source: GTP/trunk/App/Demos/Vis/FriendlyCulling/src/shaders/ssao.cg @ 2868

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

//#define NUM_SAMPLES 8
#define NUM_SAMPLES 16

// rule of thumb: approx 1 / NUM_SAMPLES
#define SAMPLE_INTENSITY 0.15
//#define SAMPLE_INTENSITY 0.125f

#define AREA_SIZE 9e-1f
//#define VIEW_CORRECTION_SCALE 0.3f
#define VIEW_CORRECTION_SCALE 0.5f
#define DISTANCE_SCALE 1e-6f


struct fragment
{
         // normalized screen position
        float4 pos: WPOS;
        float4 texCoord: TEXCOORD0; 
        float3 view: COLOR0;
};


struct pixel
{
        float4 color: COLOR0;
};


float2 reflect(float2 pt, float2 n)
{
  // distance to plane
  float d = dot(n, pt);
  // reflect around plane
  float2 rpt = pt - d * 2.0f * n;

  return rpt;
}


float2 rotate(float2 pt, float2 n)
{
        float2 ptTransformed;
        ptTransformed.x = n.r * pt.x - n.g * pt.y;
        ptTransformed.y = n.g * pt.x + n.r * pt.y;

        return ptTransformed;
}


/** The ssao shader returning the an intensity value between 0 and 1
*/
float ssao(fragment IN,
                   uniform sampler2D positions,
                   uniform sampler2D noiseTexture,
                   uniform float2 samples[NUM_SAMPLES],
                   uniform float3 currentNormal,
                   uniform float3 currentViewDir,
                   uniform float noiseMultiplier,
                   uniform float4 centerPosition
                   )
{
        // the w coordinate from the persp. projection
        float w = centerPosition.w;

        // Check in a circular area around the current position.
        // Shoot vectors to the positions there, and check the angle to these positions.
        // Summing up these angles gives an estimation of the occlusion at the current position.

        float total_ao = 0.0;

        const float areaSize = 5e-1f;

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

                //sample noisetex; r stores costheta, g stores sintheta
                //float2 mynoise = tex2D(noiseTexture, IN.texCoord.xy * noiseMultiplier).xy * 2.0f - 1.0f;
                float2 mynoise = tex2D(noiseTexture, IN.texCoord.xy * noiseMultiplier).xy;

                // rotation
                //float2 offsetTransformed = offset;
                //float2 offsetTransformed = rotate(offset, mynoise);
                float2 offsetTransformed = reflect(offset, mynoise);

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

                // sample downsampled texture in order to speed up texture accesses
                float3 sample_position = tex2Dlod(positions, float4(texcoord, 0, 1)).xyz;
                //float3 sample_position = tex2D(positions, texcoord).xyz;

                float3 vector_to_sample = sample_position - centerPosition.xyz;
                float length_to_sample = length(vector_to_sample);
                float3 direction_to_sample = vector_to_sample / length_to_sample;

                // Angle between current normal and direction to sample controls AO intensity.
                float cos_angle = dot(direction_to_sample, currentNormal);
                cos_angle = max(cos_angle, 0.0f);

                // distance between current position and sample position controls AO intensity.
                float distance_intensity = 
                        (SAMPLE_INTENSITY * DISTANCE_SCALE) / (DISTANCE_SCALE + length_to_sample * length_to_sample);

                // if surface normal perpenticular to view dir, some samples probably count less 
                // => compensate for this
                float view_correction = 1.0f + VIEW_CORRECTION_SCALE * (1.0f - dot(currentViewDir, currentNormal));

                total_ao += cos_angle * distance_intensity * view_correction;
        }

        return (1.0f - total_ao);
        //return dot(currentViewDir, currentNormal);
}


/** Computes ambient occlusion + diffuse reflections
*/
float4 globIllum(fragment IN,
                                 uniform sampler2D colors,
                                 uniform sampler2D positions,
                                 uniform sampler2D noiseTexture,
                                 uniform float2 samples[NUM_SAMPLES],
                                 uniform float3 currentNormal,
                                 uniform float3 currentViewDir,
                                 uniform float noiseMultiplier,
                                 uniform float4 centerPosition
                                 )
{
        // the w coordinate from the persp. projection
        float w = centerPosition.w;

        // Check in a circular area around the current position.
        // Shoot vectors to the positions there, and check the angle to these positions.
        // Summing up these angles gives an estimation of the occlusion at the current position.

        float total_ao = 0.0;
        float3 total_color = float3(0.0f);

        const float areaSize = 5e-1f;

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

                //sample noisetex; r stores costheta, g stores sintheta
                float2 mynoise = tex2D(noiseTexture, IN.texCoord.xy * noiseMultiplier).xy * 2.0f - 1.0f;

                // rotation
                float2 offsetTransformed = rotate(offset, mynoise);

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

                float3 sample_position = tex2D(positions, texcoord).xyz;
                float3 sample_color = tex2D(colors, texcoord).xyz;

                float3 vector_to_sample = sample_position - centerPosition.xyz;
                float length_to_sample = length(vector_to_sample);
                float3 direction_to_sample = vector_to_sample / length_to_sample;

                // Angle between current normal and direction to sample controls AO intensity.
                float cos_angle = dot(direction_to_sample, currentNormal);
                cos_angle = max(cos_angle, 0.0f);

                // distance between current position and sample position controls AO intensity.
                float distance_intensity = 
                        (SAMPLE_INTENSITY * DISTANCE_SCALE) / (DISTANCE_SCALE + length_to_sample * length_to_sample);

                // if normal perpenticular to view dir, only half of the samples count
                float view_correction = 1.0f + VIEW_CORRECTION_SCALE * (1.0f - dot(currentViewDir, currentNormal));

                total_ao += cos_angle * distance_intensity * view_correction;
                total_color += cos_angle * distance_intensity * view_correction * sample_color * 0.3f;
        }

        return float4(total_color, 1.0f - total_ao);
}


/** The mrt shader for screen space ambient occlusion
*/
pixel main(fragment IN, 
                   uniform sampler2D colors,
                   uniform sampler2D positions,
                   uniform sampler2D normals,
                   uniform sampler2D noiseTexture,
                   uniform float2 samples[NUM_SAMPLES],
                   uniform float noiseMultiplier,
                   uniform sampler2D oldTex,
                   const uniform float4x4 oldModelViewProj,
                   uniform float maxDepth,
                   uniform float expFactor
                   )
{
        pixel OUT;

        float4 normal = tex2D(normals, IN.texCoord.xy);
        
        // the ambient term
        float amb = normal.w;

        // expand normal
        normal = normalize(normal);// * 2.0f - 1.0f);
        /// the current view direction
        float3 viewDir = normalize(IN.view * 2.0f - float3(1.0f));

        // the current world position
        float4 centerPosition = tex2D(positions, IN.texCoord.xy);
        
        float4 col = tex2D(colors, IN.texCoord.xy);
        float currentDepth = col.w;

        float ao = ssao(IN, positions, noiseTexture, samples, normal.xyz, viewDir, noiseMultiplier, centerPosition);
        float4 attenuated_color = ao * col;
        //float4 attenuated_color = ao;

        //float4 new_col = globIllum(IN, colors, positions, noiseTexture, samples, normal.xyz, viewDir, noiseMultiplier, centerPosition); 
        //float4 attenuated_color = ao * col + new_col;
        
        const float x = expFactor;

        float4 dummy = centerPosition * maxDepth;
        dummy.w = 1.0f;

        float4 oldPos = mul(oldModelViewProj, dummy);

        float newDepth = oldPos.z / oldPos.w;
 
        float2 tex = (oldPos.xy / oldPos.w) * 0.5f + 0.5f;
        float4 col1 = tex2D(oldTex, tex);

        float oldDepth = col1.w;
        float depthDif = 1.0f - newDepth / oldDepth;

        if ((tex.x >= 0.0f) && (tex.x < 1.0f) && 
                (tex.y >= 0.0f) && (tex.y < 1.0f) && 
                (abs(depthDif)  < 1e-4f))
        {
                OUT.color = attenuated_color * expFactor + col1 * float4(1.0f - expFactor);
        }
        else
        {
                OUT.color = attenuated_color;
        }

        //OUT.color.xyz = viewDir;
        //OUT.color = attenuated_color;
        
        OUT.color.w = currentDepth;

        return OUT;
}