Android Scaling Zoom Bitmap on Canvas

Question

I need to add the following functions in my application

I need to display bitmap in canvas

Then the user can enlarge and reduce the raster image in Canvas

How to do it? I only need this in Canvas and not in ImageView

All the answers are not very helpful to me .. so I think I’ll update my question

Basically, I need a simple button 2 and a canvas ...

when you press the button for the first time, the image on the canvas can rotate / scale and scale, and when you press the second button, it should display the enlarged or reduced image that was created by the user, and after that the user should not be able to scale or scale that canvas

Answer 1

If you are enlarging and reducing the raster image in the canvas, use the code below, which

Add your code to your activity

MyView myView = new MyView(this); setContentView(myView); 

and below your view.

 public class MyView extends View { private Drawable image; private ScaleGestureDetector scaleDetector; private float scaleFactor = 1.f; public MyView(Context context) { super(context); init(context); } public MyView(Context context, AttributeSet attrs) { super(context, attrs); init(context); } public MyView(Context context, AttributeSet attrs, int defStyle) { super(context, attrs, defStyle); init(context); } private void init(Context ctx) { image = getResources().getDrawable(R.drawable.ic_launcher); image.setBounds(0, 0, image.getIntrinsicWidth(), image.getIntrinsicHeight()); scaleDetector = new ScaleGestureDetector(ctx, new ScaleListener()); } @Override protected void onDraw(Canvas canvas) { canvas.save(); canvas.scale(scaleFactor, scaleFactor); image.draw(canvas); canvas.restore(); }; @Override public boolean onTouchEvent(MotionEvent ev) { scaleDetector.onTouchEvent(ev); return true; } private class ScaleListener extends ScaleGestureDetector.SimpleOnScaleGestureListener { @Override public boolean onScale(ScaleGestureDetector detector) { scaleFactor *= detector.getScaleFactor(); scaleFactor = Math.max(0.1f, Math.min(scaleFactor, 10.0f)); invalidate(); return true; } } } 

Answer 2

You can use this custom view class, it provides drag and drop along with the zoom effect. I am not the original author of this class, I copied it from this tutorial . You can go through the manual pages if you like to see step by step how to achieve this effect.

 public class ZoomView extends View { //These two constants specify the minimum and maximum zoom private static float MIN_ZOOM = 1f; private static float MAX_ZOOM = 5f; private float scaleFactor = 1.f; private ScaleGestureDetector detector; //These constants specify the mode that we're in private static int NONE = 0; private static int DRAG = 1; private static int ZOOM = 2; private int mode; //These two variables keep track of the X and Y coordinate of the finger when it first //touches the screen private float startX = 0f; private float startY = 0f; //These two variables keep track of the amount we need to translate the canvas along the X //and the Y coordinate private float translateX = 0f; private float translateY = 0f; //These two variables keep track of the amount we translated the X and Y coordinates, the last time we //panned. private float previousTranslateX = 0f; private float previousTranslateY = 0f; public ZoomView(Context context) { super(context); detector = new ScaleGestureDetector(getContext(), new ScaleListener()); } @Override public boolean onTouchEvent(MotionEvent event) { switch (event.getAction() & MotionEvent.ACTION_MASK) { case MotionEvent.ACTION_DOWN: mode = DRAG; //We assign the current X and Y coordinate of the finger to startX and startY minus the previously translated //amount for each coordinates This works even when we are translating the first time because the initial //values for these two variables is zero. startX = event.getX() - previousTranslateX; startY = event.getY() - previousTranslateY; break; case MotionEvent.ACTION_MOVE: translateX = event.getX() - startX; translateY = event.getY() - startY; //We cannot use startX and startY directly because we have adjusted their values using the previous translation values. //This is why we need to add those values to startX and startY so that we can get the actual coordinates of the finger. double distance = Math.sqrt(Math.pow(event.getX() - (startX + previousTranslateX), 2) + Math.pow(event.getY() - (startY + previousTranslateY), 2) ); if(distance > 0) { dragged = true; } break; case MotionEvent.ACTION_POINTER_DOWN: mode = ZOOM; break; case MotionEvent.ACTION_UP: mode = NONE; dragged = false; //All fingers went up, so let save the value of translateX and translateY into previousTranslateX and //previousTranslate previousTranslateX = translateX; previousTranslateY = translateY; break; case MotionEvent.ACTION_POINTER_UP: mode = DRAG; //This is not strictly necessary; we save the value of translateX and translateY into previousTranslateX //and previousTranslateY when the second finger goes up previousTranslateX = translateX; previousTranslateY = translateY; break; } detector.onTouchEvent(event); //We redraw the canvas only in the following cases: // // o The mode is ZOOM // OR // o The mode is DRAG and the scale factor is not equal to 1 (meaning we have zoomed) and dragged is // set to true (meaning the finger has actually moved) if ((mode == DRAG && scaleFactor != 1f && dragged) || mode == ZOOM) { invalidate(); } return true; } @Override public void onDraw(Canvas canvas) { super.onDraw(canvas); canvas.save(); //We're going to scale the X and Y coordinates by the same amount canvas.scale(scaleFactor, scaleFactor); //If translateX times -1 is lesser than zero, let set it to zero. This takes care of the left bound if((translateX * -1) < 0) { translateX = 0; } //This is where we take care of the right bound. We compare translateX times -1 to (scaleFactor - 1) * displayWidth. //If translateX is greater than that value, then we know that we've gone over the bound. So we set the value of //translateX to (1 - scaleFactor) times the display width. Notice that the terms are interchanged; it the same //as doing -1 * (scaleFactor - 1) * displayWidth else if((translateX * -1) > (scaleFactor - 1) * displayWidth) { translateX = (1 - scaleFactor) * displayWidth; } if(translateY * -1 < 0) { translateY = 0; } //We do the exact same thing for the bottom bound, except in this case we use the height of the display else if((translateY * -1) > (scaleFactor - 1) * displayHeight) { translateY = (1 - scaleFactor) * displayHeight; } //We need to divide by the scale factor here, otherwise we end up with excessive panning based on our zoom level //because the translation amount also gets scaled according to how much we've zoomed into the canvas. canvas.translate(translateX / scaleFactor, translateY / scaleFactor); /* The rest of your canvas-drawing code */ canvas.restore(); } private class ScaleListener extends ScaleGestureDetector.SimpleOnScaleGestureListener { @Override public boolean onScale(ScaleGestureDetector detector) { scaleFactor *= detector.getScaleFactor(); scaleFactor = Math.max(MIN_ZOOM, Math.min(scaleFactor, MAX_ZOOM)); return true; } } }