From: Colin Middleton (colin++at++sgi.com)
Date: 07/26/2004 04:47:39
Simon,
The best way I have found to generate rgba cliptextures with clipgen is to
generate a rgb cliptexture and a luminance cliptexture ( representing the
alpha values ) and then combine the two sets of raw imagery tiles to a
separate directory.
I usually edit the clipgen files ( .cp is the default filetype ) with a text
editor in order to get the same numbers. It is important to make sure that
the luminance cliptexture's .cp file is exactly the same as the rgb
cliptexture's .cp file apart from the texture formats at the top of the file
and the filenames of the textures you are loading.
The combination process sounds like a nightmare, but as cliptexture tiles
are all in a raw format and are the same image size, they are actually the
simplest files to read and process. As the two source .cp definition files
are almost the same the directory structure and filenames will be exactly
the same for both source cliptextures. So I can use a perl script to
recursivively descend the cliptexture tile directories and make sure that
all of the files are processed. This perl script calls a simple c program
that does the conversion either to rgba8 or rgba5551 from the two source
tiles.
All that's left after that is to make a .ct file that points to the
cliptexture imagery and then you have your rgba cliptexture.
As for the other issue with clipgen crashing I can't help you.
I hope this helps.
Colin.
___________________________________________
Colin Middleton,
SGI Professional Services,
1530 Arlington Business Park,
Theale, Reading, Berks. RG7 4SB.
United Kingdom.
Tel: +44 (0)118 9257692
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email: colin++at++sgi.com
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> -----Original Message-----
> From: owner-info-performer++at++performer.engr.sgi.com
> [mailto:owner-info-performer++at++performer.engr.sgi.com]On Behalf Of
> Simon.Mills++at++esa.int
> Sent: 26 July 2004 11:13
> To: info-performer++at++sgi.com
> Subject: [info-performer] Clipgen and alpha in cliptextures
>
>
> Hi Performers,
>
> I've encountered an unfortunate feature of the clipgen
> utility for creating
> cliptextures. I wanted to use the alpha component in a
> cliptexture as a
> "gloss map" to create a shiny sea effect in my applications.
> However, it
> appears that clipgen "applies" alpha values in source imagery
> into the RGB
> values in the produced cliptexture tiles. I can see this
> using for example
> the viewtile utility provided with Performer. Where alpha=0,
> RGB values are
> set to black. The intermediate pyramid files seem to be OK,
> only the raw
> tiles show this.
>
> Is this the desired behaviour? Anyway to stop it doing this?
> Any workaround
> (I guess I could bypass clipgen and do it manually but I would like to
> avoid that).
>
> Oh, yes, it's clipgen 1.2a8 (well, I think so, the help menu
> says 1.2a7).
> BTW, clipgen crashes on me without warning sometimes unless I
> restrict the
> number of processors it uses (I have a 6-CPU Onyx2). Any help
> on that one?
> Would a 64-bit version of clipgen help? Is there one available?
>
> Regards,
> Simon Mills
> Simulation & Modelling Section
> European Space Agency
> Noordwijk, The Netherlands
>
>
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