%D This example dates from late 2001, and ws probaby made for some \TEX\ related
%D meeting. It's a relative simple example that uses a few function from a general
%D \JAVASCRIPT\ preamble. In fact forcing the \type {FieldStack} code into the
%D is the only adaptation from \MKII\ to \MKIV\ (because we load on demand and here
%D the code is ude sindirectly).
%D
%D Nowadays we could layers instead which is probably a bit more ligthweight than
%D widgets. Also, we should actually synchronize the time but on the other hand, but
%D on the other hand, now it's a sort of stopwatch.

% \nopdfcompression

\starttext

\useJSscripts[fld]

\useJSpreamble[FieldStack]

\definepapersize
  [clock]
  [width=2.5cm,
   height=2.5cm]

\setuppapersize
  [clock][clock]

\setuplayout
  [header=0pt,
   footer=0pt,
   backspace=.25cm,
   topspace=.25cm,
   width=middle,
   height=middle]

\startJSpreamble stepper used now

    var state = 0 ;
    var more  = 0 ;
    var step  = 0 ;

    function step_clock() {
        try {
            if (more == 60) {
                more = 0 ;
                Walk_Field("more") ;
            } else {
            }
            more += 1 ;
            Walk_Field("clock") ;
            this.dirty = false ;
        } catch (e) {
        }
    }

    function start_clock() {
        try {
            if (state == 0) {
                step = app.setInterval ("step_clock()", 1000) ;
                step.count = 0 ;
                state = 1 ;
            } else if (state == 1) {
                app.clearInterval (step) ;
                state = 2 ;
            } else if (state == 2) {
                app.clearInterval (step) ;
                Reset_Fields("more") ;
                Reset_Fields("clock") ;
                Set_Field("more", "1") ;
                Set_Field("clock", "1") ;
                more = 0 ;
                state = 0 ;
            }
        } catch(e) {
        }
    }

    function stop_clock () {
        try {
            app.clearInterval(step) ;
        } catch(e) {
        }
    }

\stopJSpreamble

\definereference[StopClock] [JS(stop_clock)]
\definereference[StartClock][JS(start_clock)]

\setupinteraction
  [state=start,
   closeaction={StopClock,ForgetChanges},
   closepageaction={StopClock}]

\startreusableMPgraphic{common}
    drawoptions(withpen pencircle scaled 1mm withcolor .4white) ;
    fill fullsquare scaled 2.5cm ;
    drawoptions(withpen pencircle scaled 1mm withcolor .6green) ;
    draw fullsquare scaled 2.5cm ;
    drawoptions(withpen pencircle scaled 1mm withcolor .6red) ;
    draw fullcircle scaled 2cm ;
    drawoptions(withpen pencircle scaled 2mm withcolor .6yellow) ;
    for i=1 upto 12 :
        draw (0,1cm) rotated ((i-1)*(360/12)) ;
    endfor ;
\stopreusableMPgraphic

\startuseMPgraphic{clock}
    numeric stp ; stp := (\MPvar{n}-1)*(360/60) ;
    pair p ; p := (0,\MPvar{l}-.5mm) ;
    drawoptions(withpen pencircle scaled 1mm withcolor .6\MPvar{c}) ;
    draw (origin -- p) rotated -stp ;
    draw (p shifted (-2mm,-2.5mm)--p--p shifted (2mm,-2.5mm)) rotated -stp ;
    setbounds currentpicture to fullsquare scaled 2cm ;
    drawoptions(withpen pencircle scaled 2mm withcolor .6white) ;
    draw origin ;
\stopuseMPgraphic

\defineoverlay [common] [\reuseMPgraphic{common}]
\defineoverlay [start]  [\overlaybutton{StartClock}]

\setupbackgrounds
  [page]
  [background={common,start}]

\let\clocklist\empty
\let\morelist \empty

\dorecurse {60} {
    \appendtocommalist{step:#1}\clocklist
    \definesymbol
        [step:#1]
        [\useMPgraphic{clock}{n=#1,l=1cm,c=blue}]
    \appendtocommalist{more:#1}\morelist
    \definesymbol
        [more:#1]
        [\useMPgraphic{clock}{n=#1,l=.75cm,c=green}]
}

\definefieldstack
    [clock]
    [\clocklist]
    [width=2cm,height=2cm,offset=overlay,frame=off]

\definefieldstack
    [more]
    [\morelist]
    [width=2cm,height=2cm,offset=overlay,frame=off]

\starttext

    \startoverlay
        {\fieldstack[more]}
        {\fieldstack[clock]}
    \stopoverlay

\stoptext