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In 3d terrain that consists of thousands of cubes (i.e. Minecraft ), what is a way to handle each block in terms of location and rendering? More specifically, I know that drawing a primitive of a cube and world transforming it everywhere in directX 9 is probably a ridiculous way to accomplish this since there are so many performance issues, so I was wondering what a more reasonable method would be.

Should each cube be a mesh that's copied many times, or is their a way to create the appropriate meshes from the data in your vertex buffer?

I found this article that walks through some of the theory behind implementing what I want to implement, but I've never used octrees before so I wasn't able to take too much from the source code. If octrees are indeed the way to go, where is a good starting point to learn about them? Most of my google searches only turned up blog posts about theory with little or no implementation examples.

It seems like using voxels would be useful in doing this, but like with octrees, I'm coming from no experience here, so I don't really know what to study first.

Anyway, thanks for any advice\resources\book names you can spare. I'm sure it's obvious, but I'm still very new to 3d programming, so I appreciate your help.

Kiran
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Aztal
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3 Answers3

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First off if you're using Minecraft as your reference, think of their use of chunks and relate it to Oct-trees. Minecraft divides up their world into smaller chunks to handle the massive amount information that is needed to be stored so use Oct-trees to organize this data that will be stored. Goz has a very accurate description of how Oct-trees and Quad-trees work, so use his information as a reference.

Another thing to consider is that you don't actually want to draw every cube to the screen as this will eat up your framerate. Use Object Culling to only draw visible cubes to the screen. Again if you think Minecraft; have you ever encountered a glitch where you can see through the blocks and under the world? This is because Minecraft only draws the top layer of blocks. With this many objects on screen, it would be a worthwhile investment to look into Object Culling using both the camera frustum and occlusion query.

For information on using DirectX I would recommend any book by Frank Luna. I own this book myself and it never leaves my side when programming in DirectX. http://www.amazon.com/Introduction-Game-Programming-Direct-9-0c/dp/1598220160/ref=sr_1_3?ie=UTF8&qid=1332478780&sr=8-3 I highly recommend this book as I've learned almost everything I know about DirectX from it.

Upon a Google search I found this link that discusses Occlusion Culling, because Luna doesn't cover occlusion culling, only frustum culling. I hear the Programming Gems series mentioned a lot, but I can't attest to its name personally. http://http.developer.nvidia.com/GPUGems/gpugems_ch29.html

Hope this helps.

SeventhBullet
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  • Thank you so much! I've heard great things about the Frank Luna book, so I think I'll take the time to go through all of it. By the way, once you have culling implemented and you know which cubes you want to draw, are you still drawing them one at a time with individual draw calls, or is there a better way to do it? Thanks again. – Aztal Mar 23 '12 at 11:48
  • Objects can only be drawn one at a time. If you have multiple objects rendering to the screen, build a class to handle their information and a vector to hold each object. Pass this vector into your render loop and iterate through each element in a for loop calling their render function. There are more ways to streamline this further, but I'll leave that to you to mess with. There's never any harm in playing with it and tweaking the code until it's just right. – SeventhBullet Mar 24 '12 at 02:26
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Oct-trees are fairly simple, especially axis aligned ones like those in mine craft.

It is basically just a 3D extension of the quad-tree. You may find it easier to learn about Quad-trees first.

To give you a quick overview of a quad-tree; basically you start off with a square. Now imagine placing a much smaller square in that square. If you wish to build a quad tree representing it you first divide the original square into 4 equal sized squares.

Next you check each quadrant and if the smaller square is in that quadrant you split that quadrant into 4 smaller sized squares. Then you check those 4 quadrants choose the quadrant and subdivide. Eventually your smaller square will be wholly contained in one or more quadrants inside quadrants inside quadrants (etc). You have now built your quad tree.

Now if you imagine you are searching for a specific square inside the larger square you can quickly see the bonus of a quad-tree. Instead of searching every possible square in the quad tree (equivalent to searching every pixel in a texture) you can now check the first 4 quadrants to see if they contain it. If one does you can check its 4 sub quadrants and so on until you find the smallest quadrant wholly containing your square (or pixel). This way you end up doing many fewer tests to find your object.

Now an oct-tree is basically the same thing but instead of encoding squares in squares you now encode cubes in cubes. Every cube can be split into 8 smaller octants (and hence the name oct-tree).

Oct-trees have the advantage that by knowing which octant you are starting in you can easily cast rays through the oct-tree to find collisions (as an octant is either full, partially full or it is empty). If an octant is empty then you pass right through it and then check the octant on the other side. If it is partially full you check its sub-octants and so on until you either find a full octant (ie you've hit a solid cube and you render it) or you pass through the octant entirely and hence there is no cube to render. This is how minecraft works (I'm guessing anyway ;)). This is also a good way of quickly rendering voxel data which more people are looking into these days as a possible future rendering mechanism.

Hope thats some help! :)

Goz
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  • Thank you very much, that helped a lot! Very clear explanation. I'll look into Quad-trees first and go from there. – Aztal Mar 23 '12 at 11:50
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Oct-trees and quad-trees are useful for culling sections of your geometry to render. Minecraft uses 16x16x16 render blocks to break up the terrain into manageable pieces.

Another technique to consider is instancing. Instancing is where you tell the GPU to render an object multiple times in different locations. It's used for crowd rendering, trees, anything where the geometry is the same, but you have lots of them.

http://msdn.microsoft.com/en-us/library/windows/desktop/bb173349(v=vs.85).aspx

http://http.developer.nvidia.com/GPUGems2/gpugems2_chapter03.html

Here is an article where the writer duplicates the minecraft renderer in OpenGL 4. While the code won't apply to your case the techniques (culling cubes that are surrounded, etc) can be applied to a directx renderer.

http://codeflow.org/entries/2010/dec/09/minecraft-like-rendering-experiments-in-opengl-4/

Don't be fooled by the blocky graphics and the low quality textures. Minecraft is an extremely complex renderer and you'll need to come up with ways to handle the sheer number of items involved. For example even a "small" part of the world, say 100x100x100 blocks is 1 million blocks. To push each block to the GPU as a separate mesh would kill your GPU. The Minecraft renderer is far more complex than most first person shooters when you get down to the technology.

Cameron MacFarland
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