Skip to content

Instantly share code, notes, and snippets.

@anorth
Created March 29, 2014 00:06
Show Gist options
  • Save anorth/9845602 to your computer and use it in GitHub Desktop.
Save anorth/9845602 to your computer and use it in GitHub Desktop.
Pinch-zoomable Android frame layout
package au.id.alexn;
import android.content.Context;
import android.util.AttributeSet;
import android.util.Log;
import android.view.MotionEvent;
import android.view.ScaleGestureDetector;
import android.view.View;
import android.widget.FrameLayout;
/**
* Layout that provides pinch-zooming of content. This view should have exactly one child
* view containing the content.
*/
public class ZoomLayout extends FrameLayout implements ScaleGestureDetector.OnScaleGestureListener {
private enum Mode {
NONE,
DRAG,
ZOOM
}
private static final String TAG = "ZoomLayout";
private static final float MIN_ZOOM = 1.0f;
private static final float MAX_ZOOM = 4.0f;
private Mode mode = Mode.NONE;
private float scale = 1.0f;
private float lastScaleFactor = 0f;
// Where the finger first touches the screen
private float startX = 0f;
private float startY = 0f;
// How much to translate the canvas
private float dx = 0f;
private float dy = 0f;
private float prevDx = 0f;
private float prevDy = 0f;
public ZoomLayout(Context context) {
super(context);
init(context);
}
public ZoomLayout(Context context, AttributeSet attrs) {
super(context, attrs);
init(context);
}
public ZoomLayout(Context context, AttributeSet attrs, int defStyle) {
super(context, attrs, defStyle);
init(context);
}
private void init(Context context) {
final ScaleGestureDetector scaleDetector = new ScaleGestureDetector(context, this);
this.setOnTouchListener(new View.OnTouchListener() {
@Override
public boolean onTouch(View view, MotionEvent motionEvent) {
switch (motionEvent.getAction() & MotionEvent.ACTION_MASK) {
case MotionEvent.ACTION_DOWN:
Log.i(TAG, "DOWN");
if (scale > MIN_ZOOM) {
mode = Mode.DRAG;
startX = motionEvent.getX() - prevDx;
startY = motionEvent.getY() - prevDy;
}
break;
case MotionEvent.ACTION_MOVE:
if (mode == Mode.DRAG) {
dx = motionEvent.getX() - startX;
dy = motionEvent.getY() - startY;
}
break;
case MotionEvent.ACTION_POINTER_DOWN:
mode = Mode.ZOOM;
break;
case MotionEvent.ACTION_POINTER_UP:
mode = Mode.DRAG;
break;
case MotionEvent.ACTION_UP:
Log.i(TAG, "UP");
mode = Mode.NONE;
prevDx = dx;
prevDy = dy;
break;
}
scaleDetector.onTouchEvent(motionEvent);
if ((mode == Mode.DRAG && scale >= MIN_ZOOM) || mode == Mode.ZOOM) {
getParent().requestDisallowInterceptTouchEvent(true);
float maxDx = (child().getWidth() - (child().getWidth() / scale)) / 2 * scale;
float maxDy = (child().getHeight() - (child().getHeight() / scale))/ 2 * scale;
dx = Math.min(Math.max(dx, -maxDx), maxDx);
dy = Math.min(Math.max(dy, -maxDy), maxDy);
Log.i(TAG, "Width: " + child().getWidth() + ", scale " + scale + ", dx " + dx
+ ", max " + maxDx);
applyScaleAndTranslation();
}
return true;
}
});
}
// ScaleGestureDetector
@Override
public boolean onScaleBegin(ScaleGestureDetector scaleDetector) {
Log.i(TAG, "onScaleBegin");
return true;
}
@Override
public boolean onScale(ScaleGestureDetector scaleDetector) {
float scaleFactor = scaleDetector.getScaleFactor();
Log.i(TAG, "onScale" + scaleFactor);
if (lastScaleFactor == 0 || (Math.signum(scaleFactor) == Math.signum(lastScaleFactor))) {
scale *= scaleFactor;
scale = Math.max(MIN_ZOOM, Math.min(scale, MAX_ZOOM));
lastScaleFactor = scaleFactor;
} else {
lastScaleFactor = 0;
}
return true;
}
@Override
public void onScaleEnd(ScaleGestureDetector scaleDetector) {
Log.i(TAG, "onScaleEnd");
}
private void applyScaleAndTranslation() {
child().setScaleX(scale);
child().setScaleY(scale);
child().setTranslationX(dx);
child().setTranslationY(dy);
}
private View child() {
return getChildAt(0);
}
}
@chensmic
Copy link

chensmic commented Feb 18, 2019

@Chirag117
In the ZoomLayout, change

FROM
case MotionEvent.ACTION_DOWN:
Log.i(TAG, "DOWN");
if (scale > MIN_ZOOM) {
mode = Mode.DRAG;
startX = motionEvent.getX() - prevDx;
startY = motionEvent.getY() - prevDy;
}
break;

TO

case MotionEvent.ACTION_DOWN:
Log.i(TAG, "DOWN");
if (scale > MIN_ZOOM) {
mode = Mode.DRAG;
startX = motionEvent.getX() - prevDx;
startY = motionEvent.getY() - prevDy;
}else{
//write your code here
}
break;

@totenhund
Copy link

To drag without having to zoom

You have to change

 case MotionEvent.ACTION_DOWN:
                        Log.i(TAG, "DOWN");
                        if (scale > MIN_ZOOM) {
                            Log.e("DOWN","Drag");
                            mode = Mode.DRAG;
                            startX = motionEvent.getX() - prevDx;
                            startY = motionEvent.getY() - prevDy;
                        }
                        break;

To

                        Log.i(TAG, "DOWN");
                        // TODO ORGINAL CODE UNCOMMENT BELOW CODE
                        /*if (scale > MIN_ZOOM) {*/
                            Log.e("DOWN","Drag");
                            mode = Mode.DRAG;
                            startX = motionEvent.getX() - prevDx;
                            startY = motionEvent.getY() - prevDy;
                        /*}*/
                        break;

And

                    getParent().requestDisallowInterceptTouchEvent(true);
                    float maxDx = (child().getWidth() - (child().getWidth() / scale)) / 2 * scale;
                    float maxDy = (child().getHeight() - (child().getHeight() / scale))/ 2 * scale;
                    dx = Math.min(Math.max(dx, -maxDx), maxDx);
                    dy = Math.min(Math.max(dy, -maxDy), maxDy);
                    Log.i(TAG, "Width: " + child().getWidth() + ", scale " + scale + ", dx " + dx
                            + ", max " + maxDx);
                    applyScaleAndTranslation();
                }

To

if ((mode == Mode.DRAG && scale >= MIN_ZOOM) || mode == Mode.ZOOM) {
                    getParent().requestDisallowInterceptTouchEvent(true);
                    float maxDx = (child().getWidth() - (child().getWidth() / scale)) / 2 * scale;
                    float maxDy = (child().getHeight() - (child().getHeight() / scale))/ 2 * scale;
                    /*dx = Math.min(Math.max(dx, -maxDx), maxDx);
                    dy = Math.min(Math.max(dy, -maxDy), maxDy);*/
                    Log.i(TAG, "Width: " + child().getWidth() + ", scale " + scale + ", dx " + dx
                            + ", max " + maxDx);
                    applyScaleAndTranslation();
                }

Full Code

public boolean onTouch(View view, MotionEvent motionEvent) {
                switch (motionEvent.getAction() & MotionEvent.ACTION_MASK) {
                    case MotionEvent.ACTION_DOWN:
                        Log.i(TAG, "DOWN");
                        // TODO ORGINAL CODE UNCOMMENT BELOW CODE
                        /*if (scale > MIN_ZOOM) {*/
                            Log.e("DOWN","Drag");
                            mode = Mode.DRAG;
                            startX = motionEvent.getX() - prevDx;
                            startY = motionEvent.getY() - prevDy;
                        /*}*/
                        break;
                    case MotionEvent.ACTION_MOVE:
                        if (mode == Mode.DRAG) {
                            Log.e("MOVE","Drag");
                            dx = motionEvent.getX() - startX;
                            dy = motionEvent.getY() - startY;
                        }
                        break;
                    case MotionEvent.ACTION_POINTER_DOWN:
                        mode = Mode.ZOOM;
                        break;
                    // TODO ORGINAL CODE UNCOMMENT BELOW CODE
                    /*case MotionEvent.ACTION_POINTER_UP:mode = Mode.DRAG;*/
                    case MotionEvent.ACTION_POINTER_UP: mode = Mode.NONE;
                        Log.e("ACTION_POINTER_UP","Drag");
                        break;

                    case MotionEvent.ACTION_UP:
                        Log.i(TAG, "UP");
                        Log.e("ACTION_UP","None");
                        mode = Mode.NONE;
                        prevDx = dx;
                        prevDy = dy;
                        break;
                }
                scaleDetector.onTouchEvent(motionEvent);

                if ((mode == Mode.DRAG && scale >= MIN_ZOOM) || mode == Mode.ZOOM) {
                    getParent().requestDisallowInterceptTouchEvent(true);
                    float maxDx = (child().getWidth() - (child().getWidth() / scale)) / 2 * scale;
                    float maxDy = (child().getHeight() - (child().getHeight() / scale))/ 2 * scale;
                    // TODO ORGINAL CODE UNCOMMENT BELOW CODE
                    /*dx = Math.min(Math.max(dx, -maxDx), maxDx);
                    dy = Math.min(Math.max(dy, -maxDy), maxDy);*/
                    Log.i(TAG, "Width: " + child().getWidth() + ", scale " + scale + ", dx " + dx
                            + ", max " + maxDx);
                    applyScaleAndTranslation();
                }

                return true;
            }

How to set boundaries for drag?

@vempatissn
Copy link

Pan is compulsorily required when we zoom. Both functions are provided in a single class. Great tutorial. Thank you anorth for the post.

@wangtsung
Copy link

not working below android 7.0

@shivammonga
Copy link

zooming and panning is not working with mouse. how can i do that?

@jacklai24
Copy link

I am facing a problem if the zoom layout includes a landscape image. It will leave space at the top and bottom. When I zoom and drag the image. It will be outside the top or bottom boundary. How to calculate the correct "maxDy" in this case?

@AlexEkaterinin
Copy link

It works perfectly, thank you very much!

@chensmic
Copy link

chensmic commented Oct 2, 2023 via email

@hanzlasheikh
Copy link

How can we reset the zoom?

@Nishchay2211
Copy link

Hi how can we achieve the focus zoom in this code? I mean when ever we zoom the image it always zoom from center. If we want to zoom and see a specific part of image it doesn't work. I try making use of "getFocusX() & getFocusY()" but it is still not zooming on the focused position but always to centre.

Sign up for free to join this conversation on GitHub. Already have an account? Sign in to comment