undo does not return a point to its original position

[Chao-Kuei Hung]

Open the attached file. Notice that the angle is currently 53 deg. Drag point V0 around the circle. Click the "undo" button. It returns to a different position.

DrGeo 15.12a on lubuntu 15.04

[Chao-Kuei Hung (ckhung0)]

Got the serious bug of #1539835 again!

I continued from g3.fgeo of this bug report. Line "G2"-"O", Line "O"-"V0", and point "G2" are hidden. A free point on the x-axis (actually line "Ha"-"Hb") is created. A vertical line at this point is created. The vertical line is intersected with line "directrix" to create a point. Then the file is saved as g4.fgeo, and g4.fgeo goes lunatic.

[hilaire (hilaire-fernandes)]

Indeed the undo/redo command is not symmetrical for point constrained on line.

The move command comes with a displacement vector attribute, the do command-action translate with vector, the undo command action translate with -vector. But for point constrained on a line it is not symmetrical.

Possible solution: define a specific move command for constrained point on line. Its attribute will be the point curvilinear abscissa.

I don't think this problem is related with the #1539835 bug.