I am having a terrible time trying to use an ogre material to place a simple grass texture onto my landscape.

I've seen a post about how to do this for CubicVoxels but I am using the marching cubes algorithm and the smooth extractor.

Apparently all I need to do is use the same position coordinates for the texture coordinates as seen on this post.

http://89.151.96.106/forums/viewtopic.php?f=2&t=28452



I haven't found it dead easy... This seems to be easy in c++ code, but apparently it is much more efficient to put this conversion in a shader so that the GPU handles it.

Does anyone have any experience with Ogre Materials and shaders that can give me some pointers on applying textures to polyvox meshes?

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--Real Programmers use a magnetized needle and a steady hand.
--xkcd--

You don't actually need to do anything in the vertex shader - the key point is that in the fragment shader you shoud already have the world space position and you can use this directly as a texture coordinate. E.g to project a texture along the XY plane you can do something like (psuedocode):



So you don't actually pass texture coordinates to the GPU, you simply use the world space posiition as if it actually was texture coordinates. In practice, you probably want to scale, e.g:



Will make the texture repeat every 100 voxels.

This is going to sound a little noObish... but I don't entirely see how to use this with Ogre. I know Ogre has fragment shaders to go along with the material, but isn't the texture applied in the '.material' file?

Also you mentioned worldspace coordinates. I'm so new at shaders I have no idea how the shader even gets these coordinates. I assume its the positional coordinates I retrieve from polyvox, but I am not sure.

Your code makes sense, I just seem to be missing a couple key pieces of understanding in order to apply it.

_________________
--Real Programmers use a magnetized needle and a steady hand.
--xkcd--

It sounds like you might need to brush up on shaders then, before you try anything too fancy with PolyVox. You can even use something really simple like Ogre's sphere prefab. Even using just a sphere you can learn how the texturing and lighting pipeline works, and even try techniques such as triplanar texturing which you will probably want for the terrain.

Very true. I have alot to learn in order to use shaders appropriately. For now I am just trying to get an ugly texture on so i can see the 3d details of my terrain. It shouldn't be anything fancy. I just don't know how to get the polyvox coordinates used as texture coordinates. How do I pass them in?

I'll keep trying to find a semi beginners friendly guide to shaders. Maybe I can figure it out. Anyone know any good guides to shaders?

_________________
--Real Programmers use a magnetized needle and a steady hand.
--xkcd--

If you want to get by without shaders then you can probably make use of the ManualObject::textureCoord() function. Using this you can probably apply a texture projected along a single axis but you won't be able to do anything fancy like triplanar texturing.

If you do want to use shaders (and ultimatly you will) then it is beyond what I can explain here. You can't mix shaders with the fixed function pipeline, so when you start using shaders for texturing you also have to implement your own lighting and the projection of vertices from local to world to clip space.



The Cg Tutorial is a prety comprehensive book which should get you started if you want to use Cg. You'll also need to deal with Ogre specific stuff such as setting up your material scripts, but I don't know what to look at there beyond the Ogre manual.

So I have been studying alot about shaders and I'm making some progress.
My texture shader is still not working, but I have made some very simple shaders that work.

I had, what I hope is, a simple question.

These worldspace coordinates. Are they just the Positional coordinates? or do I need to multiply the position by the ogre world_matrix?

I believe multiplying the position in by the world_matrix will give me the world space coordinates but I am not sure.

Thanks for the help and patience.

_________________
--Real Programmers use a magnetized needle and a steady hand.
--xkcd--

You may want to read up a little bit on the fundamentals of how 2D images of 3D objects are displayed on the screen. A good place to do this can be found here:

http://glprogramming.com/red/chapter03.html

Once you have a grasp of that you can get the picture of how it's done in the modern GPU scheme of things.

http://developer.nvidia.com/node/76 (section 1.2.3)

So basically when you render an object, they started in model space (local space, etc). A world matrix (for example) would transform your objects into a common space, usually called world-space, a space where they co-exist. From there it's a series of further transformations until finally you reach screen space, which is a coordinate system that maps directly to your 2D screen. Read the first link, it's all there.

In a programmable shaders you have to do all the transformations. Before this in the fixed function pipeline the implication was it was done for you, you would just issue state change commands on the CPU (in OpenGL it's just enter some GL_MATRIX state, do the transforms by invoking the transform functions).

Refer to Ogre's shader (material section) section on how to do this in Ogre. Basically you just have to define materials scripts and bind auto parameters and also declare them in your shaders.

I'm so close. All I am seeing is a flat square that is slightly off-white due to 80% ambient light, but no texture. As far as I know the code is so close. I just don't know what my mistake is. I'm guessing my parameters are wrong.

Here is the material file.



Here is the cg file.



The vertex shader is not being used currently.

So am I messing up a parameter or miscalculating the world space?

_________________
--Real Programmers use a magnetized needle and a steady hand.
--xkcd--

I can't write much as i'm posting from my phone, but the key point here is that the transform must be done in the vertex shader. You can't do it in the fragment shader. I.e. the first line of your fragment shader needs to be moved to the vertex shader. There are probably more mistakes, i'll try to help more when i'm at my pc.