The cpdf_curveto() function
draws a Bezier curve from the current point to the point (x3,
y3) using (x1, y1) and (x2,
y2) as control points.
The optional parameter
mode determines the unit length. If it's 0 or
omitted the default unit as specified for the page is used.
Otherwise the coordinates are measured in postscript points
disregarding the current unit.
See also cpdf_moveto(),
cpdf_rmoveto(),
cpdf_rlineto(),
cpdf_lineto().