Thanks Sebastian, I have in fact looked through every geometry shader tutorial I could find and have tried to implement a simple pass-through sahder identical to the one you posted, but when I add the geometry shader I just get a black screen with no OpenGL error messages, and if I remove the geometry shader and keep the vertex and frag shaders I get my normal scene. I'm not sure if maybe I'm missing passing through texture coordinates or something of that nature...?
-Ethan SMesserschmidt wrote: > Hi Ethan, > > > > > Thanks, that makes sense that it would just be rendering a quad and that > > the original scene geometry would be lost. However, the GLSL geometry > > shader only accepts primitives of the type point, line, or triangle->is it > > perhaps rendering two triangles to the geometry shader to make up the quad? > > How would I even go about determining since there's no debugging available? > > > > But back to what I'm trying to do, I'm trying to use a geometry shader to > > calculate the min, max, mean, std dev, and histogram of an RTT texture. > > Fellow osg forum member Aurelius has advised me that he has working code > > that does this using geometry shaders and pointed me to: > > http://http.developer.nvidia.com/GPUGems3/gpugems3_ch41.html > > and > > > This seems rather complicated for a starter. Also it requires feedback > buffers which I never got working in OSG, so there might be some more > obstacles here. > > > http://developer.amd.com/wordpress/media/2012/10/GPUHistogramGeneration_I3D07.pdf > > but the first example only has Cg code and not GLSL, and the second example > > is a paper that describers an algorithm but doesn't have any src. These > > are both potentially great resources, but I'm struggling to just get a > > basic pass-through geometry shader working to get some sort of starting > > point. > > > Geometry shaders are really simple. You simply need to know your input > primitives. > A very basic geometry shader looks like this: > > > #version 400 > layout(triangles) in; //we receive triangles > layout(triangle_strip, max_vertices = 3) out; > > void main() > { > for (int i = 0; i < 3; ++i) > { > > vertex = gl_in[i].gl_Position; > gl_Position = vertex; > EmitVertex(); > } > > EndPrimitive(); > } > > But seriously, there are examples in OSG touching geometry shaders and > there are plenty of tutorials about glsl and shaders. > > cheers > Sebastian > > > > > As a side note, I am also considering using a compute shader since this > > would be the more natual fit for this type of algorithm while the geometry > > shader method is more of a "hack" that goes against the original intention > > of the geometry shader, but I'd be happy using either method, I'm just > > trying to get some traction on either of them. > > > > -Ethan > > > > > > SMesserschmidt wrote: > > > > > Am 18.11.2013 15:32, schrieb Ethan Fahy: > > > > > > > > > > Hello, > > > > > > > > Preface: I realize this question comes about because I've never really > > > > learned OpenGL/GLSL from the ground up and am likely missing some > > > > simple concepts, but I mostly have been coasting by at the osg > > > > middleware level and have been doing OK so far. > > > > > > > > If I want to do some simple post-processing I can create a > > > > render-to-texture camera and render to the framebuffer. I can attach a > > > > texture to the framebuffer and then create another "screen" camera to > > > > render that texture to the screen. I can add a GLSL shader program to > > > > this texture so that before the texture gets rendered to the screen it > > > > gets an effect added to it using the shaders. > > > > > > > > When I use shaders attached to 3-D model nodes in the scene itself, the > > > > meaning of the vertex and frag shaders is easy to understand->the > > > > vertices of the 3-D model are the vertices referenced in the vertex > > > > shader. However, When I render my scene to a texture and then do a > > > > simple pass-through vertex and frag shader combo, what is the meaning > > > > of the vertices in this scenario? I had assumed that once you render > > > > your scene to a texture, all knowledge of the original scene's geometry > > > > and vertex locations has been lost, is this true? If so, then what > > > > vertices am I dealing with? It's easy enough to follow along with > > > > examples and to use a simple pass-through vertex shader, but I'd like > > > > to understand this better because I now want to insert a geometry > > > > shader in between the vertex and frag shaders and again I'm not sure > > > > whether to use point, line, or triangle in my geometry shader as the > > > > primitive type because I thought that the geometry and primitives of > > > > the original scene wou > > > > > > > > > ld > > > > > b > > > > > > > > > > e lost after rendering to texture. > > > > > > > > > > > Usually when doing the post-processing pass you will be rendering to a > > > fullscreen quad. So the vertices you are dealing with are those of the > > > quad you are rendering too. > > > And yes, If you don't any further actions, rendering to texture will not > > > preserve the information on your orignal vertices etc. > > > The question is what you want to achieve. A geometry shader inbetween > > > your postprocessing pass will work on the quads vertices. > > > Maybe you should elaborate which kind of post processing you want to > > > achieve, so we can help you here. > > > > > > > > > > What am I missing here? Any clarification is most welcome. > > > > > > > > -Ethan > > > > > > > > ------------------ > > > > Read this topic online here: > > > > http://forum.openscenegraph.org/viewtopic.php?p=57281#57281 > > > > > > > > > > > > > > > > > > > > > > > > _______________________________________________ > > > > osg-users mailing list > > > > > > > > http://lists.openscenegraph.org/listinfo.cgi/osg-users-openscenegraph.org > > > > > > > > > > > > > > _______________________________________________ > > > osg-users mailing list > > > > > > 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=57285#57285 > > > > > > > > > > > > _______________________________________________ > > osg-users mailing list > > > > http://lists.openscenegraph.org/listinfo.cgi/osg-users-openscenegraph.org > > > > > _______________________________________________ > osg-users mailing list > > 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=57298#57298 _______________________________________________ osg-users mailing list [email protected] http://lists.openscenegraph.org/listinfo.cgi/osg-users-openscenegraph.org
