Zoom a bitmap with drawBitmap and rectangles - And

Question

I'm developing a small image editor. Basically, the user can insert some images in a canvas, and through interaction with the fingers moving them around. I'm having some trouble with the Zooming. I have followed the idea of this tutorial to use a bitmap, and to apply transformations to two rectangles. Afterwards, if we draw the bitmap over the canvas with android.graphics.Canvas.drawBitmap(Bitmap bitmap, Rect src, Rect dst, Paint paint), the transformation is applied. So far, is not working for me.

I store all the images in an array of images, ColorBall. When I detect there is a zoom gesture, and only if it was over a certain image (this works so far), I apply over that image the transformations (the values are dummy, just wanted to check if it works):

colorballs.get(balID-1).getmRectDst().left   = getLeft();
colorballs.get(balID-1).getmRectDst().top    = getTop();
colorballs.get(balID-1).getmRectDst().right  = getRight();
colorballs.get(balID-1).getmRectDst().bottom = getBottom();

colorballs.get(balID-1).getmRectSrc().left   += 10;
colorballs.get(balID-1).getmRectSrc().top    += 10;
colorballs.get(balID-1).getmRectSrc().right  += 10;
colorballs.get(balID-1).getmRectSrc().bottom += 10;

On the OnDraw event, for all the pictures in the array I locate them, and then I scale them using the rectangles. So far, the part of scaling is not working:

//draw the balls on the canvas
for (ColorBall ball : colorballs) {
    canvas.drawBitmap(ball.getBitmap(), ball.getX(), ball.getY(), null);
    canvas.drawBitmap(ball.getBitmap(), ball.getmRectSrc(), ball.getmRectDst(), mPaintBalls);
}

Any suggestion of what can I be missing here? Thanks in advance!

Answer 1

It looks like you are adding to the bottom/right, so instead of zooming you are actually just shifting the background source to the right ten.

colorballs.get(balID-1).getmRectSrc().right  -= 10;
colorballs.get(balID-1).getmRectSrc().bottom -= 10;