Android: How to rotate a bitmap on a center point
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? :)
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 ~frameworks\base\graphics\java\android\graphics\Bitmap.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.
Edited: optimized code.
public static Bitmap RotateBitmap(Bitmap source, float angle)
{
Matrix matrix = new Matrix();
matrix.postRotate(angle);
return Bitmap.createBitmap(source, 0, 0, source.getWidth(), source.getHeight(), matrix, true);
}
To get Bitmap from resources:
Bitmap source = BitmapFactory.decodeResource(this.getResources(), R.drawable.your_img);