sampler2D img;
sampler2D bkd : register(s1);

float4 ps_main(in float2 In : TEXCOORD0) : COLOR0	{
	float4 L = tex2D(img,In);
	float4 B = tex2D(bkd,In);
	return B<0.5?(2.0*B*L):(1.0-2.0*(1.0-B)*(1.0-L));
}

technique tech_main	{ pass P0 { PixelShader = compile ps_2_0 ps_main(); }  }