If you are using immediate mode to render your terrain, you will get a huge boost by switching to compiled vertex arrrays or VBOs. I haven't used OpenGL in a long time so I don't remember the details. It's not clear which is faster -- an indexed triangle strip vs. an indexed triangle list. So, try an indexed triangle list first because it easier to implement. Using textures is necessary for a good-looking terrain.

You should definitely switch to the VBO approach. Sending that many vertices down per frame is almost certainly your bottleneck.

Using vertex colors, as you're doing, is probably faster than texturing for the number of triangles that you have, but you might get better performance if you used a texture and created fewer triangles (say, one per 4 pixel block).


On modern graphics hardware (ATI at least), strip-ordered triangle lists are just as fast as using the actual strips, because the post transform cache is large enough. I would assume that you'd see a similar thing on Nvidia chips, but I'm not certain. What really matters is not the fact that you're using strips, but the fact that you're drawing triangles in an efficient order. Stripification can give you an efficient rendering order as long as your strips are long enough.

This is assuming you're using VBOs. If you use immediate mode then strips will be faster because you'd have fewer glXXXX() calls, but IMO you should switch to VBOs because they will be faster still.



JB

Quote:Original post by mrbig
I have three questions for now:

Fell for all the wrong ideas

Quote:
1. I heard that rendering using triangle strips could improve performance. How is it done?

This is by far the last thing you should try, because a) a triangle list sorted for cache efficiency will be just as good and b) it's not even likely that supplying vertices is the part of the pipeline that's slowing you down. It's like a factory. Whipping that fast guy to work even faster is useless, if that gonzo two places away takes all day to get his screws in.

Quote:
2. I've read the VBO tutorial on NeHe's site. At the end of the tutorial, the author also mentions rendering using triangle strips, but then says it's beyond the scope of the tutorial. So how do I render the terrain using triangle strips with VBOs?

Worry about how to use VBOs and absolutely forget about triangle strips for now. If you tried everything else and you are really SURE that vertex submission is the bottle neck, THEN you can worry about strips.

Quote:
3. In my renderer, every vertex corresponds to one pixel,

That's hard to imagine unless you are using parallel projection or your terrain is absolutely flat and you're looking straight down at it (and in that case, yes, it would be completely dumb to draw a gazillion vertices instead of a textured quad).
Apart from that, vertex colors will be fine, but unless you're aiming for a terrain renderer where you never actually get close to the terrain the simple reason to use texture maps would be the utter lack of detail with only vertex colors.

Without even knowing what you want to use the terrain for, it is pretty impossible to give useful advice, but generally you should cover all the basic "optimizations" before you even worry about strips or whether vertex colors might be .1% faster or slower than a texture. What about culling? And is there even any use for culling or do you plan to always have the whole terrain visible anyway? And in that case: how large do you plan to make it?

How are you drawing it now? The fact that you talk about glColor and glTexCoord calls somehow suggests you are the using the most basic, but also most awefully slow and inefficient hand feeding (ie. immediate mode) and should switch to vertex arrays in the very least (VBO would be better, but if it's too much for you, do vertex arrays first). If the terrain isn't supposed to change you could even try display lists (which are the opposite of flexible, but sometimes even faster than VBO).

Original post by Trienco

Quote:Original post by mrbig
3. In my renderer, every vertex corresponds to one pixel,

That's hard to imagine unless you are using parallel projection or your terrain is absolutely flat.../quote]

He is talking about how the terrain image is stored, not how the result looks on the screen.

@trienco: could you please elaborate why index triangle strips optimized for vertex cache efficiency should be the last option for pipeline optimization?

I held a seminar about vertex cache efficient triangle strips last winter and I can t agree with statements that claim that index triangle lists sorted for vertex cache efficiency can perform nearly as fast as optimized tri strips.

There s been an article at toms hardware sometime ago, but his judgement was kind of subjective without scientific value.

The only reason I see that one should start with index tri lists is because almost all index tri strip generators require exactly this storage format for strip generation.