Jpatch and Aqsis help

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Jpatch and Aqsis help

Postby animohn » Tue Aug 30, 2005 4:26 pm

I’ve been trying to learn how to use aqsis with jpatch animator and after 2 days of reading whatever I could find about using renderman I just can’t seem to get shadows to appear. I believe I understand what I’m suppose to be doing with shadow light shaders and all but no luck. :oops:
Does anyone have (or could possibly make) a simple jpatch file that creates a shadow using aqsis so I can finally figure this thing out. Many thanks in advance.
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Postby sascha » Tue Aug 30, 2005 4:55 pm

The two most commonly used algorithms to compute shadows in a photorealistic renderer are raytracing and shadow maps.

If you use a raytracer like POV-Ray (or a hybrid renderer such as PrMan or 3Delight) you can turn on raytraced shadows and get them for free.
A pure REYES renderer (such as Aqsis) can only use shadow maps - and they have to be generated before they can be used.

Right now JPatch does not automate this process. You'd have to manually tewak the RIB files JPatch generates. I have little expirence with RenderMan, but I will dig into it, and once I figured out how, JPatch will automatically generate the shadow maps.

A related topic is reflections. Again, they come for free in a raytracer, but pure REYES renderers need environment maps.

PS: I plan to render my next animation for the IRTC with Aqsis. It's likely that some features (e.g to create shadowmaps automatically) drop off as a by-product
If someone has more expirence with REYES renderers, perhaps they could help out with some tips on shadow/environment map generation.

For the time being it might be easier to use a RIB renderer that can do raytracing (like Pixie, BMRT, 3Delight, PrMan) and write shaders that utilize it. AFAIK Aqsis will get a raytracer in a future version.

Better RIB support is on my todo list, it just isn't "on top" right now, and I have to learn more about RenderMan first.

PS: I plan to render my next IRTC animation with Aqsis - it's quite likely that some tools (e.g. automatic shadowmap generation) drop off as a by-product ;-)
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Postby Torf » Tue Aug 30, 2005 7:12 pm

sascha wrote:PS: I plan to render my next IRTC animation with Aqsis

This has nothing to do with the topic, but I'd like to know why you plan to use Aqsis. I just checked out its website and the gallery, and the images did not really impress me (didn't check them all, though). So do you have any specific reasons for using Aqsis?
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Postby sascha » Tue Aug 30, 2005 10:28 pm

I'm really a POV-Ray fan, but I also know that it has several limitations that make rendering a high-quality animation almost impossible:

* No support for Catmull Clark subdivision surfaces (these are standard now and have replaced NURBS for most applications, but well, POV didn't even support NURBS).
* No/poor support for motion blur.
* Slow (because accurate) focal blur.
* No shader antialiasing (e.g. the "checkered floor" aliases badly in animations once the squares are smaller than a pixel).
* No displacement mapping (unless you'd like to use Isosurfaces for character animation ;-)
* Limited procedural textures.
* No support for reference geometry (3D textures won't "stick" on an animated model).
* No support for curve primitives (hair, grass, fur,...)
* Limited lighting system

(of course POV-Ray has other strenghts and some nice unique features!)

There have been several endless discussions on the POV-Ray newsgroups about Ray-Tracing vs. scanline rendering. Fact is that Pixar has designed REYES (years ago) to address all of those problems mentioned above - and almost any CGI shot you'll see in cinema (no matter if photorealistic or toon-style) has been rendered with a RenderMan renderer.
Modern RenderMan renderers use a hybrid approach (REYES + raytracing when needed), but their raytracers are much more powerful than POV-Ray, at least in those areas I've mentioned above.

RenderMan is very flexible - you can write your own shaders (including surface, displacement, volume and light-shaders), and REYES is very fast and produces very high quality images. But it's much more difficult to learn and use than e.g. POV-Ray, I guess that's the reason why you won't find many stunning pictures on the Aqsis homepage. (Aqsis's quite new though).

Long story short, I'd like to improve JPatch's RIB export and I'd like to learn RenderMan. I'd like to give Aqsis a try because it's open source - if for any reasons it doesn't work I can fallback to another RenderMan renderer (e.g. 3Delight, it's commercial but free for non-commercial use).

Some film frames rendered with 3Delight are here:
http://www.3delight.com/renderman_gallery.htm
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Postby Torf » Wed Aug 31, 2005 7:47 am

sascha wrote:Catmull Clark subdivision surfaces (these are standard now and have replaced NURBS for most applications, but well, POV didn't even support NURBS).

Heh, just found out that the paper describing subdivision surfaces dates back to 1978. Boy, some guys are really ahead of their time!

I've notived some of POV's problem you mention, too (as does everybody who uses POV-Ray for a while). What I'm missing most are shaders and some more animation tools (IK, bones). But until today (and for some more time, I guess), POV has more features than I got time to learn them, so no need for a change here. I can understand your motivation, though :D
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Postby sascha » Wed Aug 31, 2005 8:54 am

The "problem" is that most people don't see POV-Ray as a renderer, but as a modeling and animation tool as well. While some features are certainly nice to have, they don't - in my opinion - belong into a renderer (e.g. mech- or cloth simulation) . All modeling and animation issues belong into a tool with a graphical user-interface - it's just cumbersome to change some lines in POV-code, wait 10 hours until the test-animation finished rendering, change another line, wait another 10 hours... GUIs give you instant feedback.
IMHO the POV team should focus on the rendering features, as POV-Ray lacks behind there.
The second problem is that most people use POV-Ray to create stills - thus many shortcomings don't weight heavy. You don't really need reference geometry, motion blur or good antialiasing in stills. Many things can be worked around (they take longer to render but produce better results - e.g. a higher level of supersampling to compensate for the missing shader antialiasing). This is all ok for stills - after all, when rendering in the night, who cares if the image takes 2 or 10 hours to complete. With animations, it does make a difference if the animation takes one night or one week to render.

But don't worry. JPatch will always support POV-Ray! But RenderMan is sort of an "industry standard" and its quite interesting, so I hope I can better support RenderMan renderers in future versions of JPatch.
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