Pixel Image Collision
BlitzMax Forums/BlitzMax Programming/Pixel Image Collision
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| Is there a way to test for a collision between a pixal and an image? |
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The easiest way would be to read a pixel from it and decide. Also, I use it on a pixmap rather than an image:Function Collided%(px#, py#, pix:TPixmap, imgx#, imgy#) Local _x# = px - imgx 'bring coords in pixmap space Local _y# = py - imgy if (_x < 0) Return False if (_x > pix.width) Return False if (_y < 0) Return False if (_y > pix.height) Return False Return ((pix.GetPixel(_x, _y) Shr 24) < $0F) End Function Now to explain that last line of code: GetPixel returns a pixel in the form of a 32 bit integer, with 8 bits for each of Red, Green, Blue and Alpha components. Shr shifts the whole value right 24 bits. That strips the RGB and leave the Alpha. Then I just measure it against a low value (might as well be 0) to give it a small threshold. Some images don't have precisely 0 alpha and that might register a collision everywhere on the image. Limitations of this particular code: - Does not take into account the scale/rotation of the image - requires the pixmap to be in PF_RGBA format. I always convert them to this format upon loading. This speeds up the rest of my code because it's targeted at this format. The other approch, a bit slower, would be to use CollideImages or CollideImages2 with your image and a 1x1 image for your "pixel". |
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| Awesome thanks a lot Jim! I've been using the 1x1 image technique and it works! I just thought there might be a "better" way to do it. I'm glad I asked because it gives me something new to learn, Literals :) |
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