Wireframes Cylinder

Ninjin

Hey guys,

I stumbled across something I have no idea of. When I look at the wireframe of a cylinder in Unreal Engine 4, then compare it to my imported cylinder from Blender, it looks totally different. Can someone explain me this and give me some technical inside + performance explanation, why is UE4 these loopcuts, just to texture better, but why on the top?

I'm assuming the UE4 has 4 loopcuts in the height and on the top 1 loopcut. The Blender mesh, has no loopcut and on top of the cylinder, I used an NGON, which I heard is really bad ^^.

Eric Chadwick

I'm not sure why Epic does this with their cylinder primitive.

I know this type of mesh works better when tesselated, because the triangles are more evenly distributed. Tesselation is used for displacement, here's an example:
http://wiki.polycount.com/wiki/NyraCharacter

The ngon in your example is not too bad. As you can see it has been converted into triangles when imported into Unreal Engine. This happens with most game engines.

The biggest problem with a ngon is you are usually not able to control the shapes of the triangles it will create. Here's an example, same vertex positions but different triangles are created:

http://wiki.polycount.com/wiki/Polygon_Count



Another problem with your ngon, it has created long thin triangles. This is generally bad since the game engine becomes inefficient when rendering the model.

ZacD

Also extra edge loops allow you to do more with vertex painting and vertex animation. Except for extereme cases, high polycounts in UE4 aren't going to have much of a negative impact on performance.

Ninjin

I also started reading "GPU Gems" (first edition though, 2003 ). There was some part about Lightning. In 2003 there seemed to be 2 different methods for lightning, per-vertex and per-fragment lightning and also with tesselation (which is just higher resolution?). If you have more vertices, you can produce better light and stuff
Still thanks alot for helping me out

ZacD

That book is very outdated, most games use pixel shading, Mobile games will sometimes use vertex shading.

Eric Chadwick

You mean lighting not lightning.


Vertex lighting is still used quite a bit on mobile for performance reasons. I bet we'll see it used a lot on first generation VR, at least until the hardware catches up.

Ninjin

"Pixel shaders, also known as fragment shaders" - wikipedia. If per-fragment lighting (thanks for teaching me some proper english ) is not the same as fragment shaders, holy, then I need to lock my door and get some brainzz

ZacD

Yeah, sounds like they are the same thing, you'll just hear the term pixel shader thrown around a lot more.