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Optimize isTouchingDrawables? #18
Description
Update: See #18 (comment)
As you know, TurboWarp is all about speeding up Scratch projects, so when I saw a function, isTouchingDrawables, with this comment...
scratch-render/src/RenderWebGL.js
Lines 1274 to 1275 in dd5d399
...I saw potential for improvement.
If I'm understanding the code right, Scratch checks for collisions between every single pixel to be sure that the sprites appear to be precisely touching each other. This can slow things down a lot when overused.
Instead of colliding individual pixels, combining groups of pixels to form rectangles, as shown in the video below, would reduce the number of regions that need to be accounted for, increasing performance in the long run.
optimized.touching.detector.webm
Some projects may see performance improvements of over 10x or even 50x in circumstances that would normally cause lag spikes.
Activity
DNin01 commentedon Oct 4, 2025
Well, my video doesn't exactly demonstrate how Scratch's touching detection works, but it probably gives you an idea of what we're dealing with here.
DNin01 commentedon Oct 4, 2025
It looks like Scratch scans the region encompassing all touching candidates—the sprites (including clones) that need to be checked.
union.touching.detector.webm
I may still be wrong about that, but just scanning bounding box intersections between the base sprite and the candidates without using unities might be faster.
intersect.touching.detector.webm
GarboMuffin commentedon Oct 4, 2025
it works like your last video