In the documentation, it writes that the raytracing must keep the whole scene in memory, so I am wondering if it is better to switch to the raytrace hider when I need raytracing shadows or any raytracing type. Because the renderer will have to keep the whole scene when it meet a function raytracing, although I set the renderer into stochastic hider.
Moreover, in stochastic, I never get some good results with raytracing, like aliased shadows, and even if I low the shading rate, the renderer begins run so slow.
The stochastic shader in general produce faster results. In general, the only reason you would want to use the raytrace hider is if you have a very expensive shader that you only want to execute on visible points. Even though stochastic hider has occlusion culling, it will still shade some points that are invisible.
If you see any problems with the stochastic hider, please send us a RIB+shaders so we can figure out what the problem is.
I have do some tests back for showing some raytracing issues:
In the image http://daohungh.free.fr/Renderman/renderman1%5bCamera%5d.rgb.0001.PNG,
it is a normal render, the shading and trace bias values are not changed, the render time is 30s. We can see the shadow artifacts on the skin.
So I try to set the trace bias in order to prevent this problem. Here another render http://daohungh.free.fr/Renderman/renderman2%5bCamera%5d.rgb.0001.PNG.
The render time is 50s. The image is better, but I can still see some shadow aliasing.
So I must play with the shading rate, I set at 0.4, finally the result is good enough http://daohungh.free.fr/Renderman/renderman3%5bCamera%5d.rgb.0001.PNG , but now the render time is 126s.
Though we can notice there are some odd noise shading on all the images, I have not found the cause.
till now, the renders were made with the stochastic hider. So I decided to try with the raytrace hider, the shading rate is set back to default. Here the render http://daohungh.free.fr/Renderman/renderman4%5bCamera%5d.rgb.0001.PNG
The result seems like the same as the third render, but the render time is better, about 88s.
I have uploaded the rib/shaders there
there the files are.
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