Or more generally, a box shape between two perpendicular walls. Here's a screenshot from Blender of the shape I want: It's basically for a wall around a keep that joins onto another higher tower. I've done it by extruding up from the main part of the wall, but of course that leaves a face coplanar with the tower. My question is: how would you go about modelling this, quickly and efficiently (polygon-wise), avoiding the internal face?

Delete the unwanted faces?
you have to rearrange the edges on that tower wall too, skinny triangles like the one seen there are evil.

Edit: To elaborate further, split the face from the tower such that instead of a quad you have 4, align their edges with the smaller wall and delete the now hidden faces from both the tower wall and the smaller "fence", merge the vertices from the wall and the fence that occupy the same position.

I wouldn't want to just delete the faces, I want to keep it manifold in case I want to e.g. use it as a physics mesh in future (quite likely), and because I don't like the idea of dangling one-sided polygons :) Maybe I'm just being too programmer-y about it though. I'll tidy up the skinny polygons later, I know they can cause problems with physics and so on, and I think I can do that fairly efficiently.

Thanks for the tips, I think I could fix it up now, but how would you go about creating this arrangement from scratch? So you have the tower and the flat bit the little 'fence' is on, but no fence, and no skinny polygons (they were created because I split edges on the flat bit to have something to extrude from). There has to be a more efficient way than doing it the dumb way and fixing it up vertex by vertex. If doing simple things like this are that complex, you artists have just earned a whole lot of respect from me given the stuff you produce ;)

One sided polygons? I am not sure I get what you meant there.

Anyway if you were to do your level as a single mesh, I think it would be better to do it the way I said... unless I wasn't too clear or I am missing something.

That said, you could use Constructive Solid Geometry constructing each piece out of a box, removing the hidden/inaccessible faces either on a "level compilation" phase or during run time (for example by assigning them a specialy named texture image), that is how Quake and Unreal games do it (although one is additive and the other subtractive), that's how I do it, it is very collision friendly because all of your level geometry fragments (called brushes) are convex.

Sorry, the 'one-sided' doesn't make any sense, I should have left it as 'manifold', i.e. no holes, topographically. Just deleting a face will leave a hole in the mesh, which doesn't play well with physics, even if the hole wouldn't be able to be seen as it's flat against another face.

Also I should have been clearer, this is just a single game object, not part of a level. I don't think CSG would be appropriate really :) And in any case, I know there are plenty of ways to achieve the shape I want, I'm just looking to expand my modelling knowledge with a quick way to do it using standard 3D modelling tools, rather than moving vertices around and creating faces manually.

So the question is really: if you had a model without that little fence, and wanted to put the little fence there but avoiding holes and internal faces, using standard polygon modelling techniques, how would you do it?

I'd model it with quads on the tower face and rampart floor, and then extrude from either side, delete the overlapping faces, and weld matching verts.

That's what I was looking for :D (EDIT: sorry, that sounded like I'm discounting your advice Kwizatz! You've been helpful too and I've rated you up)

How would you make sure the quads lined up? Say you extruded from the rampart upwards, how would you make sure you extruded exactly as far upwards as the quads you'd made in the tower face? If you get it wrong you'll either make the little fence bit wonky or end up with wonky edges on the tower face. I suppose it's easy enough to enter vertex coordinates manually though.

Quote: Original post by BCullis
I'd model it with quads on the tower face and rampart floor, and then extrude from either side, delete the overlapping faces, and weld matching verts.

Thats exactly what I meant, thats what I get for not using pictures [smile]

Hah, sorry, I must have misunderstood :) I edited my post while you were writing yours though, hope you like it :)

Quote: Original post by hymerman
That's what I was looking for :D (EDIT: sorry, that sounded like I'm discounting your advice Kwizatz! You've been helpful too and I've rated you up)

How would you make sure the quads lined up? Say you extruded from the rampart upwards, how would you make sure you extruded exactly as far upwards as the quads you'd made in the tower face? If you get it wrong you'll either make the little fence bit wonky or end up with wonky edges on the tower face. I suppose it's easy enough to enter vertex coordinates manually though.

In Blender when you merge vertices (select first vert, select second vert, etc then press 'Alt-m') it asks you if you want to merge at the first vert, last vert or an average, make sure you merge to the vert that is on the tower and is coplanar with all the other quads.

[Edited by - Kwizatz on November 19, 2009 9:22:27 AM]