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// SPDX-FileCopyrightText: Copyright 2025 Eden Emulator Project
// SPDX-License-Identifier: GPL-3.0-or-later
// https://en.wikipedia.org/wiki/Lanczos_resampling
#version 460 core
layout (location = 0) in vec2 frag_tex_coord;
layout (location = 0) out vec4 color;
layout (binding = 0) uniform sampler2D color_texture;
#define PI 3.1415926535897932384626433
float sinc(float x) {
return x == 0.0f ? 1.0f : sin(PI * x) / (PI * x);
}
float lanczos(vec2 v, float a) {
float d = length(v);
return sinc(d) / sinc(d / a);
}
vec4 textureLanczos(sampler2D textureSampler, vec2 p) {
vec3 c_sum = vec3(0.0f);
float w_sum = 0.0f;
vec2 res = vec2(textureSize(textureSampler, 0));
vec2 cc = floor(p * res) / res;
// kernel size = (2r + 1)^2
const int r = 3; //radius (1 = 3 steps)
#define LANCZOS_LOOP_STEP(x, y) \
{ \
vec2 kp = 0.5f * (vec2(x, y) / res); /* 0.5 = half-pixel level resampling */ \
vec2 uv = cc + kp; \
float w = lanczos(kp, float(r)); \
c_sum += w * texture(textureSampler, p + kp).rgb; \
w_sum += w; \
}
for (int y = -r; y <= r; ++y) {
LANCZOS_LOOP_STEP(-3, y);
LANCZOS_LOOP_STEP(-2, y);
LANCZOS_LOOP_STEP(-1, y);
LANCZOS_LOOP_STEP(-0, y);
LANCZOS_LOOP_STEP(+1, y);
LANCZOS_LOOP_STEP(+2, y);
LANCZOS_LOOP_STEP(+3, y);
}
return vec4(c_sum / w_sum, 1.0f);
}
void main() {
color = textureLanczos(color_texture, frag_tex_coord);
}
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