[opensource-dev] Review Request: STORM-1823 - Replace current specular model with Normalized Blinn-Phong specularity

[Geenz Spad]

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This is an automatically generated e-mail. To reply, visit:
http://codereview.secondlife.com/r/565/
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(Updated March 25, 2012, 2:07 p.m.)


Review request for Viewer and David Parks.


Changes
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Added more information as to why we multiply in our shaders, and why we're scaling our results by (1.f / 6) in our LUT creation.
Also renamed handleReleaseLUTBufferChanged to handleLUTBufferChanged, per Tofu's request.


Description
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For a while now, Second Life's deferred renderer has had a somewhat "toonish" looking specular model, as opposed to other platforms which try to go for more physically accurate looking models, such as blinn-phong and similar.

This feature changes the specular model to a technique called normalized blinn-phong. The specular model applies the usual blinn-phong term (assume NdotV to the power of n), multiplied by a normalization function of:
((n + 2) * (n + 4)) / (8 * PI * (powf(2, -n/2) + n))
Where n is the specular exponent.

Gamma correction is also applied to the result to bring the visual results more in line with what you see in high end game engines such as Unreal Engine 3 and Frostbite 2, and stored in a lookup texture.

Test plan can be found in the JIRA.
Repository can be found here: https://bitbucket.org/Geenz/viewer-nbp


This addresses bug STORM-1823.
    http://jira.secondlife.com/browse/STORM-1823


Diffs (updated)
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  indra/newview/app_settings/shaders/class1/deferred/softenLightF.glsl b32595c5170f92ac2dbab635955b1b86634f1475 
  indra/newview/app_settings/shaders/class1/deferred/pointLightF.glsl b32595c5170f92ac2dbab635955b1b86634f1475 
  indra/newview/app_settings/shaders/class1/deferred/multiPointLightF.glsl b32595c5170f92ac2dbab635955b1b86634f1475 
  indra/newview/app_settings/shaders/class2/deferred/softenLightF.glsl b32595c5170f92ac2dbab635955b1b86634f1475 
  indra/newview/llviewercontrol.cpp b32595c5170f92ac2dbab635955b1b86634f1475 
  indra/newview/pipeline.cpp b32595c5170f92ac2dbab635955b1b86634f1475 

Diff: http://codereview.secondlife.com/r/565/diff/diff


Testing
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* Tested performance characteristics - both Normalized Blinn-Phong and the previous model seem to have the same performance
* Checked the perceived "brightness" of the new highlights vs. the old ones - new ones seem much brighter at higher shiny values than the old ones, and seem much less "cartoonish" as such
* Checked the impact on different bumpiness values at the test rig at Hippo Hollow - noticeable visual improvement across all objects (though low shiny seems to have a much more subtle light reflectance term - this is expected for normalized blinn-phong)
* Tested different LUT resolutions - best looking seems to be 512x128 with seemingly no measurable decrease in performance

You can find the latest build here: http://automated-builds-secondlife-com.s3.amazonaws.com/hg/repo/oz_project-8/rev/251711/index.html


Thanks,

Geenz Spad

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