Hi,
On 11/04/11 23:03, Dan West wrote:
Thanks for the link JP. I didn't see anything drastically different
in what you were doing, so I started fiddling around with a bunch of
the different parameters that MAY have something to do with the
issue.
After no success there, I realized what I needed was an osg::TexEnv.
I created a TexEnv with the DECAL mode and the black background (that
should have been transparent) became transparent as I envisioned.
The table about halfway down this page
(http://www.opengl.org/sdk/docs/man/xhtml/glTexEnv.xml) helped me
understand what was happening. I'm not sure what 'TexEnv' is used if
one isn't set, but it appears the same as when a MODULATE TexEnv is
used. GL_MODULATE multiplies the existing and incoming alpha values,
losing the transparency (even though I would think the alpha would
stay at zero - zero times something is still zero, right??).
yes, osg defaults to modulate. I think modulate just multiplies the
colour vectors, it's not like blending equations.
Anyhow, you can try adding the following lines to the osgprerender
example if you're interested in what I was going for:
Code: osg::TexEnv* texenv = new osg::TexEnv( osg::TexEnv::DECAL );
stateset->setTextureAttributeAndModes( 1, texenv );
The only thing remaining that I'd like to do is to have the alpha
from newer texture renders 'darken' the existing alpha. If you
remember, I disabled clearing the color buffer, so I'd like my
overlay to darken if there are repeated passes over a particular area
of the texture (I'm only using solid colors, so it would look a bit
better than it would with the cessna 8) ).
Is this possible using the color buffer as I am, or would I have to
implement a shader to get this to work?
I'd recommend going the shader route. I've recently done some work on
projective texturing and the shader was much less effort than trying to
bend the fixed function pipeline to what I wanted.
rgds
jp
Thanks for the help guys! ~ talyn
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