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Asked: 2026-05-29T05:09:20+00:00

I have a flat plane of 2D graphics with a camera pointing at them.

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I have a flat plane of 2D graphics with a camera pointing at them. I want to get the effect so when a user pinches and zooms, it looks like they anchored their fingers on the plane and can pinch zoom realistically. To do this, I need to calculate the the distance between their fingers into distance in 3D space (which I already can do), but then I need to map that 3D distance to a z value.

For example, if a 100 units wide square and shrunk to 50 units (50%), how much further back would the camera need to move to make that 100 unit square shrink by half?

So to put it simply, If I have the distance in 3D space, how do I calculate the distance of the camera needed to shrink that 3D space by a certain amount?

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  1. Editorial Team

    EDIT:

    So, I tried it myself and came up with this formula:

    So let’s say you are 1 unit away from the object.
    When you want to shrink it to 50% (zoomfactor) the new distance equals 2 units => 1 / 0.5 = 2. The camera must be twice as far away.

    Moving the camera closer to the plane for zooming only works with a perspective projection. The absolute distance depends on the angle of view. Usually you zoom by reducing the angle of view and not moving the camera at all.

    If you are using an orthographic projection you can simply adjust the field of view / scale the projection matrix.

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