3D textures / texture array questions

FYI the difference between 3D textures and the new texture array are as follow off the top of my head.

3D textures
Supported on older hardware.
Filtering will take place between layers.

Texture arrays
Only Geforce 8 series and newer aka DX10 hardware
Filtering isn't done between layers.
You can use them with FBOs

Your 3rd option is use a texture atlas. This gives you all your textures in 1 2d Texture, and can be used on all hardware that has a fragment shader. Only issue is filtering can be a headache, unless you have borders around you textures or limit it to point sampling.

Unless you use .dds files, which I think have texture array support and 3d texture support, you will have to load each 2d texture into memory

e.g.
unsigned char[w][h][d][channels]; array

and then upload that to GL. I myself use PBO to make it a tad bit faster, but since I am targeting DX10 hardware its ok to assume PBO will be there.

Be warned I have 16 textures in a texture array and it still kills performance on my terrain, as you still have to access the texture sampler 16x...

Now I've implemented 3D textures, just by loading each slice apart. Well, it works. It would be nice if there was options to use already loaded 2D textures. But I guess I'll have to setup a FBO for that, and render the 2D textures on quads into the 3D/Array Texture. That's not worth the effort for me now.

Filtering between the layers is indeed not needed here. I'm not targeting for old hardware, because *IF* my stuff will ever release, we live in the year 2059. Do array's have any other benefit over 3D textures (performance)?

BTW, 3D textures can also be used for FBO's as well. I use them alot for probes :)

Thanks for the tips!
Rick

Well if you want to just use glGetTexImage and grab the imageData, and upload that data back into a 3D texture... I don't know why you would do this? Is this data created after the app is running? Otherwise I can't see why you just don't load the textures into the 3D texture vs. a 2D texture.

So glGetTexImage was the command I was looking for... thanks! Textures used in a set (3D texture in this case) are often also loaded as a normal 2D texture for other purposes in my case. So I thought maybe it was faster to load them from an existing source. But I'm not sure if its really faster than just loading it from the hard-drive.

Rick