Question

I’m struggling to draw a rotating bitmap around its center and do the rotating without resizing the bitmap. I’m drawing all my sprites to the screen via a game thread, so I’m looking for a solution that incorporates the original bitmap and not the canvas.

Thanks in advance.

This is my code so far, it turns a bitmap around its center, yet resizes it.

i = i + 2;
            transform.postRotate(i, Assets.scoresScreen_LevelStar.getWidth()/2, Assets.scoresScreen_LevelStar.getHeight()/2);
            Bitmap resizedBitmap = Bitmap.createBitmap(Assets.scoresScreen_LevelStar, 0, 0, Assets.scoresScreen_LevelStar.getWidth(), Assets.scoresScreen_LevelStar.getHeight(), transform, true);

            game.getGraphics().getCanvasGameScreen().drawBitmap(resizedBitmap, null, this.levelStar.getHolderPolygons().get(0), null);

Update:

I’ve noticed this isn’t as easy as it sounds. My rotating code is not the problem. The bitmap rotates, yet the dst rect will also have to increase/decrease depending on the angle of rotation, or else the bimap will appear smaller, since it’s drawn into a fixed dst rect.
So I’m guessing I’ll have to develop some method that will return a dst rect.
So the methods needed to rotate a bitmap without appeared resizing:

public static Bitmap rotateBitmap(Bitmap bitmap, int rotation) // I've got this method working

and

public static Rect rotateRect(Rect currentDst, int rotation) // Don't got this

I understand this will require some math (trig), anyone up for the challenge? 😛

Answer 1

This worked for me!

I created a method that returns a matrix. The matrix can be used in the following drawing method:

public void drawBitmap (Bitmap bitmap, Matrix matrix, Paint paint)

Here you go! (The parameter shape can be replaced with ease, if you would like that, just leave a comment):

public static Matrix rotateMatrix(Bitmap bitmap, Shape shape, int rotation) {

        float scaleWidth = ((float) shape.getWidth()) / bitmap.getWidth();
        float scaleHeight = ((float) shape.getHeight()) / bitmap.getHeight();

        Matrix rotateMatrix = new Matrix();
        rotateMatrix.postScale(scaleWidth, scaleHeight);
        rotateMatrix.postRotate(rotation, shape.getWidth()/2, shape.getHeight()/2);
        rotateMatrix.postTranslate(shape.getX(), shape.getY());


        return rotateMatrix;

    }

NB: If you want an animated rotation, the rotation parameter will have to be updated with new values every frame eg. 1 then 2 then 3 …