cairo-rel-curve-to (cr dx1 dy1 dx2 dy2 dx3 dy3)

cr -- a cairo-t context
dx1 -- a double float x offset to the first control point
dy1 -- a double float y offset to the first control point
dx2 -- a double float x offset to the second control point
dy2 -- a double float y offset to the second control point
dx3 -- a double float x offset to the end of the curve
dy3 -- a double float y offset to the end of the curve

Relative-coordinate version of the cairo-curve-to function. All offsets are relative to the current point. Adds a cubic Bézier spline to the path from the current point to a point offset from the current point by (dx3, dy3), using points offset by (dx1, dy1) and (dx2, dy2) as the control points. After this call the current point will be offset by (dx3, dy3).

Given a current point of (x, y),

(cairo-rel-curve-to cr dx1 dy1 dx2 dy2 dx3 dy3)  

is logically equivalent to

(cairo-curve-to cr (+ x dx1) (+ y dy1)
                   (+ x dx2) (+ y dy2)
                   (+ x dx3) (+ y dy3))  

It is an error to call this function with no current point. Doing so will cause cr to shutdown with a status of :no-current-point.