Is there a simple tool for fixing invalid geometry in edit mode?

Question

I find myself often in a situation where I build an object out of simpler forms, well always ;) However when putting these together I sometimes have invalid geometry I must fix.

I wonder whether there is a tool for fixing this in edit mode?

The "Boolean" modifier operates on objects. I however want to operate on a small part of a complex object.
The knife tool is a step in the right direction. With this there is the problem I must hit the intersections precisely myself, which is not possible.

An example:
Before – 5 sticks intersecting the long main stick

After – Geometry corrected. No more intersecting faces

Is there a way Blender can do this of its own (selecting multiple faces and Blender splits the edges and faces as needed)?

Answer 1

There is an addon called BoolTools that can help with this.

It's a two step process. First select the entire mesh and separate by loose parts, then union the component parts.

Answer 2

A suggestion is to consider other modeling techniques and tools. Then you will have less need to determine locations of overlapping faces and delete them. Deleting faces is very useful and quick. Determining the locations seems inefficient. Boolean operations are useful and more necessary for complex 3D shapes, yet your examples are very rectilinear.

In the object sequence above, faces are only created.

• Stage01 Simple Scaled Cube [Edit Mode]
• Stage02 Loop Cut then Bevel
• Stage03 Duplicate all vertices, Translate X, Select Middle near faces, Bridge edge loops to create horizontal bar connecting vertical stacks.
• Stage04 Shear
• Stage05 Extrude of Stage02
• Stage06 Array Modifier on Stage05 to create longer sequences of mesh. Array Modifier panel is shown above.

If I happen to mention 4 or 5 tools, there are 30 I have not mentioned.
A few minutes watching videos showing general built in Blender tool capabilities might be an efficient use of time. I have not looked for add on tools for your specific situation.

Answer 3

Not for this kind of situation, no. Mostly because there's nothing technically invalid about coincident geometry. Invalid geometry is called "non-manifold," and there are tools for identifying it like "Select -> non-manifold." But even non-manifold geometry has its uses.

But the situation that you're looking at isn't necessarily invalid. In fact, for a game asset this might be a good way to limit polygon count (if you can resolve the coincident faces well).

The suggestions to study modeling practices are good suggestions because a non-trivial amount of good modeling practice is avoiding problems, as much as it is understanding how to solve them.

To avoid being unhelpful, though, there's not really a great answer to your particular situation. There's no tools that will detect where cuts need to be made so that you can connect those two meshes. No matter what solution you choose, it will necessarily involve some amount of guessing about where to cut the horizontal piece, and then manually attaching the vertical piece. Even separating them into different objects so that you can Bool them together is problematic because you'll still have to manually tweak the Bool result.

However it might not be a problem worth solving. The only problem with coincident faces is when they are exactly coincident. If they are mathematically in the same place, the renderer has to "guess" at which one is in front of the other. Computers are (at best) terrible guessers. They are, however, excellent precision...ers at precision. Which means the faces only have to be slightly separated in order for the renderer to know which one is in front of the other.

So, practically speaking, I'd recommend scaling your vertical pieces up (or down) by 0.0001. (You can do this in the numeric panel by manually entering the scale value in all three fields, or if you're comfortable with "ghost input" you can press s and then just type "0.0001" and hit enter). That'll be just enough for them to overlap the horizontal piece so that the renderer can differentiate them. But it'll be a small enough amount that the human eye won't really notice... it'll still look glitchy in the viewport, though.

Hope that helps!