cpattern:CurveTo(x1, y1, x2, y2, x3, y3)
x3, y3) in pattern-space coordinates, using
(x1, y1) and (x2, y2) as the control points.
If the current patch has no current point before the call to
cpattern:CurveTo(), this function will behave as if
preceded by a call to cpattern:MoveTo() with x1 and y1
as parameters.
After this call the current point will be (x3, y3).
Note: If the pattern is not a mesh pattern then it will be put
into an error status with a status of
#CAIRO_STATUS_PATTERN_TYPE_MISMATCH. If the pattern has no current
patch or the current patch already has 4 sides, it will be
put into an error status with a status of
#CAIRO_STATUS_INVALID_MESH_CONSTRUCTION.