Can a triangle be flipped?

Hi, i'm interested if any of you guys know if theres ANY way at all to flip an existing triangle or poly which is already part of a mesh, which was preloaded (such as b3d or 3ds). The only way i can choose which way the normal is pointing now is by adding the triangle myself and making the vertexes go in the proper order, but thats too slow. I need some triangles of a mesh to flip and flip back in real time.

Too bad those vertex normals are only concerned about lighting...

Edit: Problem solved, whole system was changed in favour of a better solution.

You have to clear all the triangles (not the vertices) and rebuild them with the one(s) you want flipped using a reversed winding order.

If you want it realtime and its the same triangles each time, consider having two versions of the mesh.

No its a few different triangles each time, they move around. There is also many of them. I already thought about what i think you suggested. That is to get the coords of each vertex around a triangle that needs to be flipped, and make a new tri there in reverse order. But that is kinda like making mesh which i read is _slow_ so any other suggestions I will try, before i head to test this one out.

If i get this right, i believe i'll manage to make a pretty nice contribution to the community so come on!

Another question then:

How much would it slow things down to have a 100 000 poly object hidden all the time during execution of the game? Using HideEntity of course. Would it slow anything down at all?

Edit- OK I guess I'll test myself now that i get the time :)

I'll continue talking to myself.

In case anyone needs this info:
I calculated that a hidden entity (b3d mesh in this case) costs ~ABOUT~ 1 MB of RAM for every 24000 polys (triangles) that it has. So far thats the only cost of having hidden entities that i have calculated, so again if anyone can enlighten me and tell me if there are others I'll be grateful.

Edit: Another test when they were not hidden showed 14000 polys per MB. Used planes instead of spheres too, so i cant be sure but who cares.

Your only option is to rebuild the mesh, but you are lucky that you only have to re-build the tris and not the verts as well. Vert data is much slower to upload to the card.

OK, can you or anyone post an idea of the most effective way re-builinding tris could be done? Code would be appreciated.

I believe you can just swap verts 2 and 3 to flip a tri.

Something like,

      tx#=vertexX(vertex1)
      ty#=vertexY(vertex1)
      tz#=vertexZ(vertex1)
      PositionVertex Vert2,VerteX(vert3),vertexy(vert3),vertezZ(vert3)
      PositionVertex Vert3,tx,ty,tz

Also, you need to swap vertex color/normal/tex coord data. I'd still prefer it to rebuilding the mesh from scratch though, probably alot faster.

Mhm ok thanks for that advice guys.

But in the meanwhile i had a break and a cookie and also a revelation. So i'll use a different system altogether... Meaning this thread can go and sink. When i'm done with this i hope its good (ie fast)!

You can't just reposition vertices like that without messing up other dependent triangles. You could of course unweld all your triangles, but as I said before, any change you make to a single vertex will be slower than rebuilding all the triangles, because it will have to re-upload all the vertices anyway.

What effect are you trying to achieve here...maybe some extra lateral thinking is needed?

I'm trying to achieve something pretty interesting and useful for the community. Don't wanna brag about it till it actually works, so it'll be my little secret!! HAh hAH! >:)

Btw, if you just want to flip every tri in a mesh, FlipMesh Entity already does that. Or perhaps it just switches culling modes..but same siff.

lol
Uhh... yea, i kinda know that SpacedMan :D i think i pretty much read the whole command refference by now about 10 times, 2d and 3d A to Z so... i know... ;)

I also found a few commands missing in A-Z and appearing in Category listing, and vice versa.