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Re: OpengGL color / material properties
September 06, 2013 05:04PM
Hi Travis,

I agree, re: the scoping rules. For the actual file, I think we might want to have meta-tokens (e.g. like "rubber" and "chrome") and let the visualization app implement a series of known effects, rather than having a specific image technology.

- The number of "bumpy textures" in our brickset is, at least I think, relatively small.
- The rendering technology to be implemented might be rather variable.

For example, a fixed-function renderer could intentionally hack the specularity params to do gritty reflections and at least the overall specularity would be correct. But if provided with an actual bump map, if the renderer can't use it directly, it has no way to know what was intended. I think providing actual bump map images externally is most useful when

(1) the bump map must match the location of a texture map exactly (e.g. this is the extrusion of the painted thing you see) and/or
(2) when the bump map's UV-coordinate application is custom to the model, rather than just a repeating pattern.

The actual bump maps are typically 8-bits per channel; in X-Plane we hit the case where some very smooth, very shallow bump maps showed banding of specular hilites due to the precision limit. We solved this by in some cases adding a scaler factor so that the 8-bits of precision could be used for the full range of bump-perturbations or for high precision very subtle effects. While a number of normal mapping schemes are possible, tangent space bump mapping is often popular because the normal map can be used just like the texture it matches.

Some apps stash the original height map from which the normal map was derived into another texture channel; this lets the app extrude geometry or apply parallax effects to the normal map. (http://en.wikipedia.org/wiki/Parallax_mapping)

Cheers
Ben
SubjectAuthorViewsPosted
OpengGL color / material properties Roland Melkert420August 25, 2013 12:45PM
Re: OpengGL color / material properties Ben Supnik192August 25, 2013 03:33PM
Re: OpengGL color / material properties Roland Melkert172August 25, 2013 04:27PM
Re: OpengGL color / material properties Travis Cobbs191August 26, 2013 01:12PM
Re: OpengGL color / material properties Roland Melkert230August 26, 2013 03:59PM
Re: OpengGL color / material properties Roland Melkert197September 03, 2013 09:47AM
Re: OpengGL color / material properties Travis Cobbs196September 03, 2013 12:26PM
Re: OpengGL color / material properties Roland Melkert193September 04, 2013 11:45AM
Re: OpengGL color / material properties Ben Supnik212September 03, 2013 01:07PM
Re: OpengGL color / material properties Roland Melkert194September 04, 2013 11:49AM
Re: OpengGL color / material properties Ben Supnik209September 04, 2013 07:02PM
Re: OpengGL color / material properties Roland Melkert177September 05, 2013 09:32AM
Re: OpengGL color / material properties Steffen197September 05, 2013 02:08PM
Re: OpengGL color / material properties Ben Supnik156September 05, 2013 07:33PM
Re: OpengGL color / material properties Travis Cobbs139September 06, 2013 09:52AM
Re: OpengGL color / material properties Steffen159September 06, 2013 12:26PM
Re: OpengGL color / material properties Steffen146September 06, 2013 12:27PM
Re: OpengGL color / material properties Travis Cobbs178September 06, 2013 01:07PM
Re: OpengGL color / material properties Ben Supnik181September 06, 2013 02:14PM
Re: OpengGL color / material properties Travis Cobbs230September 06, 2013 02:46PM
Re: OpengGL color / material properties Ben Supnik226September 06, 2013 05:04PM
Re: OpengGL color / material properties Travis Cobbs209September 06, 2013 07:30PM
Re: OpengGL color / material properties Ben Supnik266September 07, 2013 05:16PM
Re: OpengGL color / material properties Allen Smith194September 05, 2013 10:03AM



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