Cutting 3D meshes

[andylegate]

Ooooookay....

So I've got this wall, I've got it just the way I want it. Textured too.

Ooops, I forgot to put in a doorway, or a window, or it's later and I'm adding to the darn building.....

In anycase...how do I cut a hole in the mesh?

There's a great tutorial on Alcugs, but it has you staring with a plane, not a 3D object, and then making it 3D.

I've already got the mesh the way I want it, but now I need to cut it.

How? I've tried several things, but no go, the mesh goes back to how it was before, solid with no hole.

EDIT: Later, after a hot dog, and putting on eye glasses.... Oh......hehehe. So there IS a tutorial for that......*whistles some* Okey Dokey......here's the URL for anyone else that is blind as me...

http://alcugs.almlys.org/wiki/index.php/Dustin%27s_Fifth_Tutorial

[Chacal]

Anyone knows how Plasma reacts to that?
I remember in the old days of the Quake engine (or was it DOOM?), cutting a hole in a mesh was a big no-no as the engine would break it down in a lot of small polys and this would have a huge impact in performance.

[Paradox]

The cool thing about Blender, is that Plasma uses the same vertices and faces as Blender.

The hard part about cutting through objects is how Blender handles its Booleans. Booleans can be used to union, difference, and intersect two meshes. This usually creates a lot of unnecessary new vertices which can slow Plasma down.

[Chacal]

I suppose the trick is to go back and delete the unneeded vertices by hand.

[andylegate]

Yes, that' is what I did when I was done.

What I like about Blender compared to the Radiant that COD uses, is that you can intersect your brushes with no problems. In the Radiants, that was a big no-no. You had to bevel your edges to meet them together. If you did intersect your brushes, you would get a ton of BSP errors when you went to compile your map, and enough of those, and the map would not compile at all. Even if you got it to compile, you would end up with the "Hall of mirrors" effect where they intersected.

Just about any CSG operation (IE hollowing out a cube to make a room, etc) was a big no-no.

Then, in the Ravenshield editor, CSG's were how you made rooms! Complete opposite of the COD editors!

[Grogyan]

I put a question, exactly the same as this some time ago.

With Paradox's help, found that you need to,
1) Make a mesh with which to "cut" the original with.
2) Select that mesh in object mode and move it to where the original is to be "cut"
3) Hold down the shift key and select the original mesh
4) You should now have 2 meshes selected
5) Press the "W" key and select difference
6) Move or delete the 2 highlighted meshes and presto you will find a new mesh, cut in the way that you asked Blender.

Here is a video of the operation on YouTube.

http://www.youtube.com/watch?v=OlRgWgDrGxQ

[andylegate]

Thanks Grogyan.

There is one thing that both you and the Tutorial needs to mention though:

It's important to select the mesh that you are USING to cut with first, and the mesh that you want to BE CUT second.
If you do it the other way around, your cutter mesh is the one that get's cut!

This did work great, and I was able to make 6 windows in a flash.

[Grogyan]

Thanks Grogyan.

There is one thing that both you and the Tutorial needs to mention though:

It's important to select the mesh that you are USING to cut with first, and the mesh that you want to BE CUT second.
If you do it the other way around, your cutter mesh is the one that get's cut!

This did work great, and I was able to make 6 windows in a flash.

If you do it in the steps I have outlined, it should be ok.

I asked this same question before, cause I had done some CSG for Unreal Editor, and it was very easy to work with, all you have to remember is with Blender, when you use a boolean, use the new mesh and rename it, and delete the old.

[Aloys]

As Paradox mentions, the big problem with booleans operations in Blender is that 99% of the time they tend to create an awfull resulting mesh and you need to spend time cleaning the mesh manualy.. And when you do that on complex meshes the time you need to spend to clean the mess is prohibitive...
Blender 2.44 (and I guess 2.45 as well) as slightly improved that, but it is still far from great...
Personally, as much as possible I try to avoid boolean operations, I do most of my work manually in Edit mode; much like in the tutorial Andy mention in his first post..
If Blender supported proper CSG things would be much easier..

[Chacal]

Nice to know some things never change...

Three tricks I used back then:
- first split the mesh so that the mesh to be cut is as small as possible;
- manually delete unneeded vertices after the cut;
- do the cut, but only use the result as a template to build a new object manually, don't keep it.