ActionScript 2.0 :: Bitmap Hit Testing - Pixel Perfect Collisions
Mar 31, 2007
I have been desperately searching for a way to do pixel perfect collisions, and for someone to explain it to me in detail. explain the code in the .fla file, posted by the Canadian in the frequently asked questions thread on bitmapData hit testing:
[Code]...
after looking through the help files, i must admit they are terribly vague. All you are doing is checking if _alpha is above a certain amount. With movieClips you would use 0->100 but with this hittest you have to use 0->255 (0x00->0xFF)so an _alpha of 50 would correspond to approx 128 (0x80). Nearly all the time you could just use 1 as a hittest parameter so you are checking for any hit at all but maybe you have a shadow in a mc layer and you do not want to check a hit. This is when you might be able to use your threshold parameter. In other words, the hit test will only react to parts of the bitmap which have a greater or equal alpha than the alpha threshold, mostly useful for a shadow.
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I just thought I'd drop a note here to those who are interested. I recently posted about it on my website and you can download the source for it there too. Here's some excerpts:
Ive run it at 60+ FPS with 7,000 particles, but that actually isnt the limitation (unless your particles are crunching heavy math for eg movement). Rather its the size and number of sprites that were colliding with the particles.
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