[Sidefx-houdini-list] random fur scale
ivan at martian-labs.com
Mon Feb 11 19:24:28 EST 2008
actually, VEX usually executes faster than c++ code, unless you spend as much
time optimizing your code as SESI did optimizing VEX. The SIMD architecture
lines the data up niceley for the CPU, but it's a friggin nightmare to think it
through as a human being.
the volumetric system in Houdini is actually wicked fast- I've written my own in
VEX before and in c++. Both were a LOT slower. There's definiteley a ton of
optimization going on in there, probably in the c++ code and how it uses the
VEX you write...
Quoting Pablo Giménez <pablogipi at gmail.com>:
> 2008/2/12, Fred Valleur <fred.valleur at gmail.com>:
> > Hi,
> > a CVex shader is called from a compiled C++ dso (or dll on windows). It
> > is
> > written in VEX and let you modify data used by the compiled plugin. It
> > offers great flexibility as you don't have to "hard-code" everything in
> > C++.
> > The fur SOP/Geometry shader is a good example to look at. The hair
> > generation and memory allocation is handled by the C++ plugin, but it
> > calls
> > two CVex Shaders that can modify hair/points attribute to change the look
> > of
> > the fur.
> I am guessing here but ... maybe this can be used to speedup volumetrics, do
> all the raymarching hard stuff in C++, more times faster than VEX, and use
> VEX only to modify every step sample.
> The raymarching loop and some fancy adaptative step formula can be done in
> c++, only guessing.
> This way, you can write your own kink/frizz funtions in VEX and let the C++
> > code handle the "low level" hair generation.
> > Hope this makes it a bit clearer,
> > Cheers,
> > Fred.
> > --
> > Frederic Valleur | LaMaison
> > >Hi guys,
> > >Sorry to hijack. Could someone just quickly explain what a CVEX shader
> > is?
> > >Not heard of this before. I take it it's different from a VEX shader? Is
> > >is a compiled version? What situations would you use it for?
> > >Thanks
> > >Andy
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> Un saludo
> Best Regards
> Pablo Giménez
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