Best way to sort draw calls?

Chapa · 2014-08-07T08:06:12

Hello, before anything, sorry for my english, since it is not my native language i am not really good on it, but here i go... Im new to DirectX and i been thinking on the best way to manage the draw calls i will be doing, so i can get the best performance i can, i now understand a good way is sorting the meshes on a way that i make the less state changes possible, for example sorting by shader, then materials, etc, and i been trying to approach this, but also thinking in the future when i will be needing to get control of a certain mesh, or test collisions, etc, and i been trying to search for this info, but no one talks about models having more than one mesh, and managing all those meshes together, etc... So this are the 2 ways i think i could do it, but cant decide which one is best or which one to choose... Lets say i have a material, mesh and model class and each mesh has a link to the material it uses... So the first idea would be loading all the materials and meshes on a list, and on the model class only saving a list of pointers to them, so i can modify or check something if needed, for example changing the world matrix of all the meshes on the model, the benefit of this idea is that i will be able to sort all of the meshes in the scene, ignoring to what model it belongs, and render them by material, saving material state changes even if two or more different models uses the same material, but the bad part is that i will be updating the matrix buffer on each mesh, to be able to move different meshes to the same place, ignoring their place on the list. My second idea would be loading the materials and meshes inside the model class and by that way only having one world matrix for the whole model, in this case i will be rendering by model, and inside it, rendering by material anyway, and the benefit would be only updating the matrix buffer once per model, instead of once per mesh, but the bad part here is that if i have the same material on different meshes between models, i will need to update the material again on the other model or models. So this are my 2 ideas and i still cant decide which one to choose, i really would appreciate any advice thank you.

Graphics and GPU Programming Programming

Started by Chapa August 05, 2014 07:44 AM

10 comments, last by Chapa 9 years, 8 months ago

TheChubu

9,484

August 07, 2014 08:04 AM

Only the mesh needs a vertex buffer. Sub-meshes can do with an index buffer and an offset into the shared vertex buffer.

If you "collapsed" all the sub meshes into a single vertex buffer, why don't go all the way and "collapse" all sub mesh index buffers into a single one? Unless I'm missing something you'd only need to append each index buffer into a single one and it would work.

Then again, you'd need to store an offset (and size) into the index buffer then, so when setting parameters per submesh you can draw only the submesh rather than the whole buffer.

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Chapa

136

Author

August 07, 2014 08:06 AM

Thank you L. Spiro, with this information it is really clear for me now how to save the data, you have been very helpfull, and i really appreciate the time you are taking to answer me, but i still cant get the whole idea, i understood how to structure the info and also i understood how i could manage the physics and even i got the LOD idea, its pretty simple when using this structure...

But i still cant get, how am i going to put this kind of structure into a render queue, the only idea i get for rendering this, is just having a render method in the model, which is going thru all meshes, and then each mesh is going thru all submeshes, and of course activating what needed on each stage, and finally getting the render of a single model,... the benefits i see on this way is that i will only update constant buffer on each mesh, if its different of course, and i can share the vertexbuffer, even the indexbuffer, just using an offset on the drawcall and knowing the size, but i still will change the material and probably texture for each submesh, which is what everyone tries to avoid, thats what i have been reading everywhere, of course after sorting by rendertype and shaders, this still confuses me...

And again, i am sorry for my english, may be you already tried to explain me this before or gave me an idea about it, but sometimes when reading a whole sentence its just hard for me to understand everything you are trying to tell me.

Thanks again

Best way to sort draw calls?

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