# Terrain drawing question (list vs strip vs.. mesh..)

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Well, I'm startin my first 3d project thingamajig to learn this stuff.. and I'm drawing a terrain thing. If I get upwards of 25k triangles, things start getting too slow. I store an array of vertices and slope vectors so I can have stuff bouncin around the terrain fairly realistically etc. Right now I use a triangle strip, and draw the terrain one strip at a time with successive calls to DIP. I do this cuz I can't figure out how to put the whole darn terrain into one strip or fan.. Should I just use a huge list of triangles then?? That'd be a lot of indices, but hopefully for a performance gain. Another idea was to use a flat mesh, then fill in Y values, vertice normals for lighting, and my slope vectors, as they do in the d3d billboard example. Maybe meshes are optimized and can draw faster as well? Then there's this thing called "BSP" or even "scene graph" that I frankly don't want to get into at this time.. So any tips would be handy and helpful! Thanks!

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Yeah you should most definetly batch a bunch of triangle lists together and draw them in one go. And don't think scene management has to be difficult. It can be, but in this case it can be pretty easy. Just look into a thing called quadtrees, and that should be enough for your terrain rendering.

The basic idea is to divide a flat plane into 4 nodes, and divide each nodeinto 4 more pieces and etc... You end up with a hierchical list of small nodes (a tree of nodes, each node with 4 children). Check each node against the view frustum (which by the was is a very simple process) and add all the triangles in that node to a list, when you've traveresed the entire hierarchy, draw all the triangles in the list you created. This will not only give you a performace boost, but will aloow for much more larger terrains.

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Thanks for the reply! I think I was lumping such a quadtree into the BSP category in my mind.. but I think I could handle that :P You'll have to tell me how to batch the triangle lists though.. Thanks again!

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Quote:
 Original post by n0obThanks for the reply! I think I was lumping such a quadtree into the BSP category in my mind.. but I think I could handle that :P You'll have to tell me how to batch the triangle lists though.. Thanks again!

Well, each node would have a list of indices that the node contains. As you traverse the tree - determining which nodes to draw and which to not, you concatenate all the lists of the drawable nodes. You end up with one big list of indices that index into the vertex buffer. Then you DrawIndexedPrimitive on all those suckers.

so roughly speaking, something like:

void build_list( list& ilist, node* n ){  if( n )  {    if( n->is_leaf() && is_in_view_frustum( n ) )    {      ilist.add( n->get_index_list() )    }    else    {      build_list( ilist, n->get_child_1() );      build_list( ilist, n->get_child_2() );      build_list( ilist, n->get_child_3() );      build_list( ilist, n->get_child_4() );    }  }}

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So, it will be a triangle list then?  Blart, I guess you said that already lol [/edit] And I create the index buffer each loop I guess... Is there a nifty D3DX function for testing if something is in the view frustum? It seems that there should be, but I can't find anything in the help :/ Thanks again!

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Hey woot I found an article on this very thing >_<
http://www.flipcode.com/articles/article_frustumculling.shtml

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