closed meshes necessary?

rollin

Hi, I need again the Help of our tech crew here on board


How important is it to build closed meshes for performance?

Like the question: "Delete never seen backfaces or keep the mesh (object) without holes"

I've heard it's not that important anymore but let's face it for different systems



iphone/ipodtouch/ipad

nintendo ds

psp

pc - high end

pc - low end (web based)


if anyone has knowledge about any of these (or other) systems I'm also interested in the "why" (if it's not going too deep into the matter :poly122: )!

iniside

It depends on engine. From What I have seen for CryEngine2 is essential to close for mesh, for Unreal not that important, but it's worth to close mesh anyway.

Why ? Because it can extremely increase DrawCall amount, which kill your performance very quick.

CrazyButcher

inside,why would holes increase drawcall counts? the rasterizer has no clue about how stuff is connected. not breaking up stuff has the benefit of vertex-cache reuse, but removing stuff is not gonna hurt performance.

tight meshes are ideal if you do oldschool stencil shadows.
For newer effects it's also practical to have closed meshes, so that things like screenspace "depth" of an object can be estimated. It also allows to use the first distance layer for more accurate SSAO.

anyway yes it's totally engine dependent.

iniside

CrazyButcher wrote: »

inside,why would holes increase drawcall counts? the rasterizer has no fucking clue about how stuff is connected

Don't ask me. I just done some tests with open and closed meshes. And in CryEngine2 it's gone crazy ;e.

CrazyButcher

interesting, but seems very engine specific then. hardware just plows through triangles, not caring so some effect by them must rely on this or so.

rollin

iniside: so what if you want to build a level with modular environment objects? do you need to merge everything together?!

Farfarer

After some dicking around on homebrew DS a few years back, it seems that it has the same issues as old-school 3D engines, i.e. the z-buffer isn't very accurate. So a closed mesh will mean less odd clipping as small decimals get rounded up/down in opposite directions.

The other platforms I think it's more of an engine limitation rather than hardware.

Buzzy

Clipping is very expensive on the lower-end platforms and z-buffers aren't terribly precise. So try to avoid intersecting meshes when possible. I wouldn't go out of my way to do it, but it should be a consideration.