Mostly complete from the Python original

src/gl/mesh.frag

@@ -0,0 +1,15 @@
+#version 120
+
+varying vec3 ec_pos;
+
+void main() {
+    vec3 base3 = vec3(0.99, 0.96, 0.89);
+    vec3 base2 = vec3(0.92, 0.91, 0.83);
+    vec3 base00 = vec3(0.40, 0.48, 0.51);
+    vec3 ec_normal = normalize(cross(dFdx(ec_pos), dFdy(ec_pos)));
+    float a = dot(ec_normal, vec3(0.0, 0.0, 1.0));
+    float b = dot(ec_normal, vec3(-0.57, -0.57, 0.57));
+
+    gl_FragColor = vec4((a*base2 + (1-a)*base00)*0.5 +
+                        (b*base3 + (1-b)*base00)*0.5, 1.0);
+}