struct Output {
  float4 position : POSITION;
  float3 color    : COLOR;
};

Output vert_shader(float3 position : POSITION,
				   float3 color    : COLOR,
				   uniform float twisting)
{	
  Output OUT;

  float angle = twisting * length(position);
  float cosLength, sinLength;
  sincos(angle, sinLength, cosLength);
  OUT.position[0] = cosLength * position[0] +
                   -sinLength * position[1];
  OUT.position[1] = sinLength * position[0] +
                    cosLength * position[1];
  OUT.position[2] = 0;
  OUT.position[3] = 1;
  OUT.color = color;
  return OUT;	
}