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Asked: 2026-06-01T01:50:26+00:00

I’m trying to check if two objects (e.g. a rectangle and a triangle) on

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I’m trying to check if two objects (e.g. a rectangle and a triangle) on a HTML5 canvas are overlapping each other.

Currently I can only check that by looking at the screen (having set globalCompositeOperation=’lighter’).

My first idea would have been to scan all over the canvas if the “lighter” (compare code snippet above) color exists in the canvas. But therefor I would have to look at every single pixel which was rather costly for what I need.

Is there a (better) alternative to automatically check if they are overlapping?

Best regards.

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1 Answer

  1. Editorial Team

    The site below explains how to use the Separating Axis Theorem to determine if two convex shapes overlap.

    http://www.codezealot.org/archives/55

    To use this you will need to know the coordinate data used in contstructing the shapes.

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