Posted by AlPal on Sep 04, 2021; 3:56am
URL: https://forum.librecad.org/Drawing-a-site-plan-using-LibreCAD-tp5720964p5720999.html

I have been able to narrow down the range of possibilities for this problem. Firstly, I plugged a mouse into the USB port. This made no difference to the problem whatsoever. So the built-in trackpad is not the problem.

When the Parallel function is performing correctly, parallel lines appear on one or other side of the original line, depending on the side from which the original line is approached. The parallel function works when the original line is horizontal or vertical. However, the parallel lines are only displayed on one side of the original line, irrespective of the side from which the original line is approached. The suggests that the original line is correctly located but the direction of approach is not being correctly detected. The side of original line on which the parallels appear depends on the direction in which the original line is drawn. If the original vertical line is drawn downwards the parallel lines appear the left. If it is drawn upwards the parallel lines appear to the right of the original line.

Although the problem appears with both version 2.2.0 rc2 and version 2.1.3 of LibreCAD. However, when LibreCAD 2.2.0 rc2 is run on an old Mac Mini running under High Sierra, the software runs normally. There seems to be another difference. When the function is performing normally, the parallel lines appear as the cursor approaches the original line. However, on my MacBook Air the parallel lines only appear when the cursor is exactly over the line.

The problem seems to be related to computation of the position of the cursor in relation to the original line. The a fact that the Parallel function works correctly on an older version of the OS but not on the most recent version points to a possible explanation. Between High Sierra and Big Sur Apple changed from 32-bits to 64-bits for its operating systems. For a period both 32 bits and 64 bits were supported but Big Sur can only support 64-bit applications. In the intervening period software developers had to modify their applications to run on 64-bit OSs. Could the conversion to run on 64-bit OSs have introduced an obscure computation bug? I have yet to think of a way of ruling this possibility out.