@Petrichor is correct. The problem is accumulation of rounding error in the Set Position steps.
First, 1 long line is drawn between the 2 points. That part of the line is drawn accurately (since you rounded the Last Touched locations to be exact points on the graph). Subsequently, the remainder of the line is drawn in small steps. Each one of those small steps accumulates a small error as the Set Position block rounds the position to the nearest pixel.
There’s multiple approaches to fixing the issue
- As Petrichor said, implement 2 new variables to track the X & Y locations of each small step more precisely. I’d speculate that this is a more complicated approach.
- Calculate where the line crosses the outer bounds of the graph. Draw 1 single line between these two points. Those points will still get rounded by the Set Position to the nearest pixel, but that won’t be noticeable. This is what I’d recommend.