代码使用矩阵旋转位图导致强制关闭

Question

I m working on a simple game where a ball tumbles on a slope and has to avoid the obstacles by jumping. The problem comes when I am trying to rotate the ball object using the Matrix . I am using the following code:-

private void rotateMe() {
    if(jump==0){
        Matrix mtx=new Matrix();
        mtx.postRotate(deg);
        Bitmap rotatedBMP=Bitmap.createBitmap(bm, 0, 0, bm.getWidth(), bm.getHeight(), mtx, false);
        deg=deg+1; //deg=0 in beginning
        bm=rotatedBMP;
    }   
}

This method is written in the class of ball, which is internally called by another method move(). The bitmap bm is not rotating as I wanted. It's just falling out of the screen, which seems like the size of bitmap has increased. And I've to force close it after few seconds.
I've seen other rotate bitmap questions, but they are not working for me too. Thanks in advance.

Answer 1

You are rotating the Matrix with the same value ( 10 ) all the time. That is why the ball is not rotating. Do the following instead: mtx.postRotate(deg);

Also, a general remark: I guess you are drawing the resulting rotated ball bm ? If you are drawing the ball in a different thread then the first thing you should look at is to make sure your threads have exclusive access to bm so that you won't be rendering the ball while it is being affected a new value at bm=rotatedBMP;

Answer 2

Anyways found the answer by myself. The code I am using now is as follows (for those who are having same problem)

Matrix mtx=new Matrix();
mtx.postRotate(deg,25,25);
mtx.postTranslate(x, y);
c.drawBitmap(bm, mtx, paint);
deg=deg-10;

The code is running fine now. Thanks anyways.