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Multiple Pass Rendering

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Hi All, Multiple pass rendering is killing my framerate for displaying my terrain in my engine when running on my laptop. My device's MaxSimultaneousTextures is 3, and I have 4 textures and an alpha map (each channel representing the blend of the next texture). Right now I have one pass per texture (4 passes total) where it takes the texture and alpha map and combines them together and then this is output onto the device with alpha blending. Am I really stuck to doing multiple passes here, or can anyone think of a way around the blending limit? Games like WoW run fine on my laptop and seem to do blended terrains so I assume they have found some way to do this without using multiple passes. Any advice would be appreciated. I am using DirectX. Oh, and there is no pixel shader on this card. Thanks! Rael

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During the many hours I spent playing wow, I noticed that even if the number of ground textures in an area could be like 5 or more, they only use perhaps 2 or 3 at the same spot.

So, if you render the terrain in different chunks which only needs 2-3 textures each, you can switch the textures in between, reducing the number of passes. This may or may not affect how you design your terrain, but unless you mix textures alot, it should not be a problem.

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Quote:
Original post by Necator

During the many hours I spent playing wow, I noticed that even if the number of ground textures in an area could be like 5 or more, they only use perhaps 2 or 3 at the same spot.

So, if you render the terrain in different chunks which only needs 2-3 textures each, you can switch the textures in between, reducing the number of passes. This may or may not affect how you design your terrain, but unless you mix textures alot, it should not be a problem.
That's a good point, I could definitely improve my rendering sort order. What is usually the biggest overhead... changing the fixed function pipeline stages or changing the textures? Is changing the textures still a big overhead even if they all fit onto the graphics card memory?

Thanks

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Keep in mind that you don't have to always do the blending right at terrain render time. If you've got a big stack of textures with alpha, you can composite them together for whatever terrain tile size you're using, and then use that texture to actually render with.

Also, if you're doing 4 textures, and the card can't support that many, you can still do 2 at a time (or 3, or whatever) instead of doing them one by one. I would, however, recommend going with the texture compositing approach.

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