Android Multi touch zooming

Question

I am trying to implement multi touch zoom in and zoom out functionality to my application. My application is to view an slideshow of images. I tried to implement multi touch

Answer 1

Sure, you'll need to change this part:

else if (mode == ZOOM) {
      float newDist = spacing(event);
      Log.d(TAG, "newDist=" + newDist);
      if (newDist > 10f) {
         matrix.set(savedMatrix);
         float scale = newDist / oldDist;
         matrix.postScale(scale, scale, mid.x, mid.y);
      }
}

to

else if (mode == ZOOM) {
      float newDist = spacing(event);
      Log.d(TAG, "newDist=" + newDist);
      if (newDist > 10f) {
         matrix.set(savedMatrix);
         float scale = newDist / oldDist;

         // check scale is not too big or two small
         float newScale = scale*mCurrentScale;
         if (newScale > 10) {
             return false;
         } else if (newScale < 0.1) {
             return false;
         }
         mCurrentScale = newScale;

         matrix.postScale(scale, scale, mid.x, mid.y);
      }
}

and also add a variable mCurrentScale to your activity to remember to current scale like so:

public class Touch extends Activity implements OnTouchListener {
   // These matrices will be used to move and zoom image
   Matrix matrix = new Matrix();
   Matrix savedMatrix = new Matrix();

   // this is the new variable added
   float mCurrentScale = 1.0f;

...

Answer 2

This fixed the problem for me. After the image is zoomed in/out to the limit, it just stops going further. It's also smooth and there are no lags. 0.7 and 2.0 are the minimum and maximum zoom levels.

....
} else if (mode == ZOOM) {
    float[] f = new float[9];

    float newDist = spacing(event);
    if (newDist > 10f) {
            matrix.set(savedMatrix);
            float tScale = newDist / dist;
            matrix.postScale(tScale, tScale, mid.x, mid.y);
    }

    matrix.getValues(f);
    float scaleX = f[Matrix.MSCALE_X];
    float scaleY = f[Matrix.MSCALE_Y];

    if(scaleX <= 0.7f)
            matrix.postScale((0.7f)/scaleX, (0.7f)/scaleY, mid.x, mid.y);
    else if(scaleX >= 2.5f) 
            matrix.postScale((2.5f)/scaleX, (2.5f)/scaleY, mid.x, mid.y);

    }
....        

Answer 3

In my search and coding for the zooming imageview I came across a widget that is exactly copy of Gallery app zooming feature its easy to use. Although I have devised my own zoom Iamgeview but later I find its not agood thing to re- invent the wheel below is the link

Courtesy: Alessandro Crugnola

http://blog.sephiroth.it/2011/04/04/imageview-zoom-and-scroll/