SuperTuxKart 1.5 upstream source (from official release tarball)

data/shaders/ge_shaders/utils/sun_direction.glsl

@@ -0,0 +1,14 @@
+// Sun Most Representative Point (used for MRP area lighting method)
+// From "Frostbite going PBR" paper
+
+vec3 sunDirection(vec3 R, vec3 sun_direction, float sun_angle_tan_half, mat4 inverse_view_matrix)
+{
+    sun_direction = normalize((transpose(inverse_view_matrix) * vec4(sun_direction, 0.)).xyz);
+    float DdotR = dot(sun_direction, R);
+    vec3 S = normalize(R - DdotR * sun_direction);
+    float sun_angle_tan_half2 = 1 + sun_angle_tan_half * sun_angle_tan_half;
+    vec2 sun_angle_sin_cos = vec2(2 * sun_angle_tan_half, 2 - sun_angle_tan_half2) / sun_angle_tan_half2;
+    // Equivalent to DdotR < cos(sun_angle)
+    float factor = step(DdotR, sun_angle_sin_cos.y);
+    return mix(R, normalize(sun_direction * sun_angle_sin_cos.y + S * sun_angle_sin_cos.x), factor);
+}