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Rendering vertices for my Terrain

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Hey All. Im trying to do a 2d terrain which will be viewable from plan view. So I started it and all was looking good. Ive got my vertices in position. And here is how my 2D terrain vertices are positioned(its only 4x4): - - - - - - - - - - - - - - - - - - - - - - - - - Now i know i could use a Triangle Strip 4 times to render my terrain but i was hoping for a better approuch, as i wouldnt call a bunch of DrawPrimitive functions for a 3d terrain. Any ideas.

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Actually, a triangle strip is a loss on hardware with a transformed vertex cache.

With a triangle strip, the best you can get is asymptotically close to one triangle per transformed vertex. With a triangle list (not strip), sorted for the vertex cache, you can get about 1.5 triangles per transformed vertex on a reular mesh like this.

Thus, the list will outperform the strip.

Note that you don't need one index list per terrain block, only one index list per terrain block size -- all, say, 32x32 terrain blocks will use the same index list (unless you do LOD through border decimation, in which case you'll need 15 lists total, for the different LOD combinations).

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I read the first link and not sure whether i understand it. Please correct me if im wrong.

Say these are my vertices for the terrain terrain:

01 02 03 04 05
06 07 08 09 10
11 12 13 14 15
16 17 18 19 20
21 22 23 24 25

In my vertex buffer would i do the following:

06,01,07,02,08,03,09,04,10,05,11,06,11,06,12,07,13,08,14,09,15,10,16,
11,16,11,17,12,18,13,19,14,20,15,21,16,21,16,22,17,23,18,24,19,25,20

then a call to DrawPrimitive as follows:

DrawPrimitive(D3DPT_TRIANGLESTRIP,0,however many pollygons);

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The post is actually more correct than the article.

The order, as modified by the post, would be:

06,01,07,02,08,03,09,04,10,05, 05,11, 11,06,12,07 ... and so on

I confirmed this by writting a quick program using that order using an index buffer.

[Edited by - skillfreak on January 21, 2006 10:43:31 PM]

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Someone came up with a trick called "Priming the vertex cache" which can help get larger terrain tiles while keeping more data cached.

Now lets say we're doing a 16x16 tile. The vertices (hex numbering) are like so:

00 01 02 03 04 05 06 07 08 09 0A 0B 0C 0D 0E 0F
10 11 12 13 14 15 16 17 18 19 1A 1B 1C 1D 1E 1F
20 21 22 23 24 25 26 27 28 29 2A 2B 2C 2D 2E 2F
...
F0 F1 F2 F3 F4 F5 F6 F7 F8 F9 FA FB FC FD FE FF

Typically the indices would be (in list form)
00,01,10, 10,01,11, 01,02,11, 11,02,12, 02,03,12, 12,03,13, etc...

Note that by the time we start the second row of triangles, we've looked at 32 vertices (16 on top and 16 on bottom), and the 10,11,12,etc, vertices which we need to begin the next row are long since out of the cache.

Instead, we begin with a bunch of degenerates
00,01,01, 02,03,03, 04,05,05, 06,07,07,...,0E,0F,0F

Now row 0 is in the cache, in order, with nothing drawn. Now draw row after row as normal, and the vertices removed from the cache FIFO will always be ones you'll never be needing again.

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