Jason Beverage wrote:
Hi all,
I'm trying to figure out a way to modify layer opacity using
TexEnvCombine that takes into account the underlying alpha channel of
a texture.
Do you mean if unit 1's texture has transparency, you want that to show
through to unit 0's texture?
The osgFX::MultiTextureControl does very close to what I'm looking to
do, but doesn't take into account the fact that the underlying texture
may contain transparency (like a road overlay).
From my understanding of texenvcombine, I can either use a constant
color or SRC_ALPHA as an operand, but not a combination of both.
It sounds like you need three parameters combined (2 texture colors and
a user-defined parameter), so your only hope is the INTERPOLATE mode for
the alpha values (INTERPOLATE is the only combiner operation that takes
three parameters). Try this:
tec->setSource0_RGB(osg::TexEnvCombine::TEXTURE0);
tec->setSource1_RGB(osg::TexEnvCombine::TEXTURE1);
tec->setCombine_RGB(osg::TexEnvCombine::MODULATE);
tec->setConstantColor(osg::Vec4(1.0, 1.0, 1.0, userDefinedAlpha));
tec->setSource0_Alpha(osg::TexEnvCombine::TEXTURE0);
tec->setSource1_Alpha(osg::TexEnvCombine::TEXTURE1);
tec->setSource2_Alpha(osg::TexEnvCombine::CONSTANT);
tec->setCombine_Alpha(osg::TexEnvCombine::INTERPOLATE);
I just made this up, so I have no idea if it will work or not. It might
not be the only possibility, either, but it's all I can think of right now.
--"J"
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