// YV12 Chroma Upsampling=ps_2_0
// http://forum.doom9.org/showthread.php?p=1184975

/*
YV12 chroma upsampling fixer
by Kurt Bernhard 'Leak' Pruenner

Use with YV12 output if the half-resolution chroma 
gets upsampled in hardware by doubling the values
instead of interpolating between them.

(i.e. if you're getting blocky red edges on dark 
backgrounds...)
*/

sampler s0 : register(s0);
float4 p0 : register(c0);
float4 p1 : register(c1);

#define width (p0[0])
#define height (p0[1])

float4 getPixel(float2 tex, float dx, float dy)
{
    tex.x+=dx;
    tex.y+=dy;
    
    return tex2D(s0, tex);
}

float4 rgb2yuv(float4 rgb)
{
    float4x4 coeffs=
        {
             0.299, 0.587, 0.114, 0.000,
            -0.147,-0.289, 0.436, 0.000,
             0.615,-0.515,-0.100, 0.000,
             0.000, 0.000, 0.000, 0.000
        };
        
    return mul(coeffs,rgb);
}

float4 yuv2rgb(float4 yuv)
{
    float4x4 coeffs=
        {
             1.000, 0.000, 1.140, 0.000,
             1.000,-0.395,-0.581, 0.000,
             1.000, 2.032, 0.000, 0.000,
             0.000, 0.000, 0.000, 0.000
        };
    
    return mul(coeffs,yuv);
}

float4 main(float2 tex : TEXCOORD0) : COLOR
{
    float dx=1/width;
    float dy=1/height;
    
    float4 yuv00=rgb2yuv(getPixel(tex,-dx,-dy));
    float4 yuv01=rgb2yuv(getPixel(tex,-dx,  0));
    float4 yuv02=rgb2yuv(getPixel(tex,-dx, dy));
    float4 yuv10=rgb2yuv(getPixel(tex,  0,-dy));
    float4 yuv11=rgb2yuv(getPixel(tex,  0,  0));
    float4 yuv12=rgb2yuv(getPixel(tex,  0, dy));
    float4 yuv20=rgb2yuv(getPixel(tex, dx,-dy));
    float4 yuv21=rgb2yuv(getPixel(tex, dx,  0));
    float4 yuv22=rgb2yuv(getPixel(tex, dx, dy));

    float4 yuv=
        (yuv00*1+yuv01*2+yuv02*1+
         yuv10*2+yuv11*4+yuv12*2+
         yuv20*1+yuv21*2+yuv22*1)/16;
    
    yuv.r=yuv11.r;

    return yuv2rgb(yuv);
}