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graphics: Improve roundTexel implementation

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Hajime Hoshi 2017-12-07 03:24:46 +09:00
parent 1152439e65
commit 7b74a8f29f
1 changed files with 8 additions and 6 deletions
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14
internal/graphics/shader.go
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@ -71,12 +71,14 @@ varying vec2 varying_tex_coord_min;
varying vec2 varying_tex_coord_max;
vec2 roundTexel(vec2 p) {
// Many devices can't use highp in fragment shaders, so use only mediump here.
// According to the spec, mediump value range is -2**14 to 2**14 (16384).
// Some machines have higher precisions, but a very slight value difference causes
// a different result of getColorAt. This function avoids such flakines by rounding values.
float max_mediump = 16384.0;
return floor(p * max_mediump + 0.5) / max_mediump;
vec2 factor = 1.0 / (source_size * 256.0);
if (factor.x > 0.0) {
p.x -= mod(p.x + factor.x * 0.5, factor.x) - factor.x * 0.5;
}
if (factor.y > 0.0) {
p.y -= mod(p.y + factor.y * 0.5, factor.y) - factor.y * 0.5;
}
return p;
}
vec4 getColorAt(vec2 pos) {