source: code/archive/skybox/Media/materials/programs/hdr.hlsl @ 10980

// RGBE mode utilities
// RGB each carry a mantissa, A carries a shared exponent
// The exponent is calculated based on the largest colour channel


float3 decodeRGBE8(in float4 rgbe)
{
    // get exponent (-128 since it can be +ve or -ve)
        float exp = rgbe.a * 255 - 128;
        
        // expand out the rgb value
        return rgbe.rgb * exp2(exp);
}

float4 encodeRGBE8(in float3 rgb)
{
        float4 ret;

    // What is the largest colour channel?
        float highVal = max(rgb.r, max(rgb.g, rgb.b));
        
        // Take the logarithm, clamp it to a whole value
        float exp = ceil(log2(highVal));

    // Divide the components by the shared exponent
        ret.rgb = rgb / exp2(exp);
        
        // Store the shared exponent in the alpha channel
        ret.a = (exp + 128) / 255;

        return ret;
}


static const float4 LUMINENCE_FACTOR  = float4(0.27f, 0.67f, 0.06f, 0.0f);
static const float MIDDLE_GREY = 0.72f;
static const float FUDGE = 0.001f;
static const float L_WHITE = 1.5f;
static const float4 BRIGHT_LIMITER = float4(0.6f, 0.6f, 0.6f, 0.0f);


/** Tone mapping function 
@note Only affects rgb, not a
@param inColour The HDR colour
@param lum The scene lumninence 
@returns Tone mapped colour
*/
float4 toneMap(float4 inColour, float lum)
{
        // From Reinhard et al
        // "Photographic Tone Reproduction for Digital Images"
        
        // Initial luminence scaling (equation 2)
    inColour.rgb *= MIDDLE_GREY / (FUDGE + lum);

        // Control white out (equation 4 nom)
    inColour.rgb *= (1.0f + inColour / L_WHITE);

        // Final mapping (equation 4 denom)
        inColour.rgb /= (1.0f + inColour);
        
        return inColour;

}

/* Downsample a 2x2 area and convert to greyscale
*/
float4 downscale2x2Luminence(
        float2 uv : TEXCOORD0,
        uniform float2 texelSize, // depends on size of source texture
        uniform sampler2D inRTT : register(s0)
    ) : COLOR
{
        
    float4 accum = float4(0.0f, 0.0f, 0.0f, 0.0f);

        float2 texOffset[4] = {
                -0.5, -0.5,
                -0.5,  0.5, 
                 0.5, -0.5,
                 0.5, 0.5 };

        for( int i = 0; i < 4; i++ )
    {
        // Get colour from source
        accum += tex2D(inRTT, uv + texelSize * texOffset[i]);
    }
    
        // Adjust the accumulated amount by lum factor
        // Cannot use float3's here because it generates dependent texture errors because of swizzle
        float lum = dot(accum, LUMINENCE_FACTOR);
        // take average of 4 samples
        lum *= 0.25;
        return lum;

}

/* Downsample a 3x3 area 
 * This shader is used multiple times on different source sizes, so texel size has to be configurable
*/
float4 downscale3x3(
        float2 uv : TEXCOORD0,
        uniform float2 texelSize, // depends on size of source texture
        uniform sampler2D inRTT : register(s0)
    ) : COLOR
{
        
    float4 accum = float4(0.0f, 0.0f, 0.0f, 0.0f);

        float2 texOffset[9] = {
                -1.0, -1.0,
                 0.0, -1.0,
                 1.0, -1.0,
                -1.0,  0.0,
                 0.0,  0.0,
                 1.0,  0.0,
                -1.0,  1.0,
                 0.0,  1.0,
                 1.0,  1.0
        };

        for( int i = 0; i < 9; i++ )
    {
        // Get colour from source
        accum += tex2D(inRTT, uv + texelSize * texOffset[i]);
    }
    
        // take average of 9 samples
        accum *= 0.1111111111111111;
        return accum;

}

/* Downsample a 3x3 area from main RTT and perform a brightness pass
*/
float4 downscale3x3brightpass(
        float2 uv : TEXCOORD0,
        uniform float2 texelSize, // depends on size of source texture
        uniform sampler2D inRTT : register(s0),
        uniform sampler2D inLum : register(s1)
    ) : COLOR
{
        
    float4 accum = float4(0.0f, 0.0f, 0.0f, 0.0f);

        float2 texOffset[9] = {
                -1.0, -1.0,
                 0.0, -1.0,
                 1.0, -1.0,
                -1.0,  0.0,
                 0.0,  0.0,
                 1.0,  0.0,
                -1.0,  1.0,
                 0.0,  1.0,
                 1.0,  1.0
        };

        for( int i = 0; i < 9; i++ )
    {
        // Get colour from source
        accum += tex2D(inRTT, uv + texelSize * texOffset[i]);
    }
    
        // take average of 9 samples
        accum *= 0.1111111111111111;

    // Reduce bright and clamp
    accum = max(float4(0.0f, 0.0f, 0.0f, 1.0f), accum - BRIGHT_LIMITER);

        // Sample the luminence texture
        float4 lum = tex2D(inLum, float2(0.5f, 0.5f));
        
        // Tone map result
        return toneMap(accum, lum.r);

}

/* Gaussian bloom, requires offsets and weights to be provided externally
*/
float4 bloom(
                float2 uv : TEXCOORD0,
                uniform float2 sampleOffsets[15],
                uniform float4 sampleWeights[15],       
                uniform sampler2D inRTT : register(s0)
                ) : COLOR
{
    float4 accum = float4(0.0f, 0.0f, 0.0f, 1.0f);
        float2 sampleUV;
    
    for( int i = 0; i < 15; i++ )
    {
        // Sample from adjacent points, 7 each side and central
        sampleUV = uv + sampleOffsets[i];
        accum += sampleWeights[i] * tex2D(inRTT, sampleUV);
    }
    
    return accum;
        
}
                

/* Final scene composition, with tone mapping
*/
float4 finalToneMapping(
        float2 uv : TEXCOORD0,
        uniform sampler2D inRTT : register(s0),
        uniform sampler2D inBloom : register(s1),
        uniform sampler2D inLum : register(s2)
    ) : COLOR
{
        // Get main scene colour
    float4 sceneCol = tex2D(inRTT, uv);

        // Get luminence value
        float4 lum = tex2D(inLum, float2(0.5f, 0.5f));

        // tone map this
        float4 toneMappedSceneCol = toneMap(sceneCol, lum.r);
        
        // Get bloom colour
    float4 bloom = tex2D(inBloom, uv);

        // Add scene & bloom
        return float4(toneMappedSceneCol.rgb + bloom.rgb, 1.0f);
        
}