SuperTuxKart 1.5 upstream source (from official release tarball)

data/shaders/utils/SpecularIBL.frag

@@ -0,0 +1,11 @@
+uniform samplerCube probe;
+
+vec3 SpecularIBL(vec3 normal, vec3 V, float roughness)
+{
+    vec3 sampleDirection = reflect(-V, normal);
+    sampleDirection = (u_inverse_view_matrix * vec4(sampleDirection, 0.)).xyz;
+
+     // Assume 8 level of lod (ie 256x256 texture)
+    float lodval = 7. * (1. - roughness);
+    return clamp(textureLod(probe, sampleDirection, lodval).rgb, 0., 1.);
+}