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 would
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
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