View Full Version : Emulating Blinn shading in OpenGL
09-28-2009, 07:58 AM
We posted this in the Maya forum but got no replies, maybe we have more luck here.
We want to emulate the Maya blinn shading in OpenGL. For phong shading we know the specular light intensity is given by: (R dot V)^alpha
Where alpha equals cosine power in Maya.
Maya uses eccentricity and specular roll off parameters in the Blinn formula.
How is the specular light intensity formula for Blinn shading using these parameters?
Boyo and Tom
09-28-2009, 10:13 PM
This guy (http://area.autodesk.com/forum/autodesk-maya/lighting---rendering/writing-my-own-blinn-shader/)at the AREA forums seems to be in the same boat as you and had this to say:
I’m assuming maya uses the Trowbridge and Reitz proposed distribution function in that there appears an eccentricity just the like one in Maya’s Blinn attributes.
If this is the distribution used, what does specular roll off represent in the equation, and does it take the fresnel reflection into account to - if so, what is the assumed refraction index.
And then ...
Now that I look at the equation again, I’m thinking specular roll off must be the n in the Fresnel reflection function....
But that's only on page one of a google search. (http://www.google.com/search?q=openGL+blinn+shader+specular+rolloff+eccentricity&ie=utf-8&oe=utf-8&aq=t&rls=org.mozilla:en-US:official&client=firefox-a) Good luck with this - it sounds great. Too bad the other guy didn't post his :(
09-29-2009, 10:01 AM
Attention: The Maya Blinn is actually no classic Blinn illum model but rather a Torrance-Sparrow model:
http://www.creativecrash.com/forums/api/topics/maya-blinn. this also was confirmed in the Maya Knowledge-Base, but I unfortunately don't have access to this at the moment.
Edit: Huh - it's even mentioned in the maya docs: http://download.autodesk.com/us/maya/2010help/Nodes/blinn.html
09-29-2009, 10:02 AM
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