NetNews Usenet Archive 1992 #30/NN_1992_30.iso/spool/comp/sys/sgi/18021

Internet Message Format | 1992-12-15 | 2.9 KB

Path: sparky!uunet!think.com!ames!sgi!fido!krypton!gavin
From: [e-mail] (Gavin Bell)
Newsgroups: comp.sys.sgi
Subject: Re: Inventor Question
Date: 15 Dec 1992 05:05:23 GMT
Organization: Silicon Graphics, Inc.  Mountain View, CA
Lines: 50
Message-ID: <[e-mail]>
References: <[e-mail]>
NNTP-Posting-Host: krypton.asd.sgi.com

In <[e-mail]> [e-mail] (ram rajagopalan) writes:
>Hi,
> I am trying to use Inventor to draw about 800 spheres.  I find the
> performance to be very slow.  I am not sure why this is happening.
> I am using transforms to position the sphere and scale the sphere
> and then creating the node sphere. All these are done under a
> separator node so that the transforms are not cumulated.
> My question is this.  Is there a better way of doing this to increase
> performance.  Thanks.
>Ram  Rajagopalan

Some things to try:

-- Put a complexity node at the top of your scene graph, and turn down
the complexity (its default is 0.5).  Inventor will then use fewer
polygons to render your spheres.

-- Make sure render caching is turned on at the separator node if you
aren't changing the sphere's transformations or geometry.  Viewers
turn on caching automatically, but if you know what parts of your
scene graph will change and what parts won't, you can do a better job
of it by turning caching on and off at particular separators.  Caching
is particularly important at node (like spheres) that calculate their
geometry on the fly; every time a sphere is traversed it recomputes
its geometry (turn on caching to get the geometry saved!).

-- It would be faster to 'flatten' your scene graph to pre-transform
all of the geometry and get rid of all of the transformations.  Every
transformation sends GL commands to manipulate the GL's transformation
matrix; the time used to do that could (potentially) be used to draw
polygons.  There is no easy way of doing this; with OpenGL's
non-editable display lists, OpenGL display lists should be
able to flatten out all of the GL transformation matrix commands
(Inventor doesn't do this for you).
  The fastest scene graph would have one SoIndexedTriangleMesh that
represented the polygons in all of your spheres, pre-transformed into
world space.  But eventually you will probably want to move or scale
just one sphere, or show all of the spheres bouncing around (if they
represent atoms in a chemical reaction or something...), or add new
spheres, and flattening everything into one IndexedTriangleMesh will
make those kinds of operations a lot harder.

-- Inventor relies on GL, so don't do things that cause the GL to
render things more slowly.  Don't turn on texturing, don't use
multiple light sources, don't use semi-transparent blended surfaces,
etc (unless of course you really need to and can live with the
performance hit).

--
--gavin     ([e-mail],  [phone])