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Texturing large terrain

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I am rendering large terrain (65km x 65km) at 8m height resolution and 1m triangle resolution by sampling height with bi-cubic interpolation. I've been experimenting but having trouble finding a decent method of texturing. The texturing needs to be detailed at ground level and look good from far away as well (no view distance culling, entire terrain is visible).

Methods that I've tried but look bad:

[b]Splat mapping[/b] - Textures that are detailed at ground level (about 1m x 1m) tile very obviously.
[b]Macro texture + detail textures[/b] - Can't really afford to have a decent resolution macro texture for the entire terrain. Looks good from far away but gets pretty bad as you get close.

Methods that look nice but not technically possible for me:

[b]Per-tile procedural on GPU[/b] (see Outerra) - Can't afford the render-to-texture overhead for when terrain tiles are split.

Currently I'm leaning toward trying a larger scale splat map (say 1024m x 1024m textures) to avoid tiling and add detail textures on that. However, I don't really like the look of a stretched macro texture with a detail texture on it (looks very dated).

Are there any techniques that I haven't considered? I don't need fine control over textures so procedural approaches are fine. But it will need to include dirt/grass/sand/rock based on slope/altitude. All ideas are welcome. Edited by colinhect

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Thanks for the input.

The main advantage of megatextures is that you can keep a small portion of a very large virtual texture on the GPU at a given time. While this would solve the tiling issues it would be nearly impossible to hand-paint 65km x 65km at a decent resolution. And if it wasn't hand-painted then it might as well be procedural per-tile on the GPU at runtime (no disk-space usage). To have 1 pixel per ~0.4 cm (decent texture resolution) would be 768 terabytes as 24bit uncompressed. So I don't think megatextures would work on this scale. Edited by colinhect

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Google: Texture Mipmap Quadtree

You may find this to be a good read: [url="http://www.realityprime.com/articles/how-google-earth-really-works"]http://www.realityprime.com/articles/how-google-earth-really-works[/url] Edited by UltimaX

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Why do you need to texture the terrain, you could just color it according to something like vertex height from sea level. You could also add some modifiers like this area is dirt and this grass. Then you place all your rocks, grass, pushes, trees on top of the terrain. Though i am not sure how it would look, because i have not implemented large terrain like that yet, but been playing with the idea quite much in my head and done quite much calculations, but realized that I can not create map of earth at 1 x 1 meter triangle resolution, even if the client would not need to load all of it at once, but the server would.

Anyway at that scale you will run out of memory quite fast if you want to texture the whole terrain at once.

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Thanks for the replies.

[quote name='UltimaX' timestamp='1342546768' post='4960080'] Google: Texture Mipmap Quadtree You may find this to be a good read: [url="http://www.realityprime.com/articles/how-google-earth-really-works"]http://www.realityprime.com/articles/how-google-earth-really-works[/url] [/quote]

After a quick skim this seems like a similar idea as mega texturing. The problem is that I can't have a large virtual texture because it would be too large to hand-paint/generate and store on disk. This is why I'm looking more at procedural splatting methods.

[quote name='TMKCodes' timestamp='1342546778' post='4960081'] Why do you need to texture the terrain, you could just color it according to something like vertex height from sea level. You could also add some modifiers like this area is dirt and this grass. Then you place all your rocks, grass, pushes, trees on top of the terrain. Though i am not sure how it would look, because i have not implemented large terrain like that yet, but been playing with the idea quite much in my head and done quite much calculations, but realized that I can not create map of earth at 1 x 1 meter triangle resolution, even if the client would not need to load all of it at once, but the server would. [/quote]

This would not be acceptable. I could have much better results by just selecting the texture in a pixel shader based on height/slope with some added noise (see [url="http://www.gamedev.net/blog/73/entry-1692117-terrain-texturing-explained/"]here[/url]). But that method isn't desirable because the textures will still tile noticeably and the sharp edges between textures doesn't look very good. Also, there is noticeable popping between terrain LOD levels.

[quote name='TMKCodes' timestamp='1342546778' post='4960081'] Anyway at that scale you will run out of memory quite fast if you want to texture the whole terrain at once. [/quote]

I'm not looking to have a unique pixel for every centimeter of the map. I'm looking for some sort of procedural technique of texturing the terrain in a way that tiling is not obvious and can look good from near and far.

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[quote name='colinhect' timestamp='1342549792' post='4960099']

After a quick skim this seems like a similar idea as mega texturing. The problem is that I can't have a large virtual texture because it would be too large to hand-paint/generate and store on disk. This is why I'm looking more at procedural splatting methods.
[/quote]
Mega/virtual texturing doesn't mean that everything must be hand painted.
You just create the data in whatever way you want instead of just loading it off disk. (splatting, procedural textures, baking GI data just in time.. etc.)

Battlefield 3 used splatting with virtual texturing quite nicely.
http://publications.dice.se/attachments/GDC12_Terrain_in_Battlefield3.pdf

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[quote name='Pottuvoi' timestamp='1342553391' post='4960140']
[quote name='colinhect' timestamp='1342549792' post='4960099']
After a quick skim this seems like a similar idea as mega texturing. The problem is that I can't have a large virtual texture because it would be too large to hand-paint/generate and store on disk. This is why I'm looking more at procedural splatting methods.
[/quote]
Mega/virtual texturing doesn't mean that everything must be hand painted.
You just create the data in whatever way you want instead of just loading it off disk. (splatting, procedural textures, baking GI data just in time.. etc.)

Battlefield 3 used splatting with virtual texturing quite nicely.
[url="http://publications.dice.se/attachments/GDC12_Terrain_in_Battlefield3.pdf"]http://publications....attlefield3.pdf[/url]
[/quote]

Thanks for the reply. This is a great read and may be relevant to my project.

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Hmm, my thought would be that you have 2 or more textures for each height/slope combination that you want. Then generate 2D simplex noise based on the map co-ordinates and use it as a blend map for the x different textures. It's a bit of shader work and wouldn't give 100% unique appearance, but hopefully enough to break up the tiled look.

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