# Scale around a point

I am trying to create an image editing application for the purpose of generating UV maps in my own format. I am currently working on scaling the image for the purpose of zooming. I can get the image to zoom correctly, but it always zooms around the center of the image. I would like to scale around the mouse instead.

My Question

How can I scale a rectangle(image) around a point(the mouse)?

My Variables

float X = imgX;
float Y = imgY;
float W = imgWidth;
float H = imgHeight;
float mX = mouseX;
float mY = mouseY;


My Code

function scale(float ratio){
W += ratio;
H += ratio;
X -= ratio/2;
Y -= ratio/2;
}


To Clarify

I am not trying to change camera or view-port. I am trying to scale an BufferedImage through the Graphics.drawImage() function. The function take the image and the x, y, width, and height of the image to be rendered.

Example In the Windows Photo Viewer, when you zoom in using mouse scroll, the image is zoomed around the mouse.

You can't. Scaling is just applying a coefficient to all coordinates, it doesn't take the coordinate of the camera into account.

If what i understood is right, the visual effect you want imply to move the camera toward the coordinate of the mouse as you zoom.

You can achieve this by translating the image on the directed vector (mousePointer, centerOfTheScreen) and by the same time translating the cursor with the opposite vector.

• I am not trying to change the camera, as I am not working with cameras right now. I am trying to change the size of a rectangle(non exact) and make it change size proportionally around a point which will be the mouse on the screen. Sep 2, 2014 at 18:51
• @TheHarrisonCrafter Yep OK, but read this answer carefully again. The linear transformation of scaling is defined relative to the origin. You need to combine them to scale around a point. You can also translate an image, but that's a different transformation. Some high-level graphics APIs expose a scale method which can optionally take a point too, but all that's really doing internally is applying an additional translate-operation.
– Anko
Sep 2, 2014 at 22:56