java - Android Canvas - Scale and Translate -

i have svg want zoom , pan using gestures in android. works, not smoothly enough tastes. how can improve class have smooth panning works @ zoom levels , stays under finger, scales using pinch gesture zooms area of gesture (aka focus) , bonus double tapping should result in snapping image 1.0? i'm using svg library. acceptable answer should meet these functional requirements, not jump around unexpectedly , stick gesturedetectors unless case can made won't work.

public class mapview extends viewgroup {     private static final float minimum_scale_factor = 1.0f;     private static final float maximum_scale_factor = 10.0f;      private picture mpicture;     private paint mpaint;      private scalegesturedetector mscaledetector;     private gesturedetector mmovedetector;      private float mscalefactor;     private float mscalefocusx;     private float mscalefocusy;     private float mfocusx = 0.0f;     private float mfocusy = 0.0f;      private float mimageheight;     private float mimagewidth;     private int mviewheight;     private int mviewwidth;     private rectf mdrawingrect;       public mapview(context context) {         super(context);          init(context);     }      public mapview(context context, attributeset attrs) {         super(context, attrs);          init(context);      }      public mapview(context context, attributeset attrs, int defstyle) {         super(context, attrs, defstyle);          init(context);     }      public void init(context context) {         log.d(getclass().getcanonicalname(), "initialized.");          this.setbackgroundcolor(color.white);          this.mpaint = new paint();         mpaint.setstyle(paint.style.stroke);         mpaint.setcolor(color.blue);         mpaint.setstrokewidth(2);         mpaint.setantialias(true);          this.mscalefactor = minimum_scale_factor;          // setup gesture detectors         this.mscaledetector = new scalegesturedetector(context, new scalelistener());         this.mmovedetector = new gesturedetector(context, new movelistener());     }      @override     protected void onlayout(boolean changed, int l, int t, int r, int b) {         log.d(getclass().getcanonicalname(), "onlayout");          this.mdrawingrect = getdrawingsquare();     }      @override     protected void onsizechanged(int w, int h, int oldw, int oldh) {         super.onsizechanged(w, h, oldw, oldh);          this.mviewwidth = w;         this.mviewheight = h;     }      @override     protected void ondraw(canvas canvas) {         super.ondraw(canvas);          log.d(getclass().getcanonicalname(), "ondraw()");          canvas.save();         canvas.scale(mscalefactor, mscalefactor, mscalefocusx, mscalefocusy);          canvas.translate(mfocusx, mfocusy);          canvas.drawrect((int) mdrawingrect.left, (int) mdrawingrect.top, (int) mdrawingrect.right, (int) mdrawingrect.bottom, mpaint);         canvas.drawpicture(mpicture, mdrawingrect);          canvas.restore();     }      @override     public boolean ontouchevent(motionevent ev) {         mscaledetector.ontouchevent(ev);         mmovedetector.ontouchevent(ev);          return true;     }      public rectf getdrawingsquare() {         float width = getwidth();         float height = getheight();         log.d(getclass().getcanonicalname(), "picture width " + width + " - height " + height);          float side = math.min(width, height);          return new rectf(0, 0, side, side);     }      public void setsvg(svg svg) {         log.d(getclass().getcanonicalname(), "svg picture.");          this.mpicture = svg.getpicture();         this.mimageheight = mpicture.getheight();         this.mimagewidth = mpicture.getwidth();          invalidate();     }      private class scalelistener extends scalegesturedetector.simpleonscalegesturelistener {         @override         public boolean onscale(scalegesturedetector detector) {             mscalefactor *= detector.getscalefactor(); // scale change since previous event             mscalefocusx = detector.getfocusx();             mscalefocusy = detector.getfocusy();              // don't let object small or large.             mscalefactor = math.max(minimum_scale_factor, math.min(mscalefactor, maximum_scale_factor));              invalidate();              return true;         }     }      private class movelistener extends gesturedetector.simpleongesturelistener { //        @override //        public boolean ondown(motionevent e) { //            return true; //        }          @override         public boolean onscroll(motionevent e1, motionevent e2, float distancex, float distancey) {             scrollby((int)distancex, (int)distancey); //            mfocusx += distancex; //            mfocusy += distancey; //            return true;             return true;         }     } } 

if (re)drawing picture isn't fast enough, might have draw bitmap instead , scroll about.