Ran Yakir (rany++at++bvr.co.il)
Wed, 1 Nov 1995 07:44:59 +0000
>From the results I get on my IMPACT, both OpenGL and IrisGL load 4 bits/comp
textures. Moreover, the bilinear filter seems to do its calculations in 4 bits
only, therefore creating a very noticable quantization effect when zooming into
a texture.
Bruce,
Do you use very large textures (1024x1024 for example) ? I was running an
IrisGL (non-Performer) program on that IMPACT, with a database that uses 4 such
textures. The textures were not drawn. When I zoomed them down to 512x512 each,
everything was fine. When you come to think of it, it makes sense that such
large textures will pose a problem : a 512x512 texture will occupy a space of
about 680K bytes in texture memory (2 bytes per texel, and mipmaped). A
1024x1024 texture will need a space of 2.7 Mbytes (more than 1M on the High
IMPACT). Sure, you can swap textures on the IMPACT, but what happents if one
texture is too large ?
On the RealityEngine, mipmaped 1024x1024 textures are scaled down to 1024x512.
Ran
> On the memory usage front:
>
> I've noticed that when loading flight format files into performer 2.0 on
> High IMPACT + TRAM option the Iris GL implementation seems to use 8 bits
> per component but the Open GL implementation uses 4 bits per component
> (eye balling). 5 bits per component internal on ONYX would use less
> memory, it depends what your loader is doing.
> Also a mipmapped minifacation filter would use more texture memory than
> one without mipmaps, although possibly a smidgen less than you are seeing.
> Could this be some minification filter default issue?
>
> Just a couple of wild guesses.
>
> Rgds,
> Angus.
>
> On Oct 31, 5:23pm, bmcquear++at++dw3f.ess.harris.com wrote:
> > Subject: Textures
> >
> > Hi,
> >
> > We recently accquired an Impact (High AA Impact / TRAM Option Card) and
> > are trying to run an application that previously ran on an Onyx, and
> > Indigo 2 Extreme.
> >
> > Our application is implemeted in Performer 2.0, but linked with Iris GL
> > (temporarily). The problem is that I'm trying to read in a large
> > textured database (dwb format), and the texture is not being loaded in.
> > One strange thing is that I can telnet to the Impact from an Indy, run
> > the application, and all the textures are loaded and displayed.
> >
> > I also tried to load the application with perfly on the Impact, but
> > again the textures were not displayed. The output from notify indicates
> > that the total texture use goes above 100% of the RM (for example
> > "Total Texture Use = 137 % of 4 MB Raster Manager" ).
> >
> > Any ideas or explanations would be greatly appreciated.
> >
> > Thanks,
> > Bruce McQueary
> >
--
__ | Ran Yakir
/_) _ __ \ / _ / o __ | Graphics App. Chief Engineer
/ )_ (_(_) ) \/ (_(_/<_(_)( | BVR Technologies Ltd.
_/ |
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