Rotate canvas along its center based on user touch - Android

Question

I want to rotate the canvas circularly on its center axis based on user touch.

Like a old phone dialer .

i want to rotate based on center

but

Now its rotating based on top left corner .so i am able to see only 1/4 for rotation of image.

I have tried like as follows

onDraw(Canvas canvas){
  canvas.save();
  // do my rotation
  canvas.rotate(rotation,0,0);
  canvas.drawBitmap( ((BitmapDrawable)d).getBitmap(),0,0,p );
  canvas.restore();
}

@Override
        public boolean onTouchEvent(MotionEvent e) {
                  float x = e.getX();
              float y = e.getY();
              updateRotation(x,y);
              mPreviousX = x;
              mPreviousY = y;
            invalidate();
        }

  private void updateRotation(float x, float y) {

          double r = Math.atan2(x - centerX, centerY - y);
            rotation = (int) Math.toDegrees(r);
        }

i want to rotate based on center but its rotating based on top left corner .so i am able to see only 1/4 for rotation of image. — Ganapathy C, Aug 13 '11 at 10:42
Your question is answered here: http://stackoverflow.com/questions/4166917/android-how-to-rotate-a-bitmap-on-a-center-point — Ronnie, Aug 13 '11 at 11:52

score 2 · Answer 1 · answered Jan 08 '13 at 06:35

2

Instead of rotating the Canvas you can use x=0;

x=x+50;
yourview.setRotation(x);

use this on touch event and x=x-50 for rotating backword

I think it will help

answered Jan 08 '13 at 06:35

Bora

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score 2 · Accepted Answer · answered Aug 13 '11 at 12:00

2

You need to add this to your custom view methods

@Override     
public void onSizeChanged (int w, int h, int oldw, int oldh){ 
  super.onSizeChanged(w, h, oldw, oldh);         

  screenW = w;         
  screenH = h; 
}

This method will give you the canvas size then use

canvas.rotate(rotation, screenW / 2, screenH / 2);

answered Aug 13 '11 at 12:00

Lumis

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+1 for answer. Thanks dude this onSizeChanged method i left previously. now its working great. – Ganapathy C Aug 13 '11 at 13:16
1

great, if you need to rotate an image which is not in the center of the canvas, then just enter image's center as pivot rotate coordinates – Lumis Aug 13 '11 at 13:23

score 2 · Answer 3 · edited Nov 18 '12 at 18:31

2

Pass the point of rotation to rotate api:

canvas.rotate(rotation, 0, centerY);

edited Nov 18 '12 at 18:31

hasanghaforian

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answered Aug 13 '11 at 12:06

Ronnie

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thanks +1 for answer but canvas.rotate(rotation,0,centerY) gives me only half side (right half rotation) ,But canvas.rotate(rotation,centerX,centerY) gives me exact circular rotation on its midpoint. – Ganapathy C Aug 13 '11 at 13:19

Rotate canvas along its center based on user touch - Android

3 Answers3