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Draw many independent objects


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#1 ynm   Members   -  Reputation: 170

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Posted 21 July 2014 - 07:12 PM

Hi everyone,

 

I tried simulating tank track, and it seems the hardest work is drawing many objects (meshes) on screen. The physics is not the problem, e.g just cast several rays. There is other solutions to draw track, but I like drawing detailed track, and making it the main selling point (feature).

 

For example, each tank like US Abrams has about 80 pads, and exactly the same links between track. So each track has about 160 independent objects, and each tank has about 320 objects (detailed meshes), not considering other parts of the tank. For a game with about 16 players, I need 16 x 320 = 5120 objects

 

I used Unity engine, which is limited in many ways. So if I use another engine or write one my own, what is the best method to draw many independent objects like above mentioned? If I need to choose engine, which feature do I need?

 

I imagine something like using GPGPU could solve that, but for old computer, it is not available, and I am don't know for sure will it work or not.

 

Any advice?

 

Regards



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#2 frob   Moderators   -  Reputation: 20298

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Posted 21 July 2014 - 07:52 PM

Draw calls and state changes are inherently expensive. Most games take big efforts to minimize draw calls.

You do not draw each link in a tread individually. For a tank tread, you would have animators come up with a small number of animation frames that move the treads (perhaps 6 or 8 or so frames) and use a single mesh. Your entire tank can be combined into a single object that is animated and drawn as single call, or if you cannot design around it, two calls. Not 160 draw calls.
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#3 Gian-Reto   Members   -  Reputation: 737

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Posted 22 July 2014 - 02:50 AM

If you keep using Unity, and have a budget to spend, check out "Mesh Baker" in the asset store. Helped me with a similar problem, reducing my vehicles 14 individual Meshes to a single skinned mesh. Also it has functionality to bake different UV Textures into a single atlas, which is also something you will have to do.

It is now drawn in a single draw call (or at least with 14x less draw calls), thanks to that I can use more vehicles in the same scene, while still being able to move the parts of the mesh as if they would be individual objects.

 

If you lack the funds for the Mesh Baker, I guess you can get the same effect in any 3D Package like Blender or 3DS Max. Of course, then you need to know yourself how to bake a texture atlas and combine the objects into a skinned mesh, but I guess there are plenty of tutorials on that on the web.

 

 

And I wouldn't hope any engine will solve that problem for you. As frob already hinted at, its more a problem with the underlying abstraction layers like DirectX or OpenGL. So you would need to code to the metal if you wanted to get around draw call limitations (that is why mantle is such a big thing for some people).

 

It is certainly easier to invest more time in preparing your 3D Objects than coding such low level functions yourself.IMO of course.






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