Awhile ago MugenCity posted that FSlateDrawElements::MakeLines had broken AA ([see this post]). The bug report for that (UE-30471) has been marked as fixed and that fix was included in 4.13. While that fix does seem to have fixed the case given in the original post, it doesn’t seem to actually have fixed the problem in the general case.
The problems I’m having with FSlateDrawElements::MakeLines are shown below. The first image shows the broken line (in red) and what the line should look like (in green) separated. The second image shows the two lines overlaid on top of each other, so you can see what the red line should look like. The broken (red) line has a render transform that scales it by 10x in order to make it the same size as the good (green) line.
The broken line (red) and the good line (green) overlaid so you can see what the broken line should look like.
The two lines were created by just creating two new widget blueprints and overriding the OnPaint functions for each.
The blueprint for the OnPaint function of the broken (red) line is shown below.
And the following blueprint is for the OnPaint function of the good (green) line, which is the same, just with the points scaled by 10x.
With the above example, it seems like the problem is definitely related to the distance between the non-transformed points on the line, and all the other times I’ve experienced the problem is when the points on the line have been fairly close together (though certainly not unreasonably close).