ADD: IBL glsl cleaning

shaders/ibl_common.glsl

@@ -0,0 +1,57 @@
+#ifndef IBL_COMMON_GLSL
+#define IBL_COMMON_GLSL
+
+// IBL bindings (set=3): specular equirect 2D, BRDF LUT, SH UBO.
+layout(set=3, binding=0) uniform sampler2D iblSpec2D;
+layout(set=3, binding=1) uniform sampler2D iblBRDF;
+layout(std140, set=3, binding=2) uniform IBL_SH { vec4 sh[9]; } iblSH;
+
+// Evaluate diffuse irradiance from 2nd-order SH coefficients (9 coeffs).
+// Coefficients are pre-convolved with the Lambert kernel on the CPU.
+vec3 sh_eval_irradiance(vec3 n)
+{
+    float x = n.x, y = n.y, z = n.z;
+    const float c0 = 0.2820947918;
+    const float c1 = 0.4886025119;
+    const float c2 = 1.0925484306;
+    const float c3 = 0.3153915653;
+    const float c4 = 0.5462742153;
+    float Y[9];
+    Y[0] = c0;
+    Y[1] = c1 * y;
+    Y[2] = c1 * z;
+    Y[3] = c1 * x;
+    Y[4] = c2 * x * y;
+    Y[5] = c2 * y * z;
+    Y[6] = c3 * (3.0 * z * z - 1.0);
+    Y[7] = c2 * x * z;
+    Y[8] = c4 * (x * x - y * y);
+    vec3 r = vec3(0.0);
+    for (int i = 0; i < 9; ++i)
+    {
+        r += iblSH.sh[i].rgb * Y[i];
+    }
+    return r;
+}
+
+// Map direction to equirectangular UV (same convention across shaders).
+vec2 dir_to_equirect(vec3 d)
+{
+    d = normalize(d);
+    float phi = atan(d.z, d.x);
+    float theta = acos(clamp(d.y, -1.0, 1.0));
+    // 1/(2*pi) = 0.15915494309, 1/pi = 0.31830988618
+    return vec2(phi * 0.15915494309 + 0.5, theta * 0.31830988618);
+}
+
+// Helper for selecting mip LOD from roughness and available levels.
+// Uses roughness^2 to bias towards blurrier reflections at mid roughness.
+float ibl_lod_from_roughness(float roughness, float levels)
+{
+    float maxLevel = max(levels - 1.0, 0.0);
+    float r = clamp(roughness, 0.0, 1.0);
+    return r * r * maxLevel;
+}
+
+#endif // IBL_COMMON_GLSL
+