Zoom in on a point (using scale and translate)

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The better solution is to simply move the position of the viewport based on the change in the zoom. The zoom point is simply the point in the old zoom and the new zoom that you want to remain the same. Which is to say the viewport pre-zoomed and the viewport post-zoomed have the same zoompoint relative to the viewport. Given that we’re scaling relative to the origin. You can adjust the viewport position accordingly:

scalechange = newscale - oldscale;
offsetX = -(zoomPointX * scalechange);
offsetY = -(zoomPointY * scalechange);

So really you can just pan over down and to the right when you zoom in, by a factor of how much you zoomed in, relative to the point you zoomed at.

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