naive normal direction

exercise2/glsl/terrain.vert

@@ -113,5 +113,12 @@ vec3 calculate_normal(vec4 terrain_position) {
 	vec3 p2 = (points[1] - terrain_position).xyz;
 
 	// calculate normal
-	return normalize(cross(p1, p2));
+	vec3 normal = normalize(cross(p1, p2));
+
+	// naively assume that a normal always has to look upwards
+	if (normal.y < 0.0) {
+		return -normal;
+	} else {
+		return normal;
+	}
 }