Re: massive hair instance render

["Bernard Lebel" <3dbernard(at)gmail.com>]

Gods of mental ray, correct me if I'm wrong.........


Just to be pedantically clear about what does the hair BSP:

The geometry generated by hair is part of the "main" BSP tree and changing the hair generation settings like number of hairs and strand multiplier will affect the "main" BSP tree, as this will affect the number of triangles in the scene. You can verify that by doing diagnostic renders:

Application.CreatePrim("Sphere", "MeshSurface", "", "")
Application.DeleteObj("sphere")
Application.CreatePrim("Cylinder", "MeshSurface", "", "")
Application.SetValue("cylinder.cylinder.radius", 2.39, "")
Application.SetValue("cylinder.cylinder.height", 40, "")
Application.SetValue("cylinder.polymsh.geom.subdivu", 24, "")
Application.SetValue("cylinder.polymsh.geom.subdivv
", 24, "")
Application.SetValue("cylinder.polymsh.geom.subdivbase", 24, "")
Application.SetValue("cylinder.polymsh.geom.subdivbase", 24, "")
Application.SetValue("cylinder.polymsh.geom.subdivv", 24, "")
Application.SetValue("cylinder.polymsh.geom.subdivv", 48, "")
Application.FreezeObj("", "", "")
Application.Rotate("", 0, 0, 90, "siRelative", "siLocal", "siObj", "siXYZ", "", "", "", "", "", "", "", 0, "")
Application.FreezeObj("", "", "")
Application.ActivateObjectSelTool("")
Application.DeselectAll
()
Application.ActivateObjectSelTool("")
Application.CreatePrim("Sphere", "MeshSurface", "", "")
Application.Translate
("", 0, 0, -7.84688268062173, "siRelative", "siLocal", "siObj", "siXYZ", "", "", "", "", "", "", "", "", "", 0, "")
Application.Translate("", 0, 0, 0.721777065527067, "siRelative", "siLocal", "siObj", "siXYZ", "", "", "", "", "", "", "", "", "", 0, "")
Application.ApplyHairOp("sphere", "")
Application.InspectObj("ViewRenderOptions", "", "", 1, "")
Application.SetValue
("ViewRenderOptions.DiagnosticPhoton", 0, "")
Application.SetValue("ViewRenderOptions.DiagnosticGrid
", 0, "")
Application.SetValue("ViewRenderOptions.DiagnosticGrid", 0, "")
Application.SetValue("ViewRenderOptions.DiagnosticBspTreeDepth", 1, "")

Draw a render region

Set the strand multiplier to 0, render
Set the strand multiplier to 2, render
Set the total hairs to 13,000, render

Unless there are shaders being used that modify the hair geometry on-the-fly or other characteristics of hair, changing the hair BSP should not affect actual render time (when buckets are being rendered).

The hair BSP deals with the pre-processing phase, that is, the generation of hair geometry. The aim at the hair BSP tree is not to speed up ray intersection, but to speed up things like surface collisions and similar things that require the renderer to know where the geometry is in space to generate accurately the hair geometry. So changing the hair BSP should affect the hair generation time only (if, like I said, there is nothing that modifies that geometry or else during rendering).

Ultimately the hair BSP will affect the "overall" render time, because the rendering doesn't happen without the pre-processing of hair.




Bernard




On 5/30/07, Kim Aldis <
XSI(at)kim-aldis.co.uk> wrote:
> I'm not sure if this also applies to instancing but hair has its own BSP
> settings. Normal hair renders that can make a huge difference.
> 
> > -----Original Message-----
> > From: owner-xsi(at)Softimage.COM [mailto:owner-xsi(at)Softimage.COM] On
> > Behalf Of Bernard Lebel
> > Sent: 30 May 2007 01:27
> > To: XSI(at)Softimage.COM
> > Subject: Re: massive hair instance render
> >
> > Definitely consider using dynamic bsp and lower the mesh splitting
> > factor (try 0.5, then 0.2, then 0.1...). Will make rendering slower,
> > but will render. Also, definitely consider using the rasterizer, if it
> > doesn't change too much your lighting.
> >
> >
> > Cheers
> > Bernard
> >
> >
> >
> >
> > On 5/29/07, Kris Rivel <krisrivel(at)gmail.com> wrote:
> > > I'm building a tree with many extremely photo-realistic leaves on it.
> > > I'm using some SSS shading which looks great but together with
> > massive
> > > leaf instance count, my renders are hitting the roof.  I'm trying to
> > > stick to a 2GB memory limit too which is all thats available on the
> > farm
> > > I will be using.  Just curious if anyone has any tips for handling
> > such
> > > massive hair instance renders.  I still have a lot of tweaking and
> > > optimization to fiddle with but it would be great to know of any
> > other
> > > nice tricks up front that I may not have thought about.  Thanks.
> > >
> > > Kris
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