vertex shader data flow



  struct vsinput {
      float4 position : POSITION; 
      float3 normal : NORMAL; 
      float2 uv : TEXCOORD0;
  };
  struct vsoutput {
      float4 position   : POSITION;   // vertex position 
      float4 color    : COLOR0;     // vertex diffuse color
      float2 uv  : TEXCOORD0;  // vertex texture coords 
  };