#include "common.hlsli"

struct v2p
{
    float4 tc0 : TEXCOORD0; // Central
    float4 tc1 : TEXCOORD1; // -1,+1
    float4 tc2 : TEXCOORD2; // -2,+2
    float4 tc3 : TEXCOORD3; // -3,+3
    float4 tc4 : TEXCOORD4; // -4,+4
    float4 tc5 : TEXCOORD5; // -5,+5
    float4 tc6 : TEXCOORD6; // -6,+6
    float4 tc7 : TEXCOORD7; // -7,+7
};

#define LUMINANCE_BASE 0.0001f

float luminance(float2 tc)
{
    float3 source = tex2D(s_image, tc);
    return dot(source, LUMINANCE_VECTOR * def_hdr);
}

// 	perform 2x2=4s convolution, working on 4x4=16p area
//	that means 256x256 source will be scaled to (256/4)x(256/4) = 64x64p
//	a):	256x256 => 64x64p	with log
//	b):	64x64p	=> 8x8p
//	c):	8x8p	=> 1x1p		with exp
float4 main(v2p I) : COLOR
{
    // first 8 bilinear samples (8x4 = 32 pixels)
    float4 final;
    final.x = luminance(I.tc0);
    final.y = luminance(I.tc1);
    final.z = luminance(I.tc2);
    final.w = luminance(I.tc3);

    // OK
    return final;
}