source: GTP/trunk/App/Demos/Vis/FriendlyCulling/src/shaders/tonemap.cg @ 3214

#include "../shaderenv.h"


struct frag
{
         // normalized screen position
        float2 texCoord: TEXCOORD0; 

        float2 lt: TEXCOORD1; // left top
        float2 rb: TEXCOORD2; // right bottom
        float2 rt: TEXCOORD3; // right top
        float2 lb: TEXCOORD4; // left bottom
};


struct pixel
{
        float4 col: COLOR0;
};


/** Does the first downsampling step and on the same time calculates the 
        intensity.
*/
float4 GreyScaleDownSample(frag IN,
                                                   uniform sampler2D colors,
                                                   uniform float2 downSampleOffs[4]
                                                   ): COLOR
{

        // Compute the average of the 4 necessary samples
        float average = .0f;
        float maximum = .0f;

        // the rgb-to-luminance weightings
        const float3 w = float3(0.299f, 0.587f, 0.114f);
        //const float3 w = float3(0.2125f, 0.7154f, 0.0721f);

        float4 color;

        for (int i = 0; i < 4; ++ i)
        {
                color = tex2D(colors, downSampleOffs[i]);
                const float intensity = dot(cols[i].rgb, w);

                maximum = max(maximum, intensity);
                average += log(1e-5f + intensity);
        }

        average *= 0.25f;

        // Output the luminance to the render target
        return float4(average, maximum, 0.0f, 1.0f);
}
    

/** Used for downsampling the tone map parameters (average loglum, maximum)
        to the next lower level. This has to be applied until there is only
        a 1x1 texture which holds the required numbers.
*/
float4 DownSampleForToneMapping(frag IN,
                                                                uniform sampler2D colors,
                                                                uniform float2 downSampleOffs[4]): COLOR
{    
        float average = .0f;
        float maximum = .0f;
        
        float4 color;

        for (int i = 0; i < 4; ++ i)
        {
                color = tex2D(colors, downSampleOffs[i]);

                maximum = max(maximum, color.y);
                average += color.x;
        }

        average *= 1.0f / (float)NUM_DOWNSAMPLES;

        return float4(average, maximum, 0.0f, 1.0f);
}



pixel ToneMap(frag IN,
                          uniform sampler2D colors,
                          uniform float imageKey, 
                          uniform float whiteLum, 
                          uniform float middleGrey)
{
        pixel OUT;
        
        float4 color = tex2D(colors, IN.texCoord);

        const float pixLum = 0.2125f * color.x + 0.7154f * color.y + 0.0721f * color.z;
        
        // obtain new image key from highest mipmap level
        float logLumScaled = tex2Dlod(colors, float4(.5f, .5f, 0, MAX_LOD_LEVEL)).w;
        float logLum = logLumScaled * LOGLUM_RANGE + MINLOGLUM;

        float newImageKey = max(exp(logLum), 1e-3f);

        // adjust to middle gray
        const float lum = middleGrey * pixLum / newImageKey;
        // map to range and calc burnout
        const float scaleLum = lum * (1.0f + lum / whiteLum * whiteLum) / (1.0f + lum);

        OUT.col = color * scaleLum / pixLum;
        OUT.col.w = color.w;

        return OUT;
}


pixel CalcAvgLogLum(frag IN, uniform sampler2D colors)
{
        ////////////
        //-- write out logaritmic luminance for tone mapping

        pixel OUT;

        const float4 color = tex2Dlod(colors, float4(IN.texCoord.xy, 0, 0));
        OUT.col = color;

        // the old loglum is stored in the hightest mipmap-level
        float oldLogLum = tex2Dlod(colors, float4(IN.texCoord.xy, 0, MAX_LOD_LEVEL)).w;

        // the intensity weights
        const float3 w = float3(0.299f, 0.587f, 0.114f);

        float lum = dot(color.rgb, w);
        float logLum = log(max(1e-3f, lum));

        float logLumOffset = MINLOGLUM * INV_LOGLUM_RANGE;
        float logLumScaled = logLum * INV_LOGLUM_RANGE - logLumOffset;


        /////////////
        //-- exponential smoothing of the tone mapping over time

        if (oldLogLum > 1e-3f) // check if loglum from last frame too small (=> tm too bright)
                OUT.col.w = lerp(oldLogLum, logLumScaled, TONE_MAPPING_EXPONENTIAL_FACTOR);
        else
                OUT.col.w = logLumScaled;

        return OUT;
}