[osg-users] VPB/osgdem and transparent textures

Mike Lewis jhg886 at gmail.com
Wed Jul 2 11:19:23 PDT 2008


Hi Robert,

I admit one of the main reason I'm after blending / transparency in my
terrain is that I'm using source imagery that is reprojected from
geographic to UTM coordinates. The reprojection results in a slight
warping of the texture, leaving irregular NODATA bands around the
sides. When osgdem creates the terrain, these NODATA regions around
the border are colored opaque black. I'd like to, in essence, "slice"
off this black, NODATA border. I think VPB by default alpha's these
regions out, but this displays only when I add GL_BLEND to the
resulting .osg files.

Another, slightly less important reason for me wanting to have
transparency enabled on the terrain is that I'd like to make the
bodies of water on my terrain to have a very simple see-through or
reflection type of effect. I say simple because all it would take is
probably for the bodies of water to be transparent in the source
texture imagery.

As you can tell, I am still very new to OSG-- but willing to learn. I
really appreciate your response.

Mike

On Jul 2, 10:54 am, "Robert Osfield" <robert.osfi... at gmail.com> wrote:
> Hi Mike,
>
> It's a bit unusual to want to blend terrain, kinda suggests that the
> pipeline is being used inappropriately.  What exactly are you after by
> the alpha blending?
>
> Robert.
>
>
>
> On Wed, Jul 2, 2008 at 5:59 PM, Mike Lewis <jhg... at gmail.com> wrote:
> > Hi Robert,
>
> > Thank you for helping me. I actually just started using VPB / osgdem
> > so I can't say I'm familiar with all the concepts yet. I have only
> > been using osgviewer to view the .ive or .osg models that osgdem
> > generates. I was terribly wrong to say the alpha channel was being
> > ignored; If I go into all the .osg files for the database generated by
> > VPB, and add "GL_BLEND ON" to every geometry StateSet in the .osg
> > files, the model displays as desired in osgviewer.
>
> > I'm wondering if there is a simple way to tell vpb to generate the
> > database this way, instead of having to manually add them in?
>
> > Thanks,
> > Mike
>
> > On Jul 1, 12:57 pm, "Robert Osfield" <robert.osfi... at gmail.com> wrote:
> >> HiMike,
>
> >> What makes you think that the alpha is being ignored?  Have you
> >> enabled GL_BLEND in your app?
>
> >> Robert.
>
> >> On Tue, Jul 1, 2008 at 8:39 PM,MikeLewis<jhg... at gmail.com> wrote:
> >> > Hello,
>
> >> > I'm using OSG 2.4 and VPB 0.9.8 and I'm having an issue. I'm handing
> >> > osgdem raster texture files with transparency but the resulting
> >> > terrain models seem to ignore the alpha channels entirely. Also, I
> >> > thought VPB alpha'd out NODATA regions. For some reason, it seems to
> >> > be coloring them solid black instead, for me. Does VPB support having
> >> > transparency in the texture imagery? I've tried various PNG and
> >> > GeoTIFF images and seem to come upon the same result. I've tried the
> >> > various --RGBA and --default-color command line options to no avail.
> >> > Am I missing something?
>
> >> > Thanks
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