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SetMaterial & SetTexture

Started by hksduhksdu Jan 6, 2005 at 9:03 PM 3 replies 800+ views

Original Post

Jan 6, 2005 at 9:03 PM

Hi, I would like to know if this will slow down the rendering loop or not. Assuming I have a sorted list of materials; 10 red, 5 yellow, and 16 blue. If they are not sorted, there will be a big performance problem because of too many SetMaterial switches. My question is, after sorted, there are only three switches. However, for 10 red, I am still doing: // For red for(int i=0;i<10;i++){ g->SetMaterial(Red); g->....draw the mesh here; } In this case, does that 9 extra SetMaterial actually count as switches so it will degrade the performance like unsorted list? Thank you very much, Andy

Promit

Jan 6, 2005 at 9:06 PM

If it's not a pure device, it might have redundant state change checks, but I wouldn't rely on it. What you really ought to do is code some sort of render queue system that does the sort, then binds each material/texture and renders everything that's using it.

hksduhksdu

Jan 6, 2005 at 9:09 PM

Thank you for replying. My SceneManager is using SceneGraph as the data structure. So when SceneManager is rendering the meshes under a group, every leaf(mesh) has their own SetMaterial and SetTexture even though some of them are using the same ones. So if I am not using RenderQueue, how do I counter this?

Thanks in advance,

Andy

Promit

Jan 6, 2005 at 10:26 PM

The cheap, slightly hackish way is to simply keep track of what texture and material you're using, and do the check yourself.

Althouhg I would encourage you to try a queueing mechanism...it's like a breath of fresh air.

circlesoft

Jan 6, 2005 at 10:37 PM

One of the important functions of a good SceneGraph is to group the entities together, based upon their material properties. I group objects in the following order:

- Shader
- Textures
- Non-Matrix Constants
- Matrix Constants

This way, I can batch objects quickly and efficiently. You do not want to put all the objects into one queue, then have an algorithm that linerarlly sorts them - this takes up too much time (especially if you have lots of objects and critera to sort upon). If you code a good scene graph that can categorize nodes efficiently, you will be much better off.

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