When I move this path, three of the handles shift by 1 unit in the x and/or y directions. To check whether it might be a font conversion issue (from UFO), I created a new font and drew a fresh simple path, and the behaviour is still there. This is with Glyphs 2.5.2 (1161), confirmed in cutting edge 2.5.2 (1163), on macOS 10.12.6.
In the screenshot, I have copied, pasted and moved the path to show a comparison with the original, but it also happens when just moving the original (via keyboard shortcuts or Wacom tablet). The handles are at integer coordinates before the move, so it doesn’t seem to be a simple rounding issue. Sample Glyphs file attached.
The green connector tries to align the two handles anew. Aligning diagonally on a grid is a constant rounding problem. You could try turning the points into blue corner connectors before moving, or move with the arrow keys only.
This is happening via arrow keys, when all the on-curve points and handles are already (or seem to be) at integer coordinates, and I move the whole path (so not moving a subset of nodes or changing the path in any way). If all the points are at integer coordinates, and I move the path by an integer number of units, is rounding involved? I would understand if I was scaling or rotating, then rounding would be an issue.
It doesn’t seem practical to change a number of nodes from green to blue before moving just in case their handles get changed, and then change them back to green, when I’m just wanting to shift a path. Is there any way this could be improved?
I can send you separately my real-life example where the effect of the change is quite significant.
On the sample file, if you Select All, Copy, Paste and Command+RightArrow followed by Command+LeftArrow, do you see the effect? I’m using Glyphs 2.5.2 (1161), confirmed in cutting edge 2.5.2 (1163), on macOS 10.12.6.
I should say that, although the sample above shows a minimal impact of the changed handles, the real-life case produced a significant overlap between a stem and a counter, such that the counter had a noticeably flat edge to it
This is the exact same problem I encountered previously, discussed here:
In my case I worked around the problem by using mekkablue’s plugin Show Coordinates of Selected Nodes and manually making sure the coordinates of both long and short handles matched. A lot of work but well worth it – no more snapping and messing up curves.
I also switched to a 2000 UPM which made things a lot easier when it came to matching coordinates.
