//Two useful shader snippets

//convert V from cartesian coordinates to polar coordinates (stored in UV)
float yaw = 0.0;
yaw = atan2(V.x,V.z) / 6.28318531 - 0.25;
float pitch = asin(V.y) / 1.57079633;
uv = vec2(yaw,abs(pitch));
vec3 cielo = texture2DLod(reflection, uv,0.0);


//How to project vertex to screen in normalized coordinates (useful for reflections)
//in the vertex shader send this in a varying
screen_pos = gl_ModelViewProjectionMatrix * gl_Vertex;
//and in the pixel shader
screen_pos.xy = (screen_pos.xy / screen_pos.w) * 0.5 + vec2(0.5,0.5);