Interesting debate. Here's my 2p.
When the nozzle turns into a corner it's accelerating independently in X and Y directions according to the respective stepper motors.
Steeper corners require BOTH more braking (deceleration = slowing / stopping of the current direction of movement) and acceleration (starting off in a new direction of movement).
My hunch is that ringing type problems are not created by the acceleration into the new direction, but the deceleration from the old one (if you'll forgive the distinction).
According to this way of looking at things, the job of a "look ahead" system would be to calculate the amount of the present extruder velocity that must be eliminated by the exit of the curve, then to pre-emptively slow the extruder before the curve actually begins (so to speak).
Thus gentle curves will not provoke much in the way of pre-emptive slowing (of the current direction of movement, whatever combination of X and Y that may be), but right angle bends an awful lot.
Is it possible from the gcode with a suitably modest amount of computation to estimate how much deceleration of the current velocity will be demanded by upcoming moves?
