Android: How to rotate a bitmap on a center point

Question

I've been looking for over a day for a solution to this problem but nothing helps, even the answers here. Documentation doesn't explain anything too.

I am simply trying to get a rotation in the direction of another object. The problem is that the bitmap is not rotated around a fixed point, but rather around the bitmaps (0,0).

Here is the code I am having troubles with:

  Matrix mtx = new Matrix();
  mtx.reset();
  mtx.preTranslate(-centerX, -centerY);
  mtx.setRotate((float)direction, -centerX, -centerY);
  mtx.postTranslate(pivotX, pivotY);
  Bitmap rotatedBMP = Bitmap.createBitmap(bitmap, 0, 0, spriteWidth, spriteHeight, mtx, true);
  this.bitmap = rotatedBMP;

The weird part is, it doesn't matter how I change the values within pre/postTranslate() and the float arguments in setRotation(). Can someone please help and push me in the right direction? :)

Answer 1

You can also rotate the ImageView using a RotateAnimation:

RotateAnimation rotateAnimation = new RotateAnimation(from, to,
Animation.RELATIVE_TO_SELF, 0.5f, Animation.RELATIVE_TO_SELF,
                0.5f);
rotateAnimation.setInterpolator(new LinearInterpolator());
rotateAnimation.setDuration(ANIMATION_DURATION);
rotateAnimation.setFillAfter(true);

imageView.startAnimation(rotateAnimation);

Answer 2

I came back to this problem now that we are finalizing the game and I just thought to post what worked for me.

This is the method for rotating the Matrix:

this.matrix.reset();
this.matrix.setTranslate(this.floatXpos, this.floatYpos);
this.matrix.postRotate((float)this.direction, this.getCenterX(), this.getCenterY()); 

(this.getCenterX() is basically the bitmaps X position + the bitmaps width / 2)

And the method for Drawing the bitmap (called via a RenderManager Class):

canvas.drawBitmap(this.bitmap, this.matrix, null);

So it is prettey straight forward but I find it abit strange that I couldn't get it to work by setRotate followed by postTranslate. Maybe some knows why this doesn't work? Now all the bitmaps rotate properly but it is not without some minor decrease in bitmap quality :/

Anyways, thanks for your help!