More about Faces


#1

I’ve recently discovered the different faces, front and back. I’ve always noted the different colors of the 2 sides but don’t really know the difference, and still don’t.

I’ve noticed that, sometimes push/pull operates differently and sometimes it doesn’t, e.g. I was helping a neighbor who was making a drawer, when he pushed on the face on the back of the drawer it opened a cavity instead of making a board, I suggested pushing the other side (opposite face) and whala a board. I tried duplicating that here but always got a “solid” no cavity.

Is there an easy explanation of this phenom?


#2

It would be easier to diagnose what your neighbor was getting if we had his model but it sounds as if what he was doing was effecting the same as pushing an opening for a window (or a mortise) and this happens when the surface being pushed is bordered by at least one other face. You can see that here.

But if you pull the face in the opposite direction, it looks like it is a solid.


However orbiting around to the other side would show it is missing a face just as the first shot is.

This is perfectly logical behavior. If it didn’t work that way, you wouldn’t be able to cut openings as for windows or mortises.

As for the front and back faces, since SketchUp is a surface modeler, faces need to have fronts and backs. Think of it as building with AC grade plywoo. Keep the C grade faces on the inside of the project and the A-grade or front faces out. There are a number of different reasons to maintain proper face orientation. Since Push/Pull extrudes along a vector and vectors by definition have direction (positive or negative), the face orientation comes into play there. Other reasons for considering face orientation include the use of rendering applications. Many of them won’t render back faces even if they have materials applied to them.

An efficient workflow includes correcting face orientation when back faces show in 3D shapes. Keep up on it as you go and reduce the amount of work you’ll need to do later.


#3

Also, front faces are white and back faces are dark gray.


#4

You can edit the colors of the front and back sides of the default material. Because depending on shading it can sometimes be hard to tell the default gray from a poorly lit white, many of us set a deliberately garish color for the back so that there is no doubt.


#5

In addition to the above, note that you can tap [ctrl] and it will leave the face you are pushing/pulling so that the underlying shape your pulling from does not change.
(…Actually it might flip this face’s inside to out - if it’s an outside face, make sure that it still is an outside face once you’ve pulled it.)


#6

I use green instead of blue because it is easier for me to detect. A laptop on which I use sometimes SketchUp displays shaded front faces very close to the same color as the default blue-gray back face color. With the green I use, there’s no question.


#7

Thanks DaveR, I’m sure that’s what we were doing. Just 1 more reason to use components/groups.


#8

gadget2020, I’m not clear what the ctrl does, could you show an example?


#9

Ctrl (option on Mac) tells SketchUp to retain the original face. This matters when the face you pushpull borders on other coplanar face(s) because SketchUp by default assumes you want to push an indent into that surface. In this animation, watch for the little “+” to show up next to the cursor when I push the ctrl/option key.


#10

that’s cool, thanks!


#11

Yes, that’s SketchUp :wink:


#12

The “select only” tool will let you filter faces so you can flip them. Not a default tool, it’s in extension warehouse.


#13

Do you have a link to this “slect only” tool or the plugin that it is part of?

Tip:
If you have “Reverse Faces” assigned to a shortcut key you can easily flip faces while hovering over them with the “Push/Pull” tool while not having any face preselected.


#14

Sounds like Thomthoms selection toys…


#15

https://extensions.sketchup.com/en/system/files/tt_selection_toys-2.3.9.rbz)

You will also need to download https://extensions.sketchup.com/en/content/tt_lib%C2%B2