Santiago Pacheco's Portfolio: Shaders - Fast Aproximate Screen Space Reflections

Shaders - Fast Aproximate Screen Space Reflections

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A while back, when working on my first engine, Atom Engine (DirectX 9), I played a bit with shaders for reflections. A fast but extremely hacky method to get them is to grab the pixel coordinates (in screen space), and negate them in the y or x axis. Then just add them up with the color.

In practice, it works quite good.
You can extend it by adding a lot of blur, and also by using the surface normal to select the axist to negate. For example, negating both the x and y axis and using the reflection vector to mix both.

Below there are a couple screens, that just negate the y axis, and add ~~too little~~ some blur.

Works best for planar surfaces

The black regions are caused by the addressing mode. Should be set to wrap

Shader Snippet (HLSL) for the simple case

    // sspixel = coordinates in screen space (normalized 0 to 1)
    float2 newPixel = sspixel;
    newPixel.y = 1 - newPixel.y;
    
    // DX 9 Style
    float3 reflection = tex2D(texSampler,newPixel);
    // DX >10 Style
    //float3 reflection = colTexture.SampleLevel(texSampler,newPixel,0);

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