USING: arrays kernel math prettyprint sequences
ui.gadgets.worlds ui.gadgets.worlds.null opengl.gl ;
IN: dragon

: zig ( p1 p2 -- p1 pI p2 )
    [ [ first2 ] bi@
      [ [ rot swap + swap ] dip - + 2 / ] 4keep
      [ rot + swap ] dip + + 2 / 2array
    ] 2keep [ swap ] dip ;

: zag ( p1 p2 -- p1 pA p2 )
    [ [ first2 ] bi@
      [ [ rot swap + swap ] dip + - 2 / ] 4keep
      [ rot swap - swap ] dip + + 2 / 2array
    ] 2keep [ swap ] dip ;

: dragon' ( p1 p2 p3 d -- seq )
    dup zero? [
        2drop 2array
    ] [
        1 - swap dupd swap [ dupd swap ] 2dip ! p1 p2 d p2 p3 d
        [ zig ] 4dip [ zag ] dip ! p1 pI p2 d p2 pA p3 d
        [ dragon' ] 4dip dragon' ! p1 pI p2 d dragon' / p2 pA p3 d dragon'
        append
    ] if ;

: dragon ( -- x )
    "dragon" null-window [
        GL_LINE_STRIP glBegin
        100 200 [ dup 2array ] bi@ zig 2 dragon'
        [ first2 glVertex2d ] each
        glEnd ] into-window  ;

MAIN: dragon