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

Jose Pedro Canilho jpc_ace at hotmail.com
Mon Jul 2 09:24:43 PDT 2018

Hi Laurens.
Thank you for your reply!

I've actually already had a black background color set in my camera ("setClearColor( 0,0,0,1 )").

I've tried your rendering hint solution, but unfortunately it didn't solve my problem. Do I need to call any state set updating function after setting the rendering hint?

I've also double checked for the correct format in pretty much any place I can think of. I've checked that my raw images are indeed 8bit RGBA. When I construct my osg::image, I use the following:

osg::ref_ptr<osg::Image> img = new osg::Image();

I believe these format options are correct, since I'm able to create other RGBA images correctly.

Thanks once again.


From: osg-users <osg-users-bounces at lists.openscenegraph.org> on behalf of L. Voerman <l.voerman at rug.nl>
Sent: Monday, July 2, 2018 3:13 PM
To: OpenSceneGraph Users
Subject: Re: [osg-users] Drawing a partially transparent image in a quad

Hi Jose,
You may have a black background, with the blending actually (partly) working, change
getCamera()->setClearColor( osg::Vec4(r,g,b,a) );
to see if that's the case.
the stuff that needs blending needs to be rendered after the background, normally done with:

If it's not blending at all I would recommend you to check if your image did not end up as an RGB image instead of RGBA.
Regards, Laurens.

On Mon, Jul 2, 2018 at 11:28 AM Jose Pedro Canilho <jpc_ace at hotmail.com<mailto:jpc_ace at hotmail.com>> wrote:

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.

osg-users mailing list
osg-users at lists.openscenegraph.org<mailto:osg-users at lists.openscenegraph.org>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.openscenegraph.org/pipermail/osg-users-openscenegraph.org/attachments/20180702/9faaba57/attachment.html>

More information about the osg-users mailing list