Shading Technique - FXAA

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These code snippets demonstrate how to set up an anti-aliasing filter that smoothes the image displayed on the screen. There are many ressources available for the exact math (e.g. Nvidia) behind FXAA and new variants are developed regularly.

It has been created by worstplayer.


The Shader

[[FX]]

// Samplers
sampler2D buf0 = sampler_state {
        Address = Clamp;
        Filter = None;
};

context FXAA {
        VertexShader = compile GLSL VS_FSQUAD;
        PixelShader = compile GLSL FS_FXAA;
}



[[VS_FSQUAD]]

uniform mat4 projMat;
attribute vec3 vertPos;
varying vec2 texCoords;
                                
void main(void) {
        texCoords = vertPos.xy; 
        gl_Position = projMat * vec4( vertPos, 1 );
}


[[FS_FXAA]]

uniform sampler2D buf0;
uniform vec2 frameBufSize;
varying vec2 texCoords;

void main( void ) {
        //gl_FragColor.xyz = texture2D(buf0,texCoords).xyz;
        //return;

        float FXAA_SPAN_MAX = 8.0;
        float FXAA_REDUCE_MUL = 1.0/8.0;
        float FXAA_REDUCE_MIN = 1.0/128.0;

        vec3 rgbNW=texture2D(buf0,texCoords+(vec2(-1.0,-1.0)/frameBufSize)).xyz;
        vec3 rgbNE=texture2D(buf0,texCoords+(vec2(1.0,-1.0)/frameBufSize)).xyz;
        vec3 rgbSW=texture2D(buf0,texCoords+(vec2(-1.0,1.0)/frameBufSize)).xyz;
        vec3 rgbSE=texture2D(buf0,texCoords+(vec2(1.0,1.0)/frameBufSize)).xyz;
        vec3 rgbM=texture2D(buf0,texCoords).xyz;
        
        vec3 luma=vec3(0.299, 0.587, 0.114);
        float lumaNW = dot(rgbNW, luma);
        float lumaNE = dot(rgbNE, luma);
        float lumaSW = dot(rgbSW, luma);
        float lumaSE = dot(rgbSE, luma);
        float lumaM  = dot(rgbM,  luma);
        
        float lumaMin = min(lumaM, min(min(lumaNW, lumaNE), min(lumaSW, lumaSE)));
        float lumaMax = max(lumaM, max(max(lumaNW, lumaNE), max(lumaSW, lumaSE)));
        
        vec2 dir;
        dir.x = -((lumaNW + lumaNE) - (lumaSW + lumaSE));
        dir.y =  ((lumaNW + lumaSW) - (lumaNE + lumaSE));
        
        float dirReduce = max(
                (lumaNW + lumaNE + lumaSW + lumaSE) * (0.25 * FXAA_REDUCE_MUL),
                FXAA_REDUCE_MIN);
          
        float rcpDirMin = 1.0/(min(abs(dir.x), abs(dir.y)) + dirReduce);
        
        dir = min(vec2( FXAA_SPAN_MAX,  FXAA_SPAN_MAX),
                  max(vec2(-FXAA_SPAN_MAX, -FXAA_SPAN_MAX),
                  dir * rcpDirMin)) / frameBufSize;
                
        vec3 rgbA = (1.0/2.0) * (
                texture2D(buf0, texCoords.xy + dir * (1.0/3.0 - 0.5)).xyz +
                texture2D(buf0, texCoords.xy + dir * (2.0/3.0 - 0.5)).xyz);
        vec3 rgbB = rgbA * (1.0/2.0) + (1.0/4.0) * (
                texture2D(buf0, texCoords.xy + dir * (0.0/3.0 - 0.5)).xyz +
                texture2D(buf0, texCoords.xy + dir * (3.0/3.0 - 0.5)).xyz);
        float lumaB = dot(rgbB, luma);

        if((lumaB < lumaMin) || (lumaB > lumaMax)){
                gl_FragColor.xyz=rgbA;
        }else{
                gl_FragColor.xyz=rgbB;
        }
}



The Material

<Material>
        <Shader source="fxaa.shader"/>
</Material>


The pipeline

Basically, the normal geometry is rendered to a new buffer instead of straight to the screen. Afterwards, the new FXAA shader works over this buffer and renders to screen.

<Pipeline>
        <Setup>
                <RenderTarget id="FINALIMAGE" depthBuf="true" numColBufs="1" format="RGBA16F" scale="1.0" maxSamples="0" />
        </Setup>
    
        <CommandQueue>
                <Stage id="Ambient">
            <SwitchTarget target="FINALIMAGE" />
                        <ClearTarget depthBuf="true" colBuf0="true" />
                        
                        <DrawGeometry context="AMBIENT" class="~Translucent" />
        </Stage>
                
                <Stage id="Lighting">
                        <DoForwardLightLoop class="~Translucent" />
                </Stage>
                
                <Stage id="Translucent">
                        <DrawGeometry context="TRANSLUCENT" class="Translucent" />
                </Stage>
                
        <!-- -->
        <Stage id="FXAA">
            <SwitchTarget target="" />
                        <BindBuffer sampler="buf0" sourceRT="FINALIMAGE" bufIndex="0" />
            <DrawQuad material="fxaa.material.xml" context="FXAA" />
            <UnbindBuffers />
                </Stage>
        <!-- -->
        
        
                <Stage id="Overlays">
                        <DrawOverlays context="OVERLAY" />
                </Stage>
        </CommandQueue>
</Pipeline>
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