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Third of the lighting models

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jollyjeffers

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First off a brief service announcement: >10000 hits on my journal. Yay! Many thanks to all of you who deemed my ramblings worth reading..

Oren-Nayar

Another lighting model similar to Cook-Torrance in that it attempts to modify the lambertian model to compensate for a rough surface. The key difference to Cook-Torrance is that Oren-Nayar's doesn't include a specular component. Most implementations attach a standard Blinn-Phong specular term if it's needed.

So, the equation I'm using (which has been the hardest to comprehend so far [headshake]) is as follows:



Inputs:
  • Diffuse Texture
  • Roughness Texture
  • Normal Map Texture
  • Sin()Tan() Lookup Texture

  • Ambient Constant
  • Light Position
  • Light Range
  • Light Falloff

  • World Matrix
  • World * View * Proj Matrix

    Vertex Data:
  • Position
  • Normal
  • Tangent
  • TexCoord

    With regards to the generic base that I'm trying to derive, the following is noteworthy:
  • No specular texture. Implementation might add this via a Blinn-Phong component though.
  • Sin()Tan() lookup texture needs to be generated and provided
  • Uses a roughness texture, same as Cook-Torrance
  • No equation-specific constants

    And, as you should be expecting, a visio diagram to encapsulate the above steps:
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    The 10000th read was me :)

    I know because the counter was at 9999 when i clicked on your journal. I wanted to leave a comment stating "victory", but a collegue distracted me with a question, and when i was back 10 minutes later, i forgot to do it :)

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    Hi, I like your posts about the lighting models and hope you make more of them (anisotropic stuff!), oh and some pretty pictures showing off each one :)

    I'm ending up with a different formula for Alpha/Beta though. You had
    Quote:
    Original post by jollyjeffers
    alpha = min( dot(Normal, Light), dot(Normal, View) )
    beta = max( dot(Normal, Light), dot(Normal, View) )

    and I'v got (I hope, in accordance with the original paper (p.22))

    theta_r = acos( dot(Normal, Light) )
    theta_i = acos( dot(Normal, View) ) )
    alpha = max( theta_r, theta_i )
    beta = min( theta_r, theta_i )

    So the difference is that you are using the cosine of the angles instead of the angles when you feed them into Sin/Tan. I guess you could probably skip the acos if your Sin/Tan are tweaked lookup tables though.

    Sorry about posting so far down you journal, hope you notice it :)

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