const float PI =  3.14159265;

varying vec4	Color;

void
main( void )
{
	Color = gl_Color;

	vec4 pos = gl_ModelViewMatrix * gl_Vertex;
	float lenxy = length( pos.xy );

	if( lenxy != 0.0 )
	{
		float phi = atan( lenxy, -pos.z );
		float r_over_len = (  phi / (PI/2.)  )  /  lenxy;
		pos.xy = pos.xy * r_over_len;
	}

	gl_Position = gl_ProjectionMatrix * pos;
}