stroke
Sets the thickness of the pen used by the paint to outline the shape. A stroke-width of zero is treated as "hairline" width. Hairlines are always exactly one pixel wide in device space (their thickness does not change as the canvas is scaled). Negative stroke-widths are invalid; setting a negative width will have no effect.
Return
zero for hairline, greater than zero for pen thickness
See also
https://fiddle.skia.org/c/@Paint_setStrokeWidth
Returns the thickness of the pen used by Paint to outline the shape.