Android scale ImageView using anchor points

Question

The goal is: the Imageview have 4 squares on each corners. If the user touch and drag one of this, the image is scaled.

Given the image, the 4 squares and the touched square how can i implement this feature?
(square = Rectf class)

example of image

Answer 1

I have find out a possible solution, if anyone need the code:

float centerX, centerY, startScale, startX, startY;

private void startScaling(MotionEvent e) {
    ImageView imageView = (ImageView) getChildAt(0);

    switch (e.getAction()) {
        case MotionEvent.ACTION_DOWN:
            startX = e.getX();
            startY = e.getY();
            startScale = imageView.getScaleX();
            centerX = imageView.getX() + imageView.getWidth() / 2F;
            centerY = imageView.getY() + imageView.getHeight() / 2F;
            break;

        case MotionEvent.ACTION_MOVE:
            // euclidean distance
            double length1 = Point.distance(centerX, centerY, startX, startY);
            double length2 = Point.distance(centerX, centerY, e.getX(), e.getY());

            if(length2 > length1) {
                //scale up
                float scaleFactor = (float) (length2 / length1);

                //scale the image
                imageView.setScaleX(startScale * scaleFactor);
                imageView.setScaleY(startScale * scaleFactor);
            }else {
                //scale down
                // calculate the scale factor
                float scaleFactor = (float) (length1 / length2);

                // scale the image
                imageView.setScaleX(startScale / scaleFactor);
                imageView.setScaleY(startScale / scaleFactor);
            }

            float scaledWidth = imageView.getWidth() * imageView.getScaleX();
            float scaledHeight = imageView.getHeight() * imageView.getScaleY();

            // calculate new boubds of the image
            float left = centerX - scaledWidth / 2F;
            float top = centerY - scaledHeight / 2F;
            float right = left + scaledWidth;
            float bottom = top + scaledHeight;
            break;
        case MotionEvent.ACTION_UP:
            break;
    }
}