the X coordinate of the first control point
the Y coordinate of the first control point
the X coordinate of the second control point
the Y coordinate of the second control point
the X coordinate of the end of the curve
the Y coordinate of the end of the curve
Adds a cubic Bézier spline to the path from the current point to position (x3, y3) in user-space coordinates, using (x1, y1) and (x2, y2) as the control points. After this call the current point will be (x3, y3). If there is no current point before the call to cairo_curve_to() this function will behave as if preceded by a call to cairo_move_to(cr, x1, y1).