gtk:render-line (context cr x0 y0 x1 y1)

context -- a gtk:style-context object
cr -- a cairo:context-t context
x0 -- a number, coerced to a double float, with the x coordinate for the origin of the line
y0 -- a number, coerced to a double float, with the y coordinate for the origin of the line
x1 -- a number, coerced to a double float, with the x coordinate for the end of the line
y1 -- a number, coerced to a double float, with the y coordinate for the end of the line

Renders a line from (x0,y0) to (x1,y1).