Snap to fish eye assistant behaves strange close to the center line


I have an assistant tool setup with two horizontally aligned vanishing points and one vertically aligned fish eye. Snapping works as expected almost everywhere except for regions close to the center line of the fish eye assistant:

  • When I want to draw along the vertical fish eye center line, it mostly snaps to one of the other two assistants although their directions are almost perpendicular to what is suggested by my cursor strokes.
  • When it finally snaps, it behaves very strange. It doesn’t follow the pointer position but is very sensitive to perpendicular movements instead. If I move the mouse only slightly to the left or right, the brush stroke quickly follows the guidance lines up or downwards receding from the cursor position. I.e., the cursor’s y-coordinate is much more sensitive to the relative x-coordinate of the mouse pointer than to the y-coordinate. It feels divergent.
  • When the center line is accidentally crossed by the cursor while drawing a line very close to it, the brush stroke goes all the way up to the reference point and down again on the other side.

I guess, all this naturally results from a conformal (?) mapping of the fish eye assistant but it doesn’t feel like I would expect. I don’t know about the implementation but might it be easy to fix by making it more sensitive to the direction that is parallel to the reference line of the fish eye assistant?

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Hello and welcome to the forum :slight_smile:

Even with an isolated fish-eye, the snapping along the centre line is erratic, jumpy and quite wrong. This may be because on the centre line there are also two fish-eye curves as candidates for snap targets.