SuperTuxKart 1.5 upstream source (from official release tarball)

data/shaders/utils/encode_normal.frag

@@ -0,0 +1,17 @@
+// Octahedron Normal Vector 
+
+vec2 OctWrap(vec2 v)
+{
+    vec2 w = 1.0 - abs( v.yx );
+    if (v.x < 0.0) w.x = -w.x;
+    if (v.y < 0.0) w.y = -w.y;
+    return w;
+}
+
+vec2 EncodeNormal(vec3 n)
+{
+    n /= (abs(n.x) + abs(n.y) + abs(n.z));
+    n.xy = n.z >= 0.0 ? n.xy : OctWrap(n.xy);
+    n.xy = n.xy * 0.5 + 0.5;
+    return n.xy;
+}