Pinching Zoom in android Image View or Bitmap

This is little bit complex article. In android , we can achieve pinch zoom with two or more than two finger. But it s little bit complex. I have developed it with the help of one GuitHub project.

Here we use Bitmap, Gesture, Matrix and other Bitmap Basic function. I have develop simply three classes.
main class is TouchImageView.java that is a Image-View.you can set this class Object anywhere

Make one project and use my classes

main class TouchImageView.java 




package com.ahmad;

import android.content.Context;
import android.graphics.Bitmap;
import android.graphics.Matrix;
import android.graphics.PointF;
import android.util.FloatMath;
import android.util.Log;
import android.view.MotionEvent;
import android.view.View;
import android.widget.ImageView;

public class TouchImageView extends ImageView {

    private static final String TAG = "Touch";
    Matrix matrix = new Matrix();
    Matrix savedMatrix = new Matrix();

    // We can be in one of these 3 states
    static final int NONE = 0;
    static final int DRAG = 1;
    static final int ZOOM = 2;
    int mode = NONE;

    // Remember some things for zooming
    PointF start = new PointF();
    PointF mid = new PointF();
    float oldDist = 1f;

    Context context;
 
    public TouchImageView(Context context) {
        super(context);
        super.setClickable(true);
        this.context = context;

        matrix.setTranslate(1f, 1f);
        setImageMatrix(matrix);
        setScaleType(ScaleType.MATRIX);

        setOnTouchListener(new OnTouchListener() {

            @Override
            public boolean onTouch(View v, MotionEvent rawEvent) {
                WrapMotionEvent event = WrapMotionEvent.wrap(rawEvent);

                // Dump touch event to log
//                if (Viewer.isDebug == true){
//                    dumpEvent(event);
//                }

                // Handle touch events here...
                switch (event.getAction() & MotionEvent.ACTION_MASK) {
                case MotionEvent.ACTION_DOWN:
                    savedMatrix.set(matrix);
                    start.set(event.getX(), event.getY());
                    Log.d(TAG, "mode=DRAG");
                    mode = DRAG;
                    break;
                case MotionEvent.ACTION_POINTER_DOWN:
                    oldDist = spacing(event);
                    Log.d(TAG, "oldDist=" + oldDist);
                    if (oldDist > 10f) {
                        savedMatrix.set(matrix);
                        midPoint(mid, event);
                        mode = ZOOM;
                        Log.d(TAG, "mode=ZOOM");
                    }
                    break;
                case MotionEvent.ACTION_UP:
                    int xDiff = (int) Math.abs(event.getX() - start.x);
                    int yDiff = (int) Math.abs(event.getY() - start.y);
                    if (xDiff < 8 && yDiff < 8){
                        performClick();
                    }
                case MotionEvent.ACTION_POINTER_UP:
                    mode = NONE;
                    Log.d(TAG, "mode=NONE");
                    break;
                case MotionEvent.ACTION_MOVE:
                    if (mode == DRAG) {
                        // ...
                        matrix.set(savedMatrix);
                        matrix.postTranslate(event.getX() - start.x, event.getY() - start.y);
                    } 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);
                        }
                    }
                    break;
                }
                setImageMatrix(matrix);
                return true; // indicate event was handled
            }

        });
    }
    public void setImage(Bitmap bm, int displayWidth, int displayHeight) {
        super.setImageBitmap(bm);

        //Fit to screen.
        float scale;
        if ((displayHeight / bm.getHeight()) >= (displayWidth / bm.getWidth())){
            scale =  (float)displayWidth / (float)bm.getWidth();
        } else {
            scale = (float)displayHeight / (float)bm.getHeight();
        }

        savedMatrix.set(matrix);
        matrix.set(savedMatrix);
        matrix.postScale(scale, scale, mid.x, mid.y);
        setImageMatrix(matrix);
        // Center the image
        float redundantYSpace = (float)displayHeight - (scale * (float)bm.getHeight()) ;
        float redundantXSpace = (float)displayWidth - (scale * (float)bm.getWidth());
        redundantYSpace /= (float)2;
        redundantXSpace /= (float)2;
        savedMatrix.set(matrix);
        matrix.set(savedMatrix);
        matrix.postTranslate(redundantXSpace, redundantYSpace);
        setImageMatrix(matrix);
    }
    /** Show an event in the LogCat view, for debugging */
@SuppressWarnings("unused")
private void dumpEvent(WrapMotionEvent event) {
        String names[] = { "DOWN", "UP", "MOVE", "CANCEL", "OUTSIDE",
            "POINTER_DOWN", "POINTER_UP", "7?", "8?", "9?" };
        StringBuilder sb = new StringBuilder();
        int action = event.getAction();
        int actionCode = action & MotionEvent.ACTION_MASK;
        sb.append("event ACTION_").append(names[actionCode]);
        if (actionCode == MotionEvent.ACTION_POINTER_DOWN
                || actionCode == MotionEvent.ACTION_POINTER_UP) {
            sb.append("(pid ").append(
                    action >> MotionEvent.ACTION_POINTER_ID_SHIFT);
            sb.append(")");
        }
        sb.append("[");
        for (int i = 0; i < event.getPointerCount(); i++) {
            sb.append("#").append(i);
            sb.append("(pid ").append(event.getPointerId(i));
            sb.append(")=").append((int) event.getX(i));
            sb.append(",").append((int) event.getY(i));
            if (i + 1 < event.getPointerCount())
            sb.append(";");
        }
        sb.append("]");
        Log.d(TAG, sb.toString());
    }
    /** Determine the space between the first two fingers */
    private float spacing(WrapMotionEvent event) {
        float x = event.getX(0) - event.getX(1);
        float y = event.getY(0) - event.getY(1);
        return FloatMath.sqrt(x * x + y * y);
    }
    /** Calculate the mid point of the first two fingers */
    private void midPoint(PointF point, WrapMotionEvent event) {
        float x = event.getX(0) + event.getX(1);
        float y = event.getY(0) + event.getY(1);
        point.set(x / 2, y / 2);
    }
}

Motion class to help in touch event
package com.ahmad;

import android.view.MotionEvent;
public class EclairMotionEvent extends WrapMotionEvent {
    protected EclairMotionEvent(MotionEvent event) {
            super(event);
    }
    public float getX(int pointerIndex) {
            return event.getX(pointerIndex);
    }
    public float getY(int pointerIndex) {
            return event.getY(pointerIndex);
    }
    public int getPointerCount() {
            return event.getPointerCount();
    }
    public int getPointerId(int pointerIndex) {
            return event.getPointerId(pointerIndex);
    }
}

Class to keep information about Pointer ID

package com.ahmad;

import android.view.MotionEvent;

public class WrapMotionEvent {

protected MotionEvent event;

protected WrapMotionEvent(MotionEvent event) {

this.event = event;

}

      static public WrapMotionEvent wrap(MotionEvent event) {

try {

return new EclairMotionEvent(event);

} catch (VerifyError e) {

return new WrapMotionEvent(event);

}

}

public int getAction() {

return event.getAction();

}

public float getX() {

return event.getX();

}

public float getX(int pointerIndex) {

verifyPointerIndex(pointerIndex);

return getX();

}

public float getY() {

return event.getY();

}

public float getY(int pointerIndex) {

verifyPointerIndex(pointerIndex);

return getY();

}

public int getPointerCount() {

return 1;

}

public int getPointerId(int pointerIndex) {

verifyPointerIndex(pointerIndex);

return 0;

}

private void verifyPointerIndex(int pointerIndex) {

if (pointerIndex > 0) {

throw new IllegalArgumentException(

"Invalid pointer index for Donut/Cupcake");

}

}

}

Notable thing is that this pinch zoom will only work above Android 2.0. Lower version does not support multiple finger