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[a-k-]

For the general case:
1. y = ax+b
2. (x%1 - 0.5)² + (y%1 - 0.5)² < 0.1

Translate the line to get rid of the two 0.5's.
"Inflate" it so that it has a thickness of 2*sqrt(0.1).
Let y1 and y2 be the upper and lower outlines of the thick line.

For any integer x0:
- For any integer y0 in the open interval (y1, y2):
- - (x0, y0) is the origin of a circle intersecting the translated line
- - Calculate its 2 intersections with the translated line
- - Translate back to the original coordinates system

Edit: more details

[gimymblert]

Thanks, there is some interesting ideas.

I forgot to specify I was trying to get rid of for loop because shader... I guess this is no longer a quick question and I should open a thread ... I'm looking for a result in form of kf(x), in which k give the kth hit, as a generalization of ddx algorithm, but on "concave" primitive instead of line or plane.

[gimymblert]

I made a thread: probably not solvable ?
https://forums.tigsource.com/index.php?topic=74410.0

I solved first hit before applying my wrapping trick, but once the ray wrapped vertically (using minor axis symmetry to select the vertical), finding other hit for n wrap in fixed step (no loop aka no raymarch) seems like a tall order.