Fig 1. Filling Menu

Fig 1 shows you what you get once you have hit the <F> key; a count of the number of visible holes, followed by a menu of further key commands down the bottom of the screen.

[edit] Automatic Hole Filling

<F> - Fill All 

Type <F><F> to fill all visible holes. You will be prompted for the number of holes to leave, so type something in and hit <Enter>, and all but that number of the largest holes will be filled. Just hit <Enter> if you really do want all visible holes filled.

<H> - Holes Only 

The Fill All tool doesn't distinguish between genuine holes and floating faces, its just looks for blue edges and fills between them. If you use this Holes Only tool instead, it will look more closely at the surrounding faces, and will only fill if its an obvious hole. The unfilled edges are protected (as if you'd used the <P> key).

<P> - Protecting Holes 

You can protect holes from being filled with <F><P>. <LMB> stretch a box over some holes and they'll turn from blue to red, indicating their protected status. Do the same again to unprotect those holes.

<U> - Unprotect All Holes 

You can unprotect all holes, making them fillable, with <F><U>.

[edit] Individual Hole Filling

The auto fill its a excellent way to fill a large number of small holes quickly, but for complex holes you may want more control over the fill shape. The <N> key can be used to fill individual holes.

<N> - Go To Next Hole 

Fig 2. Filling A Hole

Typing <N> will focus the view onto the next unfilled hole, and a new menu of key commands is displayed (see Fig 2).

If you are inside the <F> menu, the <N> key takes you to the next larger visible hole. If you use the <N> key outside of the <F> menu, then you are taken to the hole closest to the face under the mouse pointer. So, if you want to fill a specific hole, just aim the mouse pointer close by and type <N>.

<T> - Triangulate 

Fig 3. Triangulate Loop

Typing <T> will cycle through 3 different hole filling methods (see Fig 3):

1. The first method is to fill with approximately the same density of faces as the surrounding mesh; this may take a long time for very large holes, but you can stop it mid-way if you wish by holding the space bar, and you'll get fewer triangles.
2. The second method is to simply connect the boundary points; no additional points are added.
3. The third method is to insert a single point in the center of the hole, and then all boundary edges are connected to this center point.
4. Typing <T> a fourth time will take you back to an unfilled hole.

Occasionally a hole is too complex for triangulation, and an error is displayed. In those cases you can use one of the following tools to clean-up or simplify the hole ready for a second fill attempt.

<B> - Bridge 

Fig 4. Bridging

To connect together a pair of edges, use the <B> key. You might use this if you want specific edges connected with a perfectly straight line, or to simplify a complex hole by splitting it into smaller ones.

First move the mouse pointer over one of the blue highlighted edges, then type <B> and that edge will be highlighted with a thicker yellow line. If you have accidentally selected the wrong edge, aim the mouse pointer at the background, or some other part of the mesh (but not another edge!), and use the <Backspace> key to unselect it.

Next move the mouse pointer over the second edge and type <B> to connect the two edges. If you accidentally selected the wrong edge at this point, you will need to use the <Backspace> key to deleted all of the newly created bridging faces. In this case you do need to move the mouse pointer so its over the blue edges when holding the <Backspace> key.

If you are just viewing the mesh, you can also use the <B> key to bridge between a pair of blue highlighted edges (see Fig 4). Use <Backspace> again if you accidentally pick the wrong edges.

<Backspace> - Delete Edge 

The <Backspace> key can also be used to delete any blue highlighted edges. Just aim the mouse pointer at the edge and type <Backspace>, or hold the <Backspace> key down and move the mouse pointer about to delete multiple edges. Deleting edges with <Backspace> works both inside and outside of the <N> key menu.

<Space-Backspace> - Delete All Edges 

Delete all faces adjacent to the current hole with <Space-Backspace>. You might use this when the boundary of a hole is very messy and the triangulation fails.

<Home> - View Focus 

If you want to know where the current hole is in relation to the rest of the mesh, type <Home>. This shows you the mesh in wireframe, with an arrow pointing to the hole's location. Type <Home> again to get back to the zoomed in view.

<Enter> - Stop Filling 

To exit from the <F> key or <N> key menu, type <Enter>.

[edit] After Filling

All holes are filled with green marked faces (see the G - Mark chapter for more details). This allows you to perform other actions that improve the quality of the filled faces, such as smoothing. In particular, the default <F4> macro does an excellent job at cleaning up newly filled holes.