Question

I have a bitmap flush with the bottom of my screen. When the user clicks a button I want it to rotate to the right by one degree. I am able to accomplish this but the problem is that the bottom of the item is no longer flush with the screen. I need it to appear to rotate on its bottom axis. I could use some hack to increment the x and y when its rotated (using trial and error I suppose) but is there a formula or something more elegant I can use?

public void rotate(int degrees)
    {
        Matrix mat = new Matrix();
        mat.postRotate(degrees);
        bitmap = Bitmap.createBitmap(bitmap, 0, 0, bitmap.getWidth(), bitmap.getHeight(), mat, true);       
    }

Answer 1

Could you not instead use the following method that Matrix also has:

postRotate (float degrees, float px, float py)

It enables rotation on the specified point.