source: GTP/trunk/App/Demos/Vis/FriendlyCulling/src/shaders/ambient_occlusion.fx @ 2810

//=======================================================================================
string description = "Screenspace Ambient Occlusion";
//=======================================================================================


//=======================================================================================


#define SAMPLES                         24

static const float2 samples[SAMPLES] =
        {
                {-0.326212f, -0.405805f},
                {-0.840144f, -0.07358f},
                {-0.695914f, 0.457137f},
                {-0.203345f, 0.620716},
                {0.96234f, -0.194983f},
                {0.473434f, -0.480026f},
                {0.519456, 0.767022f},
                {0.185461f, -0.893124f},
                {0.507431f, 0.064425f},
                {0.89642f, 0.412458f},
                {-0.32194f, -0.932615f},
                {-0.791559f, -0.597705f},
                {0.326212f, 0.405805f},
                {0.840144f, 0.07358f},
                {0.695914f, -0.457137f},
                {0.203345f, -0.620716},
                {-0.96234f, 0.194983f},
                {-0.473434f, 0.480026f},
                {-0.519456, -0.767022f},
                {-0.185461f, 0.893124f},
                {-0.507431f, -0.064425f},
                {-0.89642f, -0.412458f},
                {0.32194f, 0.932615f},
                {0.791559f, 0.597705f}
        };
        
        
//=======================================================================================


float4x4 WorldViewProj                  : WorldViewProjection;
float4x4 WorldView                              : WorldView;

float4x4 CameraViewProjection;

shared float3 WorldCenterPosition;              // Center positions around this point (usually eye point).
shared float WorldScale;                                // Scale positions to maintain precision.

float AreaSize = 1.0;
float SampleIntensity = 0.1;


//=======================================================================================


shared texture positions;
shared texture diffuse;
shared texture normals;

sampler PositionsSampler = sampler_state 
{
    texture = <positions>;
    AddressU  = CLAMP;        
    AddressV  = CLAMP;
    AddressW  = CLAMP;
    MINFILTER = POINT;
    MAGFILTER = POINT;
    MIPFILTER = NONE;
};

sampler DiffuseSampler = sampler_state 
{
    texture = <diffuse>;
    AddressU  = CLAMP;        
    AddressV  = CLAMP;
    AddressW  = CLAMP;
    MINFILTER = POINT;
    MAGFILTER = POINT;
    MIPFILTER = NONE;
};

sampler NormalsSampler = sampler_state 
{
    texture = <normals>;
    AddressU  = CLAMP;        
    AddressV  = CLAMP;
    AddressW  = CLAMP;
    MINFILTER = POINT;
    MAGFILTER = POINT;
    MIPFILTER = NONE;
};


//=======================================================================================


struct VertexInput {
        float4 position                 : POSITION;
        float2 texcoord                 : TEXCOORD0;
};

struct VertexOutput {
        float4 position                 : POSITION;
        float2 texcoord                 : TEXCOORD0;
};

struct PixelOutput {
        float4 color                    : COLOR0;
};


//=======================================================================================


VertexOutput vs_render(VertexInput IN)
{
        VertexOutput OUT;

        OUT.position = float4(IN.position.xyz, 1.0);
        OUT.texcoord = IN.texcoord;
        
        return OUT;
}


//=======================================================================================


PixelOutput ps_render(VertexOutput IN)
{
        PixelOutput OUT;

        float4 positions = tex2D(PositionsSampler, IN.texcoord);
        float4 normals = tex2D(NormalsSampler, IN.texcoord);
        
        float3 current_position = positions.xyz;
        float3 current_normal = normals.xyz * 2.0 - 1.0;
        
        // Get postprojection Z value to adjust AO area size.
        float3 worldposition = (positions.xyz / WorldScale) + WorldCenterPosition;
        float4 projected_position = mul(float4(worldposition.xyz, 1.0), CameraViewProjection);
        projected_position.xyz /= projected_position.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;

        for (float sample = 0.0; sample < SAMPLES; sample++)
        {
                float2 offset = samples[sample];
                float2 texcoord = IN.texcoord + offset * AreaSize * (1.0 - projected_position.z);
                
                float3 sample_position = tex2D(PositionsSampler, texcoord).xyz;
                
                float3 vector_to_sample = sample_position - current_position;
                float length_to_sample = length(vector_to_sample);
                float3 direction_to_sample = vector_to_sample / length_to_sample;
                length_to_sample /= WorldScale;
                
                // Angle between current normal and direction to sample controls AO intensity.
                float angle = dot(direction_to_sample, current_normal);
                angle = max(angle, 0.0);
                
                // Distance between current position and sample position controls AO intensity.
                float distance_intensity = 1.0 - length_to_sample * 2.0;
                distance_intensity = max(distance_intensity, 0.0);
                
                total_ao += angle * SampleIntensity * distance_intensity;
        }
        
        
        OUT.color = float4(0.0, 0.0, 0.0, total_ao);
        
        return OUT;
}


//=======================================================================================


technique render
{
        pass p0
        {
                VertexShader = compile vs_3_0 vs_render();
                PixelShader = compile ps_3_0 ps_render();       
        }
}