Correct gesture scale and translation

include/views/SkTouchGesture.h

 
 /*
  * Copyright 2011 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 #ifndef SkTouchGesture_DEFINED
 #define SkTouchGesture_DEFINED
 
@@ skipping 25 matching lines @@
     void touchMoved(void* owner, float x, float y);
     void touchEnd(void* owner);
     void reset();
 
     bool isActive() { return fFlinger.isActive(); }
     void stop() { fFlinger.stop(); }
 
     const SkMatrix& localM();
     const SkMatrix& globalM() const { return fGlobalM; }
 
+    void setTransLimit(const SkRect& contentRect, const SkRect& windowRect);
+
 private:
     enum State {
         kEmpty_State,
         kTranslate_State,
         kZoom_State,
     };
 
     struct Rec {
         void*   fOwner;
         float   fStartX, fStartY;
         float   fPrevX, fPrevY;
         float   fLastX, fLastY;
         float   fPrevT, fLastT;
     };
     SkTDArray<Rec> fTouches;
 
     State           fState;
     SkMatrix        fLocalM, fGlobalM;
     SkFlingState    fFlinger;
     double          fLastUpMillis;
     SkPoint         fLastUpP;
 
+    // The following rects are used to limit the translation so the content never leaves the window
+    SkRect          fContentRect, fWindowRect;
+    bool            fIsTransLimited = false;
 
+    void limitTrans(); // here we only limit the translation with respect to globalM
     void flushLocalM();
     int findRec(void* owner) const;
     void appendNewRec(void* owner, float x, float y);
     float computePinch(const Rec&, const Rec&);
     float limitTotalZoom(float scale) const;
     bool handleDblTap(float, float);
 };
 
 #endif