clock.ps

%!

% Draws an animated clock.
% Author: Dakota Schneider, dakota@lclark.edu
% Usage: gs midterm2_clockwithsleep.ps
% Options: None.
% Configuration: can set target frame length or calculate from target framerate.


% draws a clock
% taken from: http://doc.novsu.ac.ru/oreilly/web/cgi/ch06_02.htm#CGI-CHP-6-SECT-2.4
% modified to display seconds
/clock
% - clock -
{
    gsave

    % we get the time from the %Calendar% device, available in ghostscript env
    % thanks to https://en.wikibooks.org/wiki/PostScript_FAQ#How_to_get_date_and_time.3F
    (%Calendar%) /IODevice resourcestatus {
        pop pop (%Calendar%) currentdevparams
        dup /Running get {
            dup /Year get /year exch def
            dup /Month get /month exch def
            dup /Day get /day exch def
            dup /Hour get /hour exch def
            dup /Minute get /min exch def
            /Second get /sec exch def
        } {
            (Clock/calendar is present but not running.\n) print
        } ifelse
    } {
        (No clock/calendar present.\n) print
    } ifelse

    % configuration
    /max_length     150 def
    /line_size      1.5 def
    /marker         5 def

    % calculated values
    /center          { 0 dup } def
    /radius          { max_length 2 div } def
    /hour_segment    { 0.50 radius mul } def
    /minute_segment  { 0.80 radius mul } def
    /second_segment  { 0.90 radius mul } def

    % some color constants
    /red             { 1 0 0 setrgbcolor } def
    /green           { 0 1 0 setrgbcolor } def
    /blue            { 0 0 1 setrgbcolor } def
    /black           { 0 0 0 setrgbcolor } def
    /white           { 1 1 1 setrgbcolor } def

    /hour_angle {
        hour min 60 div add 3 sub 30 mul
        neg
    } def
    /minute_angle {
        min sec 60 div add 15 sub 6 mul
        neg
    } def
    /second_angle {
        sec 6 mul
        neg
    } def


    line_size setlinewidth

    % draw face (covers up previous drawing)
    center radius 1.1 mul 0 360 arc white fill
    center radius 0 360 arc black stroke

    % draw
    black
    1 1 12 {
        pop
        radius marker sub 0 moveto
        % marker 0 rlineto red stroke
        marker 0 rlineto stroke
        30 rotate
    } for

    % hour hand
    center moveto
    hour_segment hour_angle cos mul
    hour_segment hour_angle sin mul
    lineto green stroke

    % minute
    center moveto
    minute_segment minute_angle cos mul
    minute_segment minute_angle sin mul
    lineto green stroke

    % second
    center moveto
    second_segment second_angle cos mul
    second_segment second_angle sin mul
    lineto red stroke
    % second hand cap
    center line_size 2 mul 0 360 arc red fill

    grestore
} def

/sleep
% <int:milliseconds> sleep -
{
    % note: while realtime rolls over to 0 when too large,
    % we ignore this possibility as 32-bit int can contain
    % ~50 days worth of milliseconds

    % nothing to do if we get a negative value
    dup 0 gt {
        % delta
        realtime
        % delta start
        add
        % end

        % busy wait until
        {
            % end time < current time
            dup realtime lt {
                exit
            } if
        } loop
    } if
    % clean up
    pop
} def


%
% Draw FPS
%
% need to know where the upper right corner is
/pagewidth  612.0 def  % standard for US Letter size paper
/pageheight 792.0 def

% looks familiar
/prnum {
    ( ) show
    100 string % create a string of 20 characters
    cvs % convert object to string :   object string cvs  =>  string
    show
} def

% framerate calculations
/lastframe realtime def
/framerate 0 def
/drawfps
% - drawfps -
{
    % draws current framerate in the upper right corner of the page

    gsave
        % display setup
        pagewidth 48 sub pageheight 32 sub translate

        % black background
        0 0 0 setrgbcolor
        0 0 moveto
        0 12 lineto
        48 12 lineto
        48 0 lineto
        closepath
        fill

        % set up text color and position
        0 0 moveto
        1 1 1 setrgbcolor
        /Helvetica findfont 12 scalefont setfont

        % compute framerate, average with previous value
        realtime lastframe sub % frame delta in ms
        dup 0 eq { 1 } if % handle edge case on first loop
            % realtime is interpreter uptime, so running this on
            % a camputer can have issues on the first loop where we've
            % *just recently* set lastframe and realtime returns the same value
        1000 exch div % frames per second
        % rolling average for a tiny bit of stability
        framerate add 2 div /framerate exch def
        % display
        framerate prnum
    grestore

    /lastframe realtime def
} def


% framerate cap
/target_framerate 30 def
% how long should we wait per frame? (milliseconds)
/target_frametime 1000 target_framerate div def
% uncomment below for uncapped
% /target_frametime 0 def


% almost like real programming
/main
% - main -
{
    {
        % update last frame render time
        /starttime realtime def

        % provide two minutes of operation before exiting
        starttime 1000 60 mul 2 mul gt { exit } if


        % do the thing
        gsave
            300 300 translate
            clock
        grestore


        % draw FPS on top
        drawfps

        % last but not least, flush this frame
        % thanks to http://stackoverflow.com/a/8396072/362042
        flushpage

        % busy wait until it's time to draw the next frame
        starttime target_frametime add realtime sub sleep
    } loop
} def

% let's boogie
main

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