The cpdf_circle() function draws a circle with center at point (x_coor, y_coor) and radius radius. 成功回傳TRUE失敗回傳FALSE。
The optional parameter mode determines the unit length. If it is 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_arc().