[osg-users] Drawing a partially transparent image in a quad

Jose Pedro Canilho jpc_ace at hotmail.com
Mon Jul 2 02:28:13 PDT 2018

Hi everyone!

I've been battling with this issue for a couple of days and could really use some assistance. I'm fairly new to OSG (and 3D rendering in general) so I might be doing some rookie mistake.

In my program, I draw several quads, each containing a RGBA squared image.

At one point, I'm required to draw a new image on top of the existent images. This new image is also squared, but it is partially transparent (i.e., several pixels have the RGBA value of 0,0,0,0). At the moment, these pixels are being rendered black instead of transparent, and thus are mistakenly covering some regions of the background images/quads.

After quite a few searches online, I was pointed in the direction of the GL_BLEND macro and blend functions. I tried to enable blending for the new image/quad:

auto qss = quad->getOrCreateStateSet();
qss->setMode(GL_BLEND, osg::StateAttribute::ON)

but to no avail.

I also tried to attach a blend function to the quad, like such:

osg::BlendFunc* blendFunc = new osg::BlendFunc(osg::BlendFunc::SRC_ALPHA, osg::BlendFunc::ONE_MINUS_SRC_ALPHA );

but that didn't work either.

Are there any other issues that I might be overlooking here?

Thanks in advance.
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