source: code/archive/skybox/Media/materials/programs/DepthShadowmap.hlsl

/* This file implements standard programs for depth shadow mapping. 
   These particular ones are suitable for additive lighting models, and
   include 3 techniques to reduce depth fighting on self-shadowed surfaces,
   constant bias, gradient (slope-scale) bias, and a fuzzy shadow map comparison*/


// Shadow caster vertex program.
void casterVP(
        float4 position                 : POSITION,
        out float4 outPos               : POSITION,
        out float2 outDepth             : TEXCOORD0,

        uniform float4x4 worldViewProj,
        uniform float4 texelOffsets,
        uniform float4 depthRange
        )
{
        outPos = mul(worldViewProj, position);

        // fix pixel / texel alignment
        outPos.xy += texelOffsets.zw * outPos.w;
        // linear depth storage
        // offset / scale range output
#if LINEAR_RANGE
        outDepth.x = (outPos.z - depthRange.x) * depthRange.w;
#else
        outDepth.x = outPos.z;
#endif
        outDepth.y = outPos.w;
}


// Shadow caster fragment program for high-precision single-channel textures    
void casterFP(
        float2 depth                    : TEXCOORD0,
        out float4 result               : COLOR)
        
{
#if LINEAR_RANGE
        float finalDepth = depth.x;
#else
        float finalDepth = depth.x / depth.y;
#endif
        // just smear across all components 
        // therefore this one needs high individual channel precision
        result = float4(finalDepth, finalDepth, finalDepth, 1);
}


        
void receiverVP(
        float4 position         : POSITION,
        float4 normal           : NORMAL,

        out float4 outPos                       : POSITION,
        out float4 outColour            : COLOR,
        out float4 outShadowUV          : TEXCOORD0,

        uniform float4x4 world,
        uniform float4x4 worldIT,
        uniform float4x4 worldViewProj,
        uniform float4x4 texViewProj,
        uniform float4 lightPosition,
        uniform float4 lightColour,
        uniform float4 shadowDepthRange
        )
{
        float4 worldPos = mul(world, position);
        outPos = mul(worldViewProj, position);

        float3 worldNorm = mul(worldIT, normal).xyz;

        // calculate lighting (simple vertex lighting)
        float3 lightDir = normalize(
                lightPosition.xyz -  (worldPos.xyz * lightPosition.w));

        outColour = lightColour * max(dot(lightDir, worldNorm), 0.0);

        // calculate shadow map coords
        outShadowUV = mul(texViewProj, worldPos);
#if LINEAR_RANGE
        // adjust by fixed depth bias, rescale into range
        outShadowUV.z = (outShadowUV.z - shadowDepthRange.x) * shadowDepthRange.w;
#endif
        


        
}

void receiverFP(
        float4 position                 : POSITION,
        float4 shadowUV                 : TEXCOORD0,
        float4 vertexColour             : COLOR,

        uniform sampler2D shadowMap : register(s0),
        uniform float inverseShadowmapSize,
        uniform float fixedDepthBias,
        uniform float gradientClamp,
        uniform float gradientScaleBias,
        uniform float shadowFuzzyWidth,
        
        out float4 result               : COLOR)
{
        // point on shadowmap
#if LINEAR_RANGE
        shadowUV.xy = shadowUV.xy / shadowUV.w;
#else
        shadowUV = shadowUV / shadowUV.w;
#endif
        float centerdepth = tex2D(shadowMap, shadowUV.xy).x;
    
    // gradient calculation
        float pixeloffset = inverseShadowmapSize;
    float4 depths = float4(
        tex2D(shadowMap, shadowUV.xy + float2(-pixeloffset, 0)).x,
        tex2D(shadowMap, shadowUV.xy + float2(+pixeloffset, 0)).x,
        tex2D(shadowMap, shadowUV.xy + float2(0, -pixeloffset)).x,
        tex2D(shadowMap, shadowUV.xy + float2(0, +pixeloffset)).x);

        float2 differences = abs( depths.yw - depths.xz );
        float gradient = min(gradientClamp, max(differences.x, differences.y));
        float gradientFactor = gradient * gradientScaleBias;

        // visibility function
        float depthAdjust = gradientFactor + (fixedDepthBias * centerdepth);
        float finalCenterDepth = centerdepth + depthAdjust;

        // shadowUV.z contains lightspace position of current object

#if FUZZY_TEST
        // fuzzy test - introduces some ghosting in result and doesn't appear to be needed?
        //float visibility = saturate(1 + delta_z / (gradient * shadowFuzzyWidth));
        float visibility = saturate(1 + (finalCenterDepth - shadowUV.z) * shadowFuzzyWidth * shadowUV.w);

        result = vertexColour * visibility;
#else
        // hard test
#if PCF
        // use depths from prev, calculate diff
        depths += depthAdjust.xxxx;
        float final = (finalCenterDepth > shadowUV.z) ? 1.0f : 0.0f;
        final += (depths.x > shadowUV.z) ? 1.0f : 0.0f;
        final += (depths.y > shadowUV.z) ? 1.0f : 0.0f;
        final += (depths.z > shadowUV.z) ? 1.0f : 0.0f;
        final += (depths.w > shadowUV.z) ? 1.0f : 0.0f;
        
        final *= 0.2f;

        result = float4(vertexColour.xyz * final, 1);
        
#else
        result = (finalCenterDepth > shadowUV.z) ? vertexColour : float4(0,0,0,1);
#endif

#endif
   

        
}




// Expand a range-compressed vector
float3 expand(float3 v)
{
        return (v - 0.5) * 2;
}


/* Normal mapping plus depth shadowmapping receiver programs
*/
void normalMapShadowReceiverVp(float4 position  : POSITION,
                         float3 normal          : NORMAL,
                         float2 uv                      : TEXCOORD0,
                         float3 tangent     : TANGENT0,
                         
                         // outputs
                         out float4 outPos       : POSITION,
                         out float4 outShadowUV  : TEXCOORD0,
                         out float2 oUv                  : TEXCOORD1,
                         out float3 oTSLightDir  : TEXCOORD2,
                         // parameters
                         uniform float4 lightPosition, // object space
                         uniform float4x4 world,
                         uniform float4x4 worldViewProj,
                         uniform float4x4 texViewProj)
{
        float4 worldPos = mul(world, position);
        outPos = mul(worldViewProj, position);

        // calculate shadow map coords
        outShadowUV = mul(texViewProj, worldPos);
#if LINEAR_RANGE
        // adjust by fixed depth bias, rescale into range
        outShadowUV.z = (outShadowUV.z - shadowDepthRange.x) * shadowDepthRange.w;
#endif
        
        // pass the main uvs straight through unchanged
        oUv = uv;

        // calculate tangent space light vector
        // Get object space light direction
        // Non-normalised since we'll do that in the fragment program anyway
        float3 lightDir = lightPosition.xyz -  (position * lightPosition.w);

        // Calculate the binormal (NB we assume both normal and tangent are
        // already normalised)
        // NB looks like nvidia cross params are BACKWARDS to what you'd expect
        // this equates to NxT, not TxN
        float3 binormal = cross(tangent, normal);
        
        // Form a rotation matrix out of the vectors
        float3x3 rotation = float3x3(tangent, binormal, normal);
        
        // Transform the light vector according to this matrix
        oTSLightDir = mul(rotation, lightDir);

        
}


void normalMapShadowReceiverFp(
                          float4 shadowUV       : TEXCOORD0,
                          float2 uv                     : TEXCOORD1,
                          float3 TSlightDir : TEXCOORD2,

                          out float4 result     : COLOR,

                          uniform float4 lightColour,
                          uniform float inverseShadowmapSize,
                          uniform float fixedDepthBias,
                          uniform float gradientClamp,
                          uniform float gradientScaleBias,
                          uniform float shadowFuzzyWidth,
                          
                          uniform sampler2D   shadowMap : register(s0),
                          uniform sampler2D   normalMap : register(s1),
                          uniform samplerCUBE normalCubeMap : register(s2))
{

        // retrieve normalised light vector, expand from range-compressed
        float3 lightVec = expand(texCUBE(normalCubeMap, TSlightDir).xyz);

        // get bump map vector, again expand from range-compressed
        float3 bumpVec = expand(tex2D(normalMap, uv).xyz);

        // Calculate dot product
        float4 vertexColour = lightColour * dot(bumpVec, lightVec);


        // point on shadowmap
#if LINEAR_RANGE
        shadowUV.xy = shadowUV.xy / shadowUV.w;
#else
        shadowUV = shadowUV / shadowUV.w;
#endif
        float centerdepth = tex2D(shadowMap, shadowUV.xy).x;
    
    // gradient calculation
        float pixeloffset = inverseShadowmapSize;
    float4 depths = float4(
        tex2D(shadowMap, shadowUV.xy + float2(-pixeloffset, 0)).x,
        tex2D(shadowMap, shadowUV.xy + float2(+pixeloffset, 0)).x,
        tex2D(shadowMap, shadowUV.xy + float2(0, -pixeloffset)).x,
        tex2D(shadowMap, shadowUV.xy + float2(0, +pixeloffset)).x);

        float2 differences = abs( depths.yw - depths.xz );
        float gradient = min(gradientClamp, max(differences.x, differences.y));
        float gradientFactor = gradient * gradientScaleBias;

        // visibility function
        float depthAdjust = gradientFactor + (fixedDepthBias * centerdepth);
        float finalCenterDepth = centerdepth + depthAdjust;

        // shadowUV.z contains lightspace position of current object

#if FUZZY_TEST
        // fuzzy test - introduces some ghosting in result and doesn't appear to be needed?
        //float visibility = saturate(1 + delta_z / (gradient * shadowFuzzyWidth));
        float visibility = saturate(1 + (finalCenterDepth - shadowUV.z) * shadowFuzzyWidth * shadowUV.w);

        result = vertexColour * visibility;
#else
        // hard test
#if PCF
        // use depths from prev, calculate diff
        depths += depthAdjust.xxxx;
        float final = (finalCenterDepth > shadowUV.z) ? 1.0f : 0.0f;
        final += (depths.x > shadowUV.z) ? 1.0f : 0.0f;
        final += (depths.y > shadowUV.z) ? 1.0f : 0.0f;
        final += (depths.z > shadowUV.z) ? 1.0f : 0.0f;
        final += (depths.w > shadowUV.z) ? 1.0f : 0.0f;
        
        final *= 0.2f;

        result = float4(vertexColour.xyz * final, 1);
        
#else
        result = (finalCenterDepth > shadowUV.z) ? vertexColour : float4(0,0,0,1);
#endif

#endif


        
}