[osg-users] ClipNode Opposite Behavior

[Christian Buchner]

If you want the hole to be specified in object local coordinates, use
gl_Vertex.
Getting world coordinates is a bit more tricky, you would need to have the
transformation matrix between object coordinates and world coordinates
accessible
in the vertex (or fragment) shader.

Definitely do not use gl_FragCoord - because this one is in 2D screen space.

Christian



2015-07-26 15:46 GMT+02:00 Glenn Waldron <gwaldron at gmail.com>:

> Erick,
> gl_FragCoord is almost certainly not what you want (Google it). Try
> something like this:
>
> Vertex shader:
>
> uniform vec3 center;
> varying float dist;
> void main()
> {
>     vec4 vertex = gl_ModelViewMatrix * gl_Vertex;
>     dist = length(center - vertex.xyz);
> }
>
> Fragment shader:
>
> uniform float rad;
> varying float dist;
> void main()
> {
>     if ( rad < dist )
>         discard;
>     else
>         gl_FragColor = ...;
> }
>
>
>
> Glenn Waldron / @glennwaldron
>
> On Fri, Jul 24, 2015 at 9:22 AM, Erik Hensens <ehensens at hunter.com> wrote:
>
>> Thanks Christian. It's funny you mention that because since I'm not
>> setting the color, the quad looks like an old television tuned to a
>> frequency not in service, i.e. "static" or "snow". I think every time the
>> quad is rendered each fragment's color is set to whatever value is in some
>> uninitialized portion of memory, and each fragment changes color each time
>> it is rendered. Quite a funny effect!
>>
>> I added the following line to set the color, and now it is always blue,
>> but it's still not putting a hole in my quad, it's all there or all gone
>> depending on whether I say if (fDist < rad) or if (fDist > rad):
>>
>>
>> Code:
>>
>> // The fragment shader program source code
>> std::string szFragSource(
>> "uniform vec3 center;\n"
>> "uniform float rad;\n"
>> "void main()\n"
>> "{\n"
>> "float fDistX = gl_FragCoord.x - center.x;\n"
>> "float fDistY = gl_FragCoord.y - center.y;\n"
>> "float fDistZ = gl_FragCoord.z - center.z;\n"
>> "float fDist = sqrt(fDistX * fDistX + fDistY * fDistY + fDistZ *
>> fDistZ);\n"
>> "gl_FragColor = vec4(0.0,0.0,1.0,1.0);\n"
>> "if (fDist < rad) discard;\n"
>> "}\n"
>> );
>>
>>
>>
>>
>> Any other ideas about why my code doesn't achieve what I want? For
>> example, am I using gl_FragCoord correctly? Are there other errors in my
>> frag source?
>>
>> Thanks again!
>>
>>
>> cbuchner1 wrote:
>> > I believe your fragment shader is not setting the output fragment color
>> at all, which is a minimum requirement for a fragment shader to work.
>> >
>> >
>> > Christian
>> >
>> >
>> >
>> > 2015-07-23 23:59 GMT+02:00 Erik Hensens < ()>:
>> >
>> > > Sorry for the triplicate post, I received an error message on trying
>> to post until I removed the quotes...
>> > >
>> > > ------------------
>> > > Read this topic online here:
>> > > http://forum.openscenegraph.org/viewtopic.php?p=64458#64458 (
>> http://forum.openscenegraph.org/viewtopic.php?p=64458#64458)
>> > >
>> > >
>> > >
>> > >
>> > >
>> > > _______________________________________________
>> > > osg-users mailing list
>> > >  ()
>> > >
>> http://lists.openscenegraph.org/listinfo.cgi/osg-users-openscenegraph.org
>> (
>> http://lists.openscenegraph.org/listinfo.cgi/osg-users-openscenegraph.org
>> )
>> > >
>> > >
>> > >
>> >
>> >
>> >  ------------------
>> > Post generated by Mail2Forum
>>
>>
>> ------------------
>> Read this topic online here:
>> http://forum.openscenegraph.org/viewtopic.php?p=64467#64467
>>
>>
>>
>>
>>
>> _______________________________________________
>> osg-users mailing list
>> osg-users at lists.openscenegraph.org
>> http://lists.openscenegraph.org/listinfo.cgi/osg-users-openscenegraph.org
>>
>
>
> _______________________________________________
> osg-users mailing list
> osg-users at lists.openscenegraph.org
> http://lists.openscenegraph.org/listinfo.cgi/osg-users-openscenegraph.org
>
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.openscenegraph.org/pipermail/osg-users-openscenegraph.org/attachments/20150727/d43085b6/attachment-0003.htm>