I want a pixelshader to do lookups in an array of 256 textures. One of these textures will be updated each frame (the other 255 remaining unchanged).  I would prefer doing a lookup in a 3d texture, but a 3d texture cant be partially updated (updating it completely is not an option because of bandwidth).

To initialize the textures and samplers I would like to do:

texture texSlices[256];

sampler sliceSamplers[256];

for (int i = 0; i < 256; i++){
    sliceSamplers[i] = sampler_state
    {
        Texture = <texSlices[i]>;
    }
}

That does not work : it is complaning about the for loop. And even if it wasnt , this post says it wont work, and I have to outroll the loop.

Is there an other way to access a large amount of data, which changes partly every frame?


Edit: A sampler array is not a possibility : return tex2D(sliceSamplers[sliceIndex], uv); fails, because the arrayindex cant be a variable (....whose content cant be known at compile-time);

Are you sure about volume textures not doing partial updates? The docs imply that the LockBox-function records dirty regions. Sorry, I don't have much advice otherwise. Maybe tiling the data in a couple of large 2d-textures (depending on how much data it really is of course)?

/Jimmy

Thanks.
I have posted this in the wrong section I think. I thought because it was hlsl related, i'd put it in the direct3d section, but I am using xna. Your suggestion looks good, but I cant use native direct3d instructions in xna right?
The second suggestion (couple of large 2d-textures) would be too wastefull for my project: I would need to use setdata() on a large texture, while I only really want to update a part of it.

try the setpixel function although thats also most likely not what you want to do.

The Texture3D class in XNA have an overload (of SetData) for passing the dimensions of the "sub-box" you want to update. I would assume/hope the underlying D3D method is called.

/Jimmy

Thanks! that worked (using setdata() on part of a texture3d).
The data I want to put in the texture3d is generated in hlsl, so it would be better if I could render to a slice of a rendertarget3d directly, and then use gettexture(). But a rendertarget3d does not exist, and a rendertargetcube only has 6 slices.

So, if i understand correctly, the only way to fill a texture3d is by using setdata()?

Yes in D3D9 the only way as far as I know is to update using SetData / Lock. In D3D10 you can of course use a texture array, but since you were using XNA that is not an option.

How much data is it? If your card supports 8192x8192 2D textures, you can simulate a 512x512x256 volume texture (about 67Mb) with some pixel shader magic. Then it would be trivial to render to a selected 'slice' (just set the viewport). Of course this will be a lot less if there is only support for 4096 dimensions (256^3).

/Jimmy

It will be about as much data as my videocard can handle (512 MB ati 4870).
The simulated 3d texture on a 2d texture is a good idea; I think I will try it later on. I am using the "Color" surfaceformat without mips, so that would be 256 MB for 1 8k*8k texture, I think, which should be enough.
Thanks for all the help.