float4 main( float4 color_in : COLOR0, 
             float2 texCoord_in : TEXCOORD0,
             uniform sampler2D diffuseMap : register(S0) ) : COLOR0
{
   float distance = tex2D(diffuseMap, texCoord_in).a;
   const float w = 0.5/3;
   const float threshold = 0.5f;
   float alpha = smoothstep( threshold-w, threshold+w, distance );
   return float4(color_in.rgb,alpha * color_in.a);
}