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Hiyar

Terrain streaming

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I want to use multiple heightmap textures for rendering large terrain. I'm using vertex texture for terrain rendering, meaning my terrain size is limited by the maximum texture size supported by the hardware.(and also it is memory consuming to use one big texture). So if I want very large terrain, I need to implement some kind of terrain streaming. Questions: - The size of the heightmap tile textures? (large draw distance is still important) - What about terrain texturing. Each heightmap tile has it's own base texture and detail textures etc? - How is streaming and unloading data performed. Using a only distance criterion? - What are the pros and contras of streaming. - Links for papers about streaming. Thanks in advance. [Edited by - Hiyar on January 15, 2009 6:45:07 AM]

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What your looking for is something called mega texturing or in some instances geometry clipmapping (it's not technically the same thing but the idea is the same), its a method in where you use several large repeating textures where each one covers a larger area than the next.
the idea is that as you move across these textures you replace small areas of it just beyond your visibility limit, thus you always see a fresh set of textures.

1.size could be anything, rage from id software uses textures up to 20GB in size. However the size used in the GPU memory is always constant and whatever you say it is
2.texturing uses the same method, in fact it was originally made for this.
3.yes, distance and projected heading (if you can you should get ahead of yourself), unloading data is not needed, just replacing.
4. pros: it's seamless, has high resolution and you can have a unique texture all over the place.
Cons: it uses a lot of memory and if you move to fast across the map you will have problems updating it.
5. try google, but there isn't that much work done on this

Another method is something called texture paging or terrain paging or something like that, it is basically using several smaller textures and then rendering smaller patches of the mesh for each one.
It works pretty well, but you can often see the texture borders between them and if it's combined with LOD small gaps can occur.

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No, not mega texturing. Maybe you misunderstood my post. Thread is about geometry streaming, not only texturing. The heightmap texture is used for vertex texture fetching. XZ position values of the terrain are computed in the shader using scale bias etc, heightmap vertex textures is used in the shader for the terrain elevations.(Like displacement mapping) This approach saves memory, but like I said terrain size is limited by the maximum texture size. Because heightvalues are stored in the texture. I wanted to know how to use multiple heightmap (vertex)textures. And load them when need.

I'dont really want to implement streaming, but I want to know how it works for vertex texture based terrain.

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Well, as far as i know, there isn't that much of a difference between textures used for vertex texture fetch and "regular" textures. At least from the point of few of the application (i.e. the only real difference are in the shaders). So any method that allowes your application to stream/page color textures should be directly applicable to vertex textures as well.

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Yes, right. Generally it's the same. I don't know much about mega texturing, I didn't know that this technique is applicable for heightmap based terrain geometry.
If I use texture paging/terrain paging I think the size of the heightmap texture is important. I need more details please.

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I haven't done anything significant in this direction either but i don't think that there is one best size to use for your textures here. Bigger textures need more time to load, smaller textures meens you have to reload more often.
Why not read up a little bit on the techniques lc_overlord mentioned and build a little demo app? Shouldn't take that long and would allow you to try out yourself what sizes work best and try some methods to determin what terrain tiles/patches to load when.

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I think what Sebbit says is valid. You want to look into Clipmap Texturing, MegaTexturing (not a lot of technical information has been published afaik), virtual texture (e.g. sparse virtual textures). Maybe you can use this (http://www.gamedev.net/community/forums/topic.asp?topic_id=504549)?

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Quote:
Original post by Hiyar
This approach saves memory, but like I said terrain size is limited by the maximum texture size.


Terrain size is never limited by max texture size, it only limits it's resolution.
Far away you really want less resolution, it's only up close you need more, and mega texturing does this.
As far as i understand this might save memory under the right circumstances, at least make the memory it takes up constant, and if it takes up to much you could always drop a layer in resolution.

Quote:
Original post by Hiyar
If I use texture paging/terrain paging I think the size of the heightmap texture is important. I need more details please.

Oonly for the individual pieces, there are two main issues to it.
1. your dealing with individual textures here meaning that your doing a lot of texture binding and that they have to match up with the individual mesh pieces you render.
2. it really doesn't take LOD in consideration

Geanerally speaking the streaming part of these two methods are almost the same, it's what you do with it later that differs.

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My terrain is tiled/chunked. If the file for the tile doesnt exist, it generates one from an array of heightmaps (one tile would be only a part of a height map). This is for initial generation of terrain, usually the terrain is already packaged as a file. I use several LOD's, which are just different index buffers at the moment. The terrain objects are a linked list in 2 dimensions, and they add and release as you move around. The data is stored as byte[] because .Net streaming is too slow. I go straight to/from the graphics card, so I dont have to worry about marshalling. I dont know if this is the best way of doing it, but I am happy with performance so far.

I should say, terrain, not including water, trees etc renders pretty fast regardless in my experience. Its all the other add ons that really test your engine.

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Quote:
Original post by lc_overlord
Terrain size is never limited by max texture size, it only limits it's resolution.

If using vertex texture without any kind of streaming, max texture resolution supported by the hardware limits the terrain size. That's what I mean in the above post. (Generally, using vertex texture reduces memory cost, because I can use a single small vertex buffer for the entire terrain, rendering (and LOD) is done by using scale and bias in the shader)

I will look into geo clipmapping, but initially I wanted to know how to use multiple heightmap textures.Take a look at this paper:Click (Read terrain part)

They are using multiple vertex textures and a single vertex buffer for terrain rendering.(if I understand that correctly). I wanted to how is the streaming performed, if using several vertex textures.

Edit: Typo

[Edited by - Hiyar on January 17, 2009 12:43:21 AM]

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