
     bool                   fDisplayStats;
 
     // transform data
-    SkMatrix               fLocalMatrix;
     SkScalar               fZoomCenterX;
     SkScalar               fZoomCenterY;
     SkScalar               fZoomLevel;
     SkScalar               fZoomScale;
 
     sk_app::CommandSet     fCommands;
 };
 
 
 #endif