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April 29, 2020 14:28
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Sprite sheet/texture atlas sampling in OpenGL/GLSL with Shadron
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| // Sprite sheet/texture atlas sampling in OpenGL/GLSL with Shadron | |
| // (c) 2020 Mick Dekkers | |
| // This work is licensed under the terms of the MIT license. See https://opensource.org/licenses/MIT for a copy. | |
| // Tested with the emoji spritesheets at https://github.com/iamcal/emoji-data , specifically: | |
| // https://github.com/iamcal/emoji-data/blob/8930a29f7193cc7603765c9046edac7ca529de78/sheets-clean/sheet_apple_64_clean.png | |
| parameter int outputSize = 300.0 : range(1, 1024); | |
| parameter int spriteSize = 64 : range(1, 1024); | |
| parameter int spritePadding = 2 : range(1, 100); | |
| parameter int numSpritesPerDimension = 56 : range(1, 1024); | |
| parameter ivec2 spriteIndex = ivec2(0, 0) : range(ivec2(0, 0), ivec2(56, 56)); | |
| parameter bool halfPixelCorrection = true; | |
| // The input image - clamp so that edges don't wrap around | |
| image Input = file() : map(clamp); | |
| // The output image shader | |
| glsl vec4 sampleSpriteSheet(vec2 position) { | |
| vec2 sheetSize = vec2(textureSize(Input, 0)); | |
| vec2 spriteSizeInTextureSpace = spriteSize / sheetSize; | |
| vec2 spritePaddingInTextureSpace = spritePadding / sheetSize; | |
| // GLSL coordinates are bottom-up, but the sprite index is top-down | |
| ivec2 correctedSpriteIndex = ivec2(spriteIndex.x, numSpritesPerDimension - spriteIndex.y); | |
| vec2 texCoord = position + | |
| spriteSizeInTextureSpace * correctedSpriteIndex * numSpritesPerDimension + | |
| spritePaddingInTextureSpace * correctedSpriteIndex * numSpritesPerDimension; | |
| vec2 scaledTexCoord = texCoord / numSpritesPerDimension; | |
| vec2 halfPixelCorrectedTexCoord = halfPixelCorrection ? (scaledTexCoord - vec2(0.5) / sheetSize) : scaledTexCoord; | |
| return texture2D(Input, halfPixelCorrectedTexCoord); | |
| } | |
| // The output image | |
| image Output = glsl(sampleSpriteSheet, outputSize); | |
| export png(Output, "output.png"); |
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