"Face" in T-spline: free draw 4th vertex in plane defined by 3 placed vertices

[dunderhead]

For making faces   allow fourth vertex to be freely placed. This should be the default I'd suggest! There's a perfectly natural plane defined for this purpose: the three already placed vertices. 

The alternative: battling with extrusions with local coordinate system that often seems the wrong one is cumbersome.

[keqingsong]

Hey Dunderhead, thanks for the suggestion. I'm a bit confused on what you're asking - the Face command seem to allow this to happen already? 

[dunderhead]

Kequing, neat animation, thanks for your interest!

The problem is that when I free-sculpt in 3D there just isn't any useful pre-defined plane available (construction, origin planes, ...). That's most of the time: I don't have that plane!

The image enclosed shows a planar face in grey that I've just constructed. Here I'm looking at the top a structure, which I've started to roof. The free corner d (top-right) is set on the plane naturally defined by the three other points a, b, and c.  It (the point d) appears suspended in free air, but what you can't see is that the quad abcd is actually planar (wrt CVs)! I cheated to do this because the 'face' command doesn't allow me to use the natural plane for setting the corner vertex d.

In my work process, I'll edit the free corner d next to lift it out of the plane defined by the three other corners, then the quad abcd becomes non-planar as many T-spline faces tend to be. In this way I build more 3D shape and this new vertex will then help define new planes. And so on... But the face command is a straight-jacket in its current form: it forces me use either snapping or a predefined plane -- I can't work from any naturally defined planes in the T-spline. Extrusions are better in this way, but they entail clean-up work, merging vertices and edges and that's not so pleasant.

Let me just tie this together with my other proposals. I suggest that if I pre-select edges ab and bc, then the 'face' command will automatically direct me to complete the quad (that's filed here: another proposal). Combining the two ideas, whenever I select two edges and click 'face', I'll be directly asked to place the 4th vertex, making a planar face --  that should feel simple and natural!

(One could go even further and suggest just one more click for then adjusting the Z-coordinate of the new vertex, relative to the planar face. With the new multiple viewports, that may make direct 3D-sculpting much easier!)

Another little idea to ponder: if I click the 4th corner onto an existing corner, then a triangle is generated, not a degenerate quad (filed here).

And finally, the face command shouldn't by default ever draw a twisted quad (as seen in the active viewport), that's filed here.

[colin.smith]

I'll admit that this is a pain sometimes, but it isn't a high priority. 
I'm going to put this in our backlog to see if we can come up with a solution.

Release date TBD.