Can I model with in a mode where quads are all planar?

Question

I have started modelling with triangles and quads.

As many novice blender user before me, it took me a while to understand that my quads were in most case not planar.

For my project, I need my quads to be planar. I understand that I can use the Mesh->Clean_up->Make_Planar_Faces to flatten quads.

However, I find this a bit messy as soon as you have a lot of quads.

I would like to know if it is possible, when you make a face or move a vertice, to impose a "quad needs to be planar" constraint.

I mean, that if I select 3 vertices, Blender should be theorically able to put the 4th vertice in the same plane as the 3 others.

I hope I am clear... is there a way to model quads with this constraint ?

Or if not, is there a way to make a quad planar, by specifying that 3 vertices should not move, and only the fourth should ?

Thanks in advance for your help

Why do you need planar quads? See blender.stackexchange.com/questions/56755/… — Duarte Farrajota Ramos, Commented Oct 8, 2017 at 21:39
Depending on the degree of subdivision, surface junctions etc all the quads can't be all planar by definition as some distortion will inevitably happen due to surface flow. Take for example default monkey without any sibdivisions, its quads are not planar and never will without subsurfing. If you try to make one planar, several neighbour ones will distort more and so on. Hence Make Planar Faces won't make them all ideally planar if mesh is too lowpoly. Regarding the constraint - no, I don't think it is and should be done. — Mr Zak, Commented Oct 8, 2017 at 23:04
Thanks for the feedback. I understand that it is not desirable nor even sometimes possible to make all quads planar in an existing model like the monkey. My objective is to build a model with planar planes, not make all quads planar in an already existing model. My question is whether there is a special trick to build a model with this constraint. — Pierre, Commented Oct 9, 2017 at 7:56

Jan Kadeřábek · Accepted Answer · 2017-10-10 18:14:56Z

I never needed that, but I think this workflow could do the job for you:

Creating new planar quads:

Make sure you have F2 addon enabled (it is enabled by default in Blender) by pressing CtrlAltU and navigating to Addons. Search for "F2" and enable it if it isn't already.
Extrude one vertex from existing polygon's edge so you get 2 edges prepared for the new quad
Select the middle vertex and move your mouse to the position you want to create a quad's opposite corner vertex
Press F - now the F2 addon creates a planar quad based on these 3 vertices

Make sure you have Transform Orientation set to Normal
Select a vertex and press G for move and then ShiftZ 2x to move on a plane perpendicular to Z normal of the face
This of course work only for corner vertices that are not part of other faces this is going to work when you are creating new polygons.
Alternatively, you can use Vertex Slide ShiftV that move's a vertex along edges so it also keeps a face planar. You can press Ctrl while sliding to be able to extend the sliding outside.

And as you have already noted, you can always press Spacebar > Make Planar Faces to convert the existing faces to planar ones.

Please accept the answer if it solves your problem :) I am happy I could help! — Jan Kadeřábek, Commented Oct 31, 2017 at 10:52