varying vec4 texcoord;
void main ()
{
  gl_Position.zw = (gl_Vertex.xy * 2.0);
  gl_Position.xy = gl_Vertex.xy;
  texcoord.x = gl_Vertex.z;
  texcoord.yz = gl_Vertex.zw;
  texcoord.w = gl_Vertex.x;
}