[vk, opengl] add lanczo and spline-1 filtering (#2534)

Signed-off-by: lizzie <lizzie@eden-emu.dev>
Reviewed-on: https://git.eden-emu.dev/eden-emu/eden/pulls/2534
Reviewed-by: MaranBr <maranbr@eden-emu.dev>
Reviewed-by: Shinmegumi <shinmegumi@eden-emu.dev>
Reviewed-by: Maufeat <sahyno1996@gmail.com>
Co-authored-by: lizzie <lizzie@eden-emu.dev>
Co-committed-by: lizzie <lizzie@eden-emu.dev>

1 files changed, 48 insertions, 0 deletions

diff --git a/tools/lanczos_gen.c b/tools/lanczos_gen.c
new file mode 100644
index 0000000000..6d7be3cb0e
--- /dev/null
+++ b/tools/lanczos_gen.c
@@ -0,0 +1,48 @@
+// SPDX-FileCopyrightText: Copyright 2025 Eden Emulator Project
+// SPDX-License-Identifier: GPL-3.0-or-later
+
+// clang -lm tools/lanczos_gen.c -o tools/lanczos_gen && ./tools/lanczos_gen
+#include <stdio.h>
+#include <math.h>
+
+double sinc(double x) {
+    return x == 0.0f ? 1.0f : sin(M_PI * x) / (M_PI * x);
+}
+
+typedef struct vec2 {
+    double x;
+    double y;
+} vec2;
+
+double lanczos(vec2 v, float a) {
+    double d = sqrt(v.x * v.x + v.y * v.y);
+    return sinc(d) / sinc(d / a);
+}
+
+int main(int argc, char* argv[]) {
+    const int r = 3; //radius (1 = 3 steps)
+    const int k_size = (r * 2 + 1) * (r * 2 + 1);
+    double w_sum = 0.0f;
+    // kernel size = (r * 2 + 1) ^ 2
+    printf("const float w_kernel[%i] = float[] (\n    ", k_size);
+    double factor = 1.0f / ((double)r + 1.0f);
+    for (int x = -r; x <= r; x++)
+        for (int y = -r; y <= r; y++) {
+            double w = lanczos((vec2){ .x = x, .y = y }, (double)r);
+            printf("%lff, ", w);
+            w_sum += w;
+        }
+    printf("\n);\n");
+    printf("const vec2 w_pos[%i] = vec2[] (\n    ", k_size);
+    for (int x = -r; x <= r; x++)
+        for (int y = -r; y <= r; y++) {
+            vec2 kp = (vec2){
+                .x = x * factor,
+                .y = y * factor
+            };
+            printf("vec2(%lff, %lff), ", kp.x, kp.y);
+        }
+    printf("\n);\n");
+    printf("const float w_sum = %lff;\n", w_sum);
+    return 0;
+}