matrix - 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

I hope the following sequence of code will help you:

Bitmap targetBitmap = Bitmap.createBitmap(targetWidth, targetHeight, config);
Canvas canvas = new Canvas(targetBitmap);
Matrix matrix = new Matrix();
matrix.setRotate(mRotation,source.getWidth()/2,source.getHeight()/2);
canvas.drawBitmap(source, matrix, new Paint());

If you check the following method from ~frameworksasegraphicsjavaandroidgraphicsBitmap.java

public static Bitmap createBitmap(Bitmap source, int x, int y, int width, int height,
        Matrix m, boolean filter)

this would explain what it does with rotation and translate.