Can a triangle be flipped?
Blitz3D Forums/Blitz3D Programming/Can a triangle be flipped?
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| 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. |
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| 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. |
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| 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! |
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| 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 :) |
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| 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. |
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| 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. |
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| OK, can you or anyone post an idea of the most effective way re-builinding tris could be done? Code would be appreciated. |
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| I believe you can just swap verts 2 and 3 to flip a tri. |
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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. |
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| 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)! |
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| 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. |
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| What effect are you trying to achieve here...maybe some extra lateral thinking is needed? |
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| 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! >:) |
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| 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. |
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| 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. |
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