As I began to reformulate my question, I think I found the answer.
If I were to run
osgsimple skydome.osg
I would see a skydome textured with skymap.jpg.
In osgsimple.cpp, there is no explicity loading of the texture and
mapping it to the sphere etc. Right? I assume this is done in the
model loader code. In looking in skydome.osg, I see that skymap.jpg is
specified as a texture to be used and that it appears to be assigned to
texture unit 0.
My question was basically this; If I have a bunch of osg files, each of
which have these embedded textures, then how do I know which texture
unit they reside in when I need to do a texture fetch in my shader.
It appears that the answer is that I will have to have information from
the osg file to know that.... In other words, I know that in the osg
file for a given model, Texture A is in texunit 0 and Texture B is in
texture unit 1 for example. Then in my app code I will need to use a
uniform to specify this. Is this correct?
Ed
Mike Weiblen wrote:
Hi Ed,
Not sure I'm following your question.
The app supplies the id of the texture unit and the tex coords as uniforms to
the shader. The shader code is responsible for using the sampler and texcoord
in a GLSL texture*() call, which retrieves the "texture data", then using that
texture data to achieve the desired result.
For example, in the OpenSceneGraph-Data distribution are a couple shaders that
use textures in different ways; the marble.frag shader uses a 3D noise texture
and a 1D sine lookup-table texture to generate a banded marble-like coloring. A
texture need not contain color data; the shader is free to determine how to use
any texture result to compute the gl_FragColor.
hth
-- mew
Ed wrote:
Ok... Here is another strange, and most likely stupid, question:
In the GLSL texture mapping examples I have seen, the texture is created
via the usual glGenTex*/glTex* functions. Then the object is rendered,
tex coords are specified, and the texunit is specified via a gluniform*
call which informs the shader which texture unit to use in the
texRECT/tex2D call.
Let's say I have a GLSL fragment shader. I enable the shader only when
running a particular object. How can i access the texture data from
within the shader? I am storing some non-visual data in the texture,
which is mapped to my objects, and using that data for various
calculations. If I have an OSG app, which uses a frag shader while
rendering a particular object, how do i retrieve the texture unit
information to perform the texRECT/tex2D?
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