Color wheel

Color wheel is a draft programming task. It is not yet considered ready to be promoted as a complete task, for reasons that should be found in its talk page.

Task

Write a function to draw a color wheel completely with code.

This is strictly for learning purposes only. It's highly recommended that you use an image in an actual application to actually draw the color wheel   (as procedurally drawing is super slow). This does help you understand how color wheels work and this can easily be used to determine a color value based on a position within a circle.

GML

<lang GML> for (var i = 1; i <= 360; i++) {

   for (var j = 0; j < 255; j++) {

       var hue = 255*(i/360);
       var saturation = j;
       var value = 255;

       var c = make_colour_hsv(hue,saturation,value);
       
       //size of circle determined by how far from the center it is
       //if you just draw them too small the circle won't be full. 
       //it will have patches inside it that didn't get filled in with color
       var r = max(1,3*(j/255));

       //Math for built-in GMS functions
       //lengthdir_x(len,dir) = +cos(degtorad(direction))*length;
       //lengthdir_y(len,dir) = -sin(degtorad(direction))*length;
       draw_circle_colour(x+lengthdir_x(m_radius*(j/255),i),y+lengthdir_y(m_radius*(j/255),i),r,c,c,false);
   }

} </lang>

Perl 6

Works with: Rakudo version 2016.08

<lang perl6>use Image::PNG::Portable;

my ($w, $h) = 300, 300;

my $out = Image::PNG::Portable.new: :width($w), :height($h);

my $center = $w/2 + $h/2*i;

color-wheel($out);

$out.write: 'Color-wheel-perl6.png';

sub color-wheel ( $png ) {

   for ^$w -> $x {
       for ^$h -> $y {
           my $vector    = $center - $x - $y*i;
           my $magnitude = $vector.abs * 2 / $w;
           my $direction = ( π + atan2( |$vector.reals ) ) / τ;
           $png.set: $x, $y, |hsv2rgb( $direction, $magnitude, $magnitude < 1 );
       }
   }

}

sub hsv2rgb ( $h, $s, $v ){ # inputs normalized 0-1

   my $c = $v * $s;
   my $x = $c * (1 - abs( (($h*6) % 2) - 1 ) );
   my $m = $v - $c;
   my ($r, $g, $b) = do given $h {
       when   0..^(1/6) { $c, $x, 0 }
       when 1/6..^(1/3) { $x, $c, 0 }
       when 1/3..^(1/2) { 0, $c, $x }
       when 1/2..^(2/3) { 0, $x, $c }
       when 2/3..^(5/6) { $x, 0, $c }
       when 5/6..1      { $c, 0, $x }
   }
   ( $r, $g, $b ) = map { (($_+$m) * 255).Int }, $r, $g, $b;

}</lang>

Until local image uploading is re-enabled, see Color-wheel-perl6.png

zkl

A color square - I just fill a square with the color wheel, it could be clipped to a circle if needed. Each point in the square is converted to polar coordinates, the angle is hue and the radius is saturation (which is scaled by the distance from the pole).

Uses the PPM class from http://rosettacode.org/wiki/Bitmap/Bresenham%27s_line_algorithm#zkl <lang zkl>var w=300,h=300,out=PPM(w,h); colorWheel(out); out.writeJPGFile("colorWheel.zkl.jpg");

fcn colorWheel(ppm){

  centerX,centerY:=ppm.w/2,ppm.h/2;
  d:=centerX.toFloat().hypot(centerY);
  foreach x,y in (w,h){
     v,hue:=(x - centerX).toFloat().toPolar(y - centerY); 
     if((hue = hue.toDeg())<0) hue+=360;  // (-pi..pi] to [0..2pi)
     s:=v/d;  // scale saturation zero at center to 1 at edge
     ppm[x,y]=hsv2rgb(hue,1.0,s);
  }

}

fcn hsv2rgb(hue,v,s){ // 0<=H<360, 0<=v(brightness)<=1, 0<=saturation<=1 // --> 24 bit RGB each R,G,B in [0..255]

  to24bit:=fcn(r,g,b,m){
     r,g,b=((r+m)*255).toInt(),((g+m)*255).toInt(),((b+m)*255).toInt();
     r*0x10000 + g*0x100 + b
  };
  c:=v*s;
  x:=c*(1.0 - (hue.toFloat()/60%2 - 1).abs());
  m:=v - c;
  if     (0  <=hue< 60) return(to24bit(c,  x,  0.0,m));
  else if(60 <=hue<120) return(to24bit(x,  c,  0.0,m));
  else if(120<=hue<180) return(to24bit(0.0,c,  x,  m));
  else if(180<=hue<240) return(to24bit(0.0,x,  c,  m));
  else if(240<=hue<300) return(to24bit(x,  0.0,c,  m));
  else			 return(to24bit(c,  0.0,x,  m));

}</lang> Until local image uploading is re-enabled, see this image.