TX_SELECT for Performer or OpenGL?

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Stephen Maher (maher++at++holodeck.gsfc.nasa.gov)
Tue, 29 Sep 1998 13:02:53 -0400 (EDT)

I had no responses to this in comp.sys.sgi.graphics and
comp.graphics.api.opengl. I actually need to do this in Performer, so I
thought I'd ask here ...

> On an SGI IR in OpenGL, I need to clamp textures such that no pixels are
drawn which fall outside the 0.0 to 1.0 texture coordinate range -
essentially the same as what TX_SELECT did in IrisGL.

Using glTexParameter, a GL_TEXTURE_WRAP value of
GL_CLAMP_TO_BORDER_SGIS, with GL_TEXTURE_BORDER_COLOR set to x00000000
(e.g., zero alpha) would probably do what I need, but texture borders
aren't available on IRs.

Setting the outside pixels of the texture to zero alpha would work, but
is problematic in our case because we want to be able to do this
dynamically (programmatically), which is fine for standard textures, but
we also need to support clipmapped textures (where getting into the
texture and changing the edge pixels on the fly is not practical,
AFAIK).

I've thought about stencil buffers, etc., to mask the area I *don't want
drawn, but haven't come up with anything.

Any tips?

Thanks,
Steve

--
stephen.maher++at++gsfc.nasa.gov (301) 286-3368  fax:(301) 286-1776
http://holodeck.gsfc.nasa.gov/vr/vr.html
NASA Goddard Space Flight Center

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