Priority for constraints

[adamchalmers]

Problem

ZDS users will have some explicit constraints (e.g. "these two lines are the same length"). Other constraints are kinda implicit, e.g. when the user drags a point with their mouse, they're implicitly adding a constraint that the point should be coincident with the mouse's position. But if that would make the system unsolvable, we should probably just use the mouse location as a best guess, not as a constraint.

Right now ezpz has no way to say "try to satisfy all these constraints, and if you can, then also try adding this mouse constraint."

Solution

• User can specify a constraint's priority as a u32. 0 is highest priority, larger numbers are lower priority.
• First, ezpz solves for all the highest-priority constraints (i.e. priority 0)
• If a solve fully satisfies all attempted constraints, then add the next lowest-priority constraints (e.g. priority 1)
• Repeat until a system could not be fully satisfied.

As a first try, we'd set all explicit constraints to P0, and then the mouse drag constraint as P1.

[Irev-Dev]

from most- to least-recently-dragged.

A side note really, because I don't have a problem with a u32 priortity system, but I think in practice we wont end up using "most- to least-recently-dragged", because we would have to reflect this in the kcl, and previous dicussion had the consensus the best way to reflect where the user dragged in kcl, was just to update all of the vars to the solved values.

But might still be useful for reflecting most recently selected, in the case of dragging multiple segments

[adamchalmers]

Edited to remove the other mouse drags, p2/3/4 etc.