Horizon Split Ambient Occlusion

February 27, 2008 at 3:55 am (Game techniques, Presentations)

I have so much I want to write about what I saw at I3D and GDC that sitting down and doing it seems daunting. I will try and post my thoughts over the next few days.

One interesting poster at I3D (and also a short talk at GDC) was an extension to SSAO. The idea was to calculate a piece-wise linear approximation of the horizon ala horizon mapping. This is achieved by sampling the depth values along m steps ( they used 8 ) in n equally spaced directions (8 again) in the tangent frame. At each depth sample, you update the horizon value if the current depth sample is higher than the current estimation of the horizon in that direction. Sampling in this fashion reduces over-occlusion. This is actually very similar to the approximation to AO that Dachsbacher and Tatarchuk described in their poster at I3D last year, “Prism Parallax Occlusion Mapping with Accurate Silhouette Generation“. All of the authors from the poster are NVIDIA guys and they announced that they will release a whitepaper describing their method.


  1. repi said,

    Sounds interesting, looking forward to the paper to be released

  2. Stephen Hill said,

    The slides are available in the meantime:

  3. gjoel said,

    The whole prism-thing in turn looks very much inspired by the Generalized Displacement Mapping (and the prior View-dependent Displacement Mapping)

    Click to access esr_wx.pdf


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