mirror of
https://github.com/kovidgoyal/kitty
synced 2026-07-11 18:32:12 +02:00
55 lines
2.1 KiB
GLSL
55 lines
2.1 KiB
GLSL
#pragma kitty_include_shader <linear2srgb.glsl>
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uniform sampler2D image;
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uniform vec2 src_size; // Source texture size in pixels
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in vec2 texcoord;
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out vec4 output_color;
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void main() {
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// The input texture contains sRGB colors with premultiplied alpha.
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// We need to output unpremultiplied sRGB colors with proper downscaling.
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// For proper downscaling, we need to:
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// 1. Sample neighboring pixels
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// 2. Convert from sRGB to linear (unpremultiplying first)
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// 3. Average in linear space
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// 4. Convert back to sRGB
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// 5. Output unpremultiplied
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// Calculate the texel size
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vec2 texel_size = 1.0 / src_size;
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// Sample a 2x2 grid for better quality downscaling
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// This provides basic bilinear-like filtering in linear space
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vec2 tc = texcoord;
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vec4 s00 = texture(image, tc + vec2(-0.25, -0.25) * texel_size);
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vec4 s10 = texture(image, tc + vec2( 0.25, -0.25) * texel_size);
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vec4 s01 = texture(image, tc + vec2(-0.25, 0.25) * texel_size);
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vec4 s11 = texture(image, tc + vec2( 0.25, 0.25) * texel_size);
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// Unpremultiply and convert to linear for each sample
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vec3 linear00 = s00.a > 0.0 ? srgb2linear(s00.rgb / s00.a) : vec3(0.0);
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vec3 linear10 = s10.a > 0.0 ? srgb2linear(s10.rgb / s10.a) : vec3(0.0);
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vec3 linear01 = s01.a > 0.0 ? srgb2linear(s01.rgb / s01.a) : vec3(0.0);
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vec3 linear11 = s11.a > 0.0 ? srgb2linear(s11.rgb / s11.a) : vec3(0.0);
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// Average the alpha values
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float avg_alpha = (s00.a + s10.a + s01.a + s11.a) * 0.25;
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// For proper downsampling with transparency, weight colors by their alpha
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// This ensures partially transparent pixels contribute proportionally
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vec3 weighted_sum = linear00 * s00.a + linear10 * s10.a + linear01 * s01.a + linear11 * s11.a;
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float total_weight = s00.a + s10.a + s01.a + s11.a;
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// Calculate the weighted average color in linear space
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vec3 avg_linear = total_weight > 0.0 ? weighted_sum / total_weight : vec3(0.0);
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// Convert back to sRGB
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vec3 srgb_color = linear2srgb(avg_linear);
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// Output unpremultiplied sRGB color
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output_color = vec4(srgb_color, avg_alpha);
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}
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