source: GTP/trunk/App/Demos/Vis/FriendlyCulling/src/shaders/ssao.cg @ 3372

#include "../shaderenv.h"
#include "common.h"

////////////////////
// Screen Spaced Ambient Occlusion shader
// based on shader of Alexander Kusternig


#define USE_EYESPACE_DEPTH 1


struct fragment
{
        float2 texCoord: TEXCOORD0; 
        float3 view: TEXCOORD1;
};


struct pixel2
{
        float4 illum_col: COLOR0;
};


// this function is inspired from the paper of shamulgaan in order
// to get a physical expression for the occlusion culling
inline float occlusionPower(float radius, float dist)
{
        return 6.283185307179586476925286766559f * (1.0f - cos(asin(radius / dist)));
}



// reconstruct world space position
inline float3 ReconstructSamplePos(float eyeSpaceDepth,
                                                                   float2 texcoord, 
                                                                   float3 bl, float3 br, float3 tl, float3 tr)
{
        float3 viewVec = Interpol(texcoord, bl, br, tl, tr);
        float3 samplePos = -viewVec * eyeSpaceDepth;

        return samplePos;
}


float ComputeConvergence(uniform sampler2D tex, float2 texCoord, float2 res)
{
        // get the minimum convergence by exactly sampling the 4 surrounding
        // texels in the old texture, otherwise flickering because convergence
        // will be interpolated when upsampling and filter size does not match!

        const float2 invRes = float2(1.0f / res.x, 1.0f / res.y);

        // get position exactly between texel centers
        float2 center = (floor(texCoord * res) + float2(.5f)) * invRes;
        
        //const float convergence = tex2Dlod(tex, float4(center, 0, 0)).y;
        const float convergence = tex2Dlod(tex, float4(texCoord, 0, 0)).y;

        return convergence;
}

/** This shader computes the reprojection and stores 
        the ssao value of the old pixel as well as the
        weight of the pixel in the new frame.
*/
inline float3 Reproject(float4 worldPos,
                                                float eyeSpaceDepth,
                                                float2 texcoord0,
                                                float3 oldEyePos,
                                                sampler2D oldTex,
                                                float4x4 oldModelViewProj,
                                                sampler2D colors,
                                                float3 projPos,
                                                float invW,
                                                float3 oldbl,
                                                float3 oldbr,
                                                float3 oldtl,
                                                float3 oldtr,
                                                float3 diffVec
                                                )
{
        // compute position from old frame for dynamic objects + translational portion
        const float3 translatedPos = diffVec - oldEyePos + worldPos.xyz;


        /////////////////
        //-- reproject into old frame and calculate texture position of sample in old frame

        // note: the old model view matrix only holds the view orientation part
        float4 backProjPos = mul(oldModelViewProj, float4(translatedPos, 1.0f));
        backProjPos /= backProjPos.w;
        
        // fit from unit cube into 0 .. 1
        const float2 oldTexCoords = backProjPos.xy * 0.5f + 0.5f;
        // retrieve the sample from the last frame
        const float4 oldPixel = tex2Dlod(oldTex, float4(oldTexCoords, .0f, .0f));

        // the ssao value in the old frame
        const float ssao = oldPixel.x;

        // calculate eye space position of sample in old frame
        const float oldEyeSpaceDepth = oldPixel.w;

        // vector from eye pos to old sample 
        const float3 viewVec = Interpol(oldTexCoords, oldbl, oldbr, oldtl, oldtr);
        const float invLen = 1.0f / length(viewVec);
        const float projectedEyeSpaceDepth = invLen * length(translatedPos);
        //const float projectedEyeSpaceDepth = length(translatedPos);
        
        const float depthDif = abs(1.0f - oldEyeSpaceDepth / projectedEyeSpaceDepth);

        // the weight of the accumulated samples from the previous frames
        float w;
        float idx;


        //////////////
        //-- reuse old value only if it was still valid in the old frame

        if (1
                && (oldTexCoords.x > .0f) && (oldTexCoords.x < 1.0f)
                && (oldTexCoords.y > .0f) && (oldTexCoords.y < 1.0f)
                && (depthDif <= MIN_DEPTH_DIFF) 
                )
        {
#if 0
                idx = floor(oldPixel.z);
#else

                // nearest neighbour
                float2 center;
                center.x = (floor(oldTexCoords.x * 1024) + .5f) / 1024;
                center.y = (floor(oldTexCoords.y * 768) + .5f) / 768;
                
                const float4 oldPixelExact = tex2Dlod(oldTex, float4(center, .0f, .0f)); 
                idx = oldPixelExact.z;
#endif

                w = oldPixel.y;
        }
        else
        {       
                w   = .0f;
                idx = .0f;
        }

        return float3(ssao, w, idx);
}


/** The ssao shader returning the an intensity value between 0 and 1.
        This version of the ssao shader uses the dotproduct between 
        pixel-to-sample direction and sample normal as weight.

    The algorithm works like the following:
        1) Check in a circular area around the current position.
        2) Shoot vectors to the positions there, and check the angle to these positions.
        3) Summing up these angles gives an estimation of the occlusion at the current position.
*/
float3 ssao2(fragment IN,
                         sampler2D colors,
                         sampler2D noiseTex,
                         sampler2D samples,
                         float3 normal,
                         float3 centerPosition,
                         float radius,
                         float3 bl,
                         float3 br,
                         float3 tl,
                         float3 tr, 
                         float3 viewDir,
                         float convergence,
                         float sampleIntensity,
                         bool isMovingObject,
                         sampler2D normalTex,
                         float idx
                         )
{
        float total_ao = .0f;
        float validSamples = .0f;
        float numSamples = .0f;

        for (int i = 0; i < NUM_SAMPLES; ++ i) 
        {
                float2 offset;

                const float2 ssaoOffset = 
                        tex2Dlod(samples, float4((0.5f + i + idx) / NUM_PRECOMPUTED_SAMPLES, 0.5f, .0f, .0f)).xy;

                ////////////////////
                //-- add random noise: reflect around random normal vector 
                //-- (affects performance for some reason!)

                if (!USE_OPTIMIZATION ||
                        (convergence < SSAO_CONVERGENCE_THRESHOLD))
                {
                        float2 mynoise = tex2Dlod(noiseTex, float4(IN.texCoord * 4.0f, 0, 0)).xy;
                        //offset = myreflect(samples[i], mynoise);
                        //offset = myrotate(samples[i], mynoise.x);
                        offset = myrotate(ssaoOffset, mynoise.x);
                }
                else
                {
                        offset = ssaoOffset;
                }
                
                // weight with projected coordinate to reach similar kernel size for near and far
                const float2 texcoord = IN.texCoord.xy + offset * radius;

                const float4 sampleColor = tex2Dlod(colors, float4(texcoord, .0f, .0f));
                const float3 samplePos = ReconstructSamplePos(sampleColor.w, texcoord, bl, br, tl, tr);
                

                ////////////////
                //-- compute contribution of sample using the direction and angle

                float3 dirSample = samplePos - centerPosition;

                const float minDist = 1e-6f;
                const float delta = 1e-3f;

                const float lengthToSample = length(dirSample);
                const float sampleWeight = 1.0f / (lengthToSample + delta);

                dirSample /= max(lengthToSample, minDist); // normalize


                // angle between current normal and direction to sample controls AO intensity.
                const float cosAngle = dot(dirSample, normal);

                // the normal of the current sample
                const float3 sampleNormal = normalize(tex2Dlod(normalTex, float4(texcoord, 0, 0)).xyz);
                
                // angle between current normal and direction to sample controls AO intensity.
                //const float cosAngle2 = dot(-dirSample, sampleNormal);
                const float cosAngle2 = .5f + dot(sampleNormal, -normal) * .5f;

                dirSample *= minDist;
                const float aoContrib = sampleIntensity * sampleWeight;

                //const float aoContrib = (1.0f > lengthToSample) ? occlusionPower(9e-2f, DISTANCE_SCALE + lengthToSample): .0f;
                //total_ao += max(cosAngle, .0f) * max(cosAngle2, .0f) * aoContrib;
                total_ao += max(cosAngle, .0f) * cosAngle2 * aoContrib;

                ++ numSamples;

                // check if the samples have been valid in the last frame
                // only mark sample as invalid if in the last / current frame
                // they possibly have any influence on the ao

                const float changeFactor = sampleColor.y;
                const float pixelValid = sampleColor.x;

                // hack:
                // we check if the sample could have been near enough 
                // to the current pixel or if the angle is small enough
                // to have any influence in the current or last frame
#if 1
                const float tooFarAway = step(0.5f, lengthToSample - changeFactor);
                const float partlyResetThres = 1.0f;

                if (pixelValid <= partlyResetThres)
                        validSamples = max(validSamples, pixelValid * (1.0f - tooFarAway) * step(-0.1f, cosAngle));
                else
                        validSamples = max(validSamples, pixelValid);
#endif

#ifdef USE_GTX
                // we can bail out early and use a minimal #samples)
                // if some conditions are met as long as the hardware supports it
                if (numSamples >= MIN_SAMPLES)
                {
                        //break;
                        // if the pixel belongs to a static object and all the samples stay valid in the current frame
                        if (!isMovingObject && (validSamples < 1.0f) && (convergence > NUM_SAMPLES)) break;
                        // if the pixel belongs to a dynamic object but the #accumulated samples for this pixel is sufficiently high 
                        // (=> there was no discontinuity recently)
                        //else if (isMovingObject && (convergence > SSAO_CONVERGENCE_THRESHOLD)) break;
                        else if (isMovingObject && (convergence > NUM_SAMPLES * 5)) break;
                }
#endif
        }

        // "normalize" ao contribution
        total_ao /= numSamples;

#if 1
        // if surface normal perpenticular to view dir, approx. half of the samples will not count
        // => compensate for this (on the other hand, projected sampling area could be larger!)
        const float viewCorrection = 1.0f + VIEW_CORRECTION_SCALE * max(dot(viewDir, normal), 0.0f);
        total_ao *= viewCorrection;
#endif

        //return float3(total_ao, validSamples, numSamples);
        return float3(min(1.0f, total_ao), validSamples, numSamples);
}

//#define TRYOUT

#ifdef TRYOUT

/** The ssao shader returning the an intensity value between 0 and 1.
        This version of the ssao shader uses the dotproduct between 
        pixel-to-sample direction and sample normal as weight.

    The algorithm works like the following:
        1) Check in a circular area around the current position.
        2) Shoot vectors to the positions there, and check the angle to these positions.
        3) Summing up these angles gives an estimation of the occlusion at the current position.
*/
float3 ssao(fragment IN,
                        sampler2D colors,
                        sampler2D noiseTex,
                        sampler2D samples,
                        float3 normal,
                        float3 centerPosition,
                        float radius,
                        float3 bl,
                        float3 br,
                        float3 tl,
                        float3 tr, 
                        float3 viewDir,
                        float convergence,
                        float sampleIntensity,
                        bool isMovingObject,
                        float oldIdx
                        )
{
        float total_ao = .0f;
        float validSamples = .0f;
        float numSamples = .0f;

        for (int i = 0; i < NUM_SAMPLES; ++ i) 
        {
                float2 offset;

                const float2 ssaoOffset = 
                        tex2Dlod(samples, float4((0.5f + i + oldIdx) / NUM_PRECOMPUTED_SAMPLES, 0.5f, .0f, .0f)).xy;


                ////////////////////
                //-- add random noise: reflect around random normal vector 
                //-- (affects performance for some reason!)

                if (!USE_OPTIMIZATION ||
                        (convergence < SSAO_CONVERGENCE_THRESHOLD))
                {
                        float2 mynoise = tex2Dlod(noiseTex, float4(IN.texCoord * 4.0f, 0, 0)).xy;
                        //offset = myrotate(samples[i], mynoise.x);
                        offset = myrotate(ssaoOffset, mynoise.x);
                }
                else
                {
                        offset = ssaoOffset;
                }


                // weight with projected coordinate to reach similar kernel size for near and far
                const float2 texcoord = IN.texCoord.xy + offset * radius;

                const float4 sampleColor = tex2Dlod(colors, float4(texcoord, .0f, .0f));
                const float3 samplePos = ReconstructSamplePos(sampleColor.w, texcoord, bl, br, tl, tr);
                

                ////////////////
                //-- compute contribution of sample using the direction and angle

                float3 dirSample = samplePos - centerPosition;

                const float minDist = 1e-6f;
                const float eps = 1e-3f;

                const float lengthToSample = length(dirSample);
                const float sampleWeight = 1.0f / max(lengthToSample, eps);

                dirSample /= max(length(dirSample), minDist); // normalize

                // angle between current normal and direction to sample controls AO intensity.
                const float cosAngle = dot(dirSample, normal);

                //const float aoContrib = sampleIntensity / sqrLen;
                const float aoContrib = sampleIntensity * sampleWeight;
                //const float aoContrib = (1.0f > lengthToSample) ? occlusionPower(9e-2f, DISTANCE_SCALE + lengthToSample): .0f;

                total_ao += max(cosAngle, .0f) * aoContrib;

                ++ numSamples;

#ifdef PERFORMANCE_TEST
                // check if the samples have been valid in the last frame
                // only mark sample as invalid if in the last / current frame
                // they possibly have any influence on the AO

                const float changeFactor = sampleColor.y;
                const float pixelValid = sampleColor.x;

                // hack:
                // we check if the sample could have been near enough to the current pixel 
                // or if the angle is small enough
                // to have any influence in the current or last frame

#if 1
                const float partlyResetThres = 1.0f;

                const float tooFarAway = step(.5f, lengthToSample - changeFactor);
                if (0)//pixelValid <= partlyResetThres)
                        validSamples = max(validSamples, pixelValid * (1.0f - tooFarAway) * step(-.1f, cosAngle));
                else
                        validSamples = max(validSamples, pixelValid);
#endif

#ifdef USE_GTX
                // we can bail out early and use a minimal #samples)
                // if some conditions are met as long as the hardware supports it
                if (numSamples >= MIN_SAMPLES)
                {
                        //break;
                        // if the pixel belongs to a static object and all the samples stay valid in the current frame
                        if (!isMovingObject && (validSamples < 1.0f) && (convergence > NUM_SAMPLES)) break;
                        // if the pixel belongs to a dynamic object but the #accumulated samples for this pixel is sufficiently high 
                        // (=> there was no discontinuity recently)
                        //else if (isMovingObject && (convergence > SSAO_CONVERGENCE_THRESHOLD)) break;
                        else if (isMovingObject && (convergence > NUM_SAMPLES * 5)) break;
                }
#endif

#endif // PERFORMANCE_TEST
        }

        // "normalize" ao contribution
        total_ao /= numSamples;

#if 1
        // if surface normal perpenticular to view dir, approx. half of the samples will not count
        // => compensate for this (on the other hand, projected sampling area could be larger!)
        const float viewCorrection = 1.0f + VIEW_CORRECTION_SCALE * max(dot(viewDir, normal), 0.0f);
        total_ao *= viewCorrection;
#endif

        //return float3(total_ao, validSamples, numSamples);
        return float3(min(1.0f, total_ao), validSamples, numSamples);
}

#else

float3 ssao(fragment IN,
                        sampler2D colors,
                        sampler2D noiseTex,
                        float2 dummySamples[NUM_SAMPLES],
                        sampler2D samples,
                        float3 normal,
                        float3 centerPosition,
                        float radius,
                        float3 bl,
                        float3 br,
                        float3 tl,
                        float3 tr, 
                        float3 viewDir,
                        float convergence,
                        float sampleIntensity,
                        bool isMovingObject,
                        float oldIdx,
                        sampler2D attribsTex,
                        float3 oldPos
                        )
{
        float total_ao = .0f;
        float validSamples = .0f;
        float numSamples = .0f;

        //float3 diffVec = tex2Dlod(attribsTex, float4(IN.texCoord, 0, 0)).xyz;

        for (int i = 0; i < NUM_SAMPLES; ++ i) 
        {
                float2 offset;

                const float2 ssaoOffset = tex2Dlod(samples, float4((.5f + i + floor(oldIdx)) / NUM_PRECOMPUTED_SAMPLES, .5f, .0f, .0f)).xy;
                //const float2 ssaoOffset = dummySamples[i];

                ////////////////////
                //-- add random noise: reflect around random normal vector 
                //-- (affects performance for some reason!)

                if (!USE_OPTIMIZATION ||
                        (convergence < SSAO_CONVERGENCE_THRESHOLD))
                {
                        float2 mynoise = tex2Dlod(noiseTex, float4(IN.texCoord * 4.0f, 0, 0)).xy;
                        //offset = myreflect(samples[i], mynoise); offset = myrotate(samples[i], mynoise.x);
                        offset = myrotate(ssaoOffset, mynoise.x);
                }
                else
                {
                        offset = ssaoOffset;
                }


                // weight with projected coordinate to reach similar kernel size for near and far
                const float2 texcoord = IN.texCoord.xy + offset * radius;

                const float4 sampleColor = tex2Dlod(colors, float4(texcoord, .0f, .0f));
                const float3 oldSamplePos = sampleColor.xyz;
                const float3 samplePos = ReconstructSamplePos(sampleColor.w, texcoord, bl, br, tl, tr);
                
                

                ////////////////
                //-- compute contribution of sample using the direction and angle

                float3 dirSample = samplePos - centerPosition;

                const float eps = 1e-3f;

                const float lengthToSample = length(dirSample);
                const float sampleWeight = 1.0f / max(lengthToSample, eps);

                dirSample /= max(length(dirSample), eps); // normalize

                // angle between current normal and direction to sample controls AO intensity.
                const float cosAngle = dot(dirSample, normal);

                //const float aoContrib = sampleIntensity / sqrLen;
                const float aoContrib = sampleIntensity * sampleWeight;
                //const float aoContrib = (1.0f > lengthToSample) ? occlusionPower(9e-2f, DISTANCE_SCALE + lengthToSample): .0f;

                total_ao += max(cosAngle, .0f) * aoContrib;
                ++ numSamples;


#ifdef PERFORMANCE_TEST
                // check if the samples have been valid in the last frame
                // only mark sample as invalid if in the last / current frame
                // they possibly have any influence on the ao

                const float3 oldVector = oldSamplePos - oldPos;
                const float oldDistance = length(oldVector);
                //const float cosAngle2 = dot(oldVector, normal);
                
                const float distanceDiff = abs(oldDistance - lengthToSample);

                float pixelValid = .0f;

                if ((texcoord.x > .0f) && (texcoord.x < 1.0f) && (texcoord.y > .0f) && (texcoord.y < 1.0f))
                {
                        if ((oldSamplePos.x > 1e14f))// || ((cosAngle >= 0) && (distanceDiff > 1e-3f)))
                        {
                                pixelValid = 100.0f;
                        }
                        else if ((cosAngle >= 0) && (distanceDiff > 1e-3f))
                        {
                                pixelValid = 5.0f;
                        }
                }

                validSamples = max(validSamples, pixelValid);

#ifdef USE_GTX
                // we can bail out early and use a minimal #samples)
                // if some conditions are met as long as the hardware supports it
                if (numSamples >= MIN_SAMPLES)
                {
                        //break;
                        // if the pixel belongs to a static object and all the samples stay valid in the current frame
                        if (!isMovingObject && (validSamples < 1.0f) && (convergence > NUM_SAMPLES)) break;
                        // if the pixel belongs to a dynamic object but the #accumulated samples for this pixel is sufficiently high 
                        // (=> there was no discontinuity recently)
                        //else if (isMovingObject && (convergence > SSAO_CONVERGENCE_THRESHOLD)) break;
                        else if (isMovingObject && (convergence > NUM_SAMPLES * 5)) break;
                }
#endif

#endif // PERFORMANCE_TEST
        }

        // "normalize" ao contribution
        total_ao /= numSamples;

#if 1
        // if surface normal perpenticular to view dir, approx. half of the samples will not count
        // => compensate for this (on the other hand, projected sampling area could be larger!)
        const float viewCorrection = 1.0f + VIEW_CORRECTION_SCALE * max(dot(viewDir, normal), 0.0f);
        total_ao *= viewCorrection;
#endif

        //return float3(total_ao, validSamples, numSamples);
        return float3(min(1.0f, total_ao), validSamples, numSamples);
}
#endif


/** The mrt shader for screen space ambient occlusion
*/
pixel2 main(fragment IN, 
                        uniform sampler2D colors,
                        uniform sampler2D normals,
                        uniform sampler2D noiseTex,
                        uniform sampler2D samples,
                        uniform float2 dummySamples[NUM_SAMPLES],
                        uniform sampler2D oldTex,
                        uniform float4x4 modelViewProj,
                        uniform float4x4 oldModelViewProj,
                        uniform float temporalCoherence,
                        uniform float3 bl,
                        uniform float3 br,
                        uniform float3 tl,
                        uniform float3 tr,
                        uniform float3 oldEyePos,
                        uniform float3 oldbl,
                        uniform float3 oldbr,
                        uniform float3 oldtl,
                        uniform float3 oldtr,
                        uniform sampler2D attribsTex,
                        uniform float kernelRadius,
                        uniform float sampleIntensity
                        ,uniform float dummyIdx
                        )
{
        pixel2 OUT;

        //const float3 normal = normalize(tex2Dlod(normals, float4(IN.texCoord, 0 ,0)).xyz);
        const float3 normal = tex2Dlod(normals, float4(IN.texCoord, 0 ,0)).xyz;

        // reconstruct position from the eye space depth
        const float3 viewDir = IN.view;
        const float4 mycolor = tex2Dlod(colors, float4(IN.texCoord, 0, 0));
        const float eyeSpaceDepth = mycolor.w;
        const float4 eyeSpacePos = float4(-viewDir * eyeSpaceDepth, 1.0f);


        ////////////////
        //-- calculcate the current projected posiion (also used for next frame)
        
        float4 projPos = mul(modelViewProj, eyeSpacePos);
        const float invw = 1.0f / projPos.w;
        projPos *= invw;
        
        //const float radiusMult = kernelRadius;
        //const float radiusMult = 3e-2;
        const float radiusMult = kernelRadius * invw;
        
#ifdef PERFORMANCE_TEST 

        float3 diffVec = tex2Dlod(attribsTex, float4(IN.texCoord, 0, 0)).xyz;

        const float sqrMoveSpeed = SqrLen(diffVec);
        const bool isMovingObject = (sqrMoveSpeed > DYNAMIC_OBJECTS_THRESHOLD);

        
        /////////////////
        //-- compute temporal reprojection

        float3 temporalVals = Reproject(eyeSpacePos, eyeSpaceDepth, IN.texCoord, oldEyePos,
                                        oldTex, oldModelViewProj, 
                                                                        colors, 
                                                                        projPos.xyz, 
                                                                        invw, 
                                                                        oldbl, oldbr, oldtl, oldtr,
                                                                        diffVec
                                                                        );
        
        const float oldSsao = temporalVals.x;
        
        float oldWeight = temporalVals.y;
        float oldIdx = temporalCoherence > 1 ? temporalVals.z : 0;
        //float oldIdx = temporalVals.z;
        
#else

        const float3 diffVec      = float3(.0f);
        const bool isMovingObject = false;
        const float oldSsao       = .0f;
        
        float oldWeight = .0f;
        float oldIdx    = .0f;
        
#endif

        float3 ao;
        //$$temp matt
        //oldIdx = dummyIdx;

        // cull background note: this should be done with the stencil buffer
        if (eyeSpaceDepth < DEPTH_THRESHOLD)
        {
#ifdef TRYOUT
                ao = ssao(IN, colors, noiseTex, samples, normal, eyeSpacePos.xyz, 
                              radiusMult, bl, br, tl, tr, normalize(viewDir),
                              oldWeight, sampleIntensity, isMovingObject, oldIdx);
#else

                ao = ssao(IN, colors, noiseTex, dummySamples, samples,
                              normal, eyeSpacePos.xyz, radiusMult, bl, 
                              br, tl, tr, normalize(viewDir), 
                              oldWeight, sampleIntensity, isMovingObject, oldIdx,
                              attribsTex, mycolor.xyz);
#endif                            
        }
        else
        {
                 ao = float3(1.0f);
        }


#ifdef PERFORMANCE_TEST

        ///////////
        //-- check if we have to reset pixel because one of the sample points was invalid
        //-- only do this if the current pixel does not belong to a moving object

        // the weight equals the number of sampled shot in this pass
        const float newWeight = ao.z;
        // completely reset the ao in this pixel
        const float completelyResetThres = 20.0f;
        // don't fully reset the ao in this pixel, but give low weight to old solution
        const float partlyResetThres = 1.0f;
        
        // the new index for the next frame
        float newIdx;
        // the new weight for the next frame
        float combinedWeight;

        // don't check for moving objects, otherwise almost no coherence
        if (ao.y > completelyResetThres) 
        {
                oldWeight = newIdx = .0f;
        }
        else
        {
                newIdx = oldIdx + newWeight;
        }

        if (ao.y > partlyResetThres)
        {
                const float factor = 3.0f;

                oldWeight = min(oldWeight, factor * NUM_SAMPLES);

                if (newIdx >= factor * NUM_SAMPLES) 
                {
                        newIdx = .0f; 
                        //oldWeight = .0f;
                }

                //combinedWeight = oldWeight;
        }

        // the new weight for the next frame
        combinedWeight = clamp(newWeight + oldWeight, .0f, temporalCoherence);


        //////////
        //-- blend ao between old and new samples (and avoid division by zero)

        OUT.illum_col.x = ao.x * newWeight + oldSsao * oldWeight;
        OUT.illum_col.x /= (newWeight + oldWeight);

        OUT.illum_col.y = combinedWeight;
        OUT.illum_col.z = newIdx; // the new index
        OUT.illum_col.w = eyeSpaceDepth;

#else

        OUT.illum_col.x = ao.x;
        OUT.illum_col.w = eyeSpaceDepth;
        
#endif

        return OUT;
}