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2D Camera Zoom

Started by GameDevMan Jan 3, 2009 at 1:08 PM 1 replies 5.2k views

Original Post

Jan 3, 2009 at 1:08 PM

I made this harder than it needs to be by programming the engine in the way I did, but here's my question. I want to create a simple zooming effect with 2D sprites -- simply making the on-screen picture larger or smaller with no "pseudo-3D". I'm stuck on what kind of math to apply in order to get the camera to zoom in, but still stay on "target", as simply blowing out the vectors will throw the camera off-center. With my engine, (0,0) is the Top-Left corner of the screen as opposed to the center. Changing the Camera X higher will move the image to the left. I've successfully gotten the image to zoom in and out, but my only problem is to keep the camera 'centered' on its target. CameraZoom = 1 means that the image isn't zoomed. CameraZoom = 2 means that the image is scaled x2. CameraZoom = .5 means that the image is "x2" away. If anymore clarification is needed, let me know. Thanks a lot in advance. [Edited by - Rokkuman on January 3, 2009 1:43:36 PM]

HappyCoder

Jan 3, 2009 at 7:55 PM

I think you can do it like this.

screenCoords = zoom * (worldCoord - worldOffset) + screenCenter;

where

worldCoord is a point in the 2D scene to convert to screen coordinates
worldOffset is the offset of the world in world units
zoom is a number representing the zoom level
screenCenter is the zoom center on the screen or where the camera will zoom in and out on. You will probably just want to use (screenWidth / 2, screenHeight / 2)

Now you just need to take any points in the scene and pass them through those transformations. If you also need to transform dimensions, use this.

screenSize = zoom * size;

erissian

Jan 3, 2009 at 8:21 PM

Without knowing more about how you track and handle the data, my best suggestion is that you scale the camera position inversely. That is, if everything is scaled by 2, then the camera position will also be scaled by 2. In order to translate it back to the absolute screen coordinates, you will have to divide it by 2.

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