colourwheel.php source code

This is the whole of the PHP script that drew the 2008 colour wheel: 64 lines, one section at a time, each with a plain-language explanation. The idea in one sentence: every colour name is printed in its own colour, at an angle set by its hue and a distance from the centre set by its value (the “V” of HSV).

The script needs PHP with the PDFlib extension and a MySQL table of colour names. Colourwheel was written for PHP 5, most likely 5.2.x, and MySQL 5.0 or 5.1 (5.5 also works), in 2008.
Download the plain script · Back to the colour wheel

Orientation notes

The file opens with the author's own reminder about PDFlib's text rotation: the angle is absolute (not relative to the previous text), positive means anticlockwise, and 0 points along the horizontal. Everything below leans on that convention.

<?php

//rotate is absolute
//positive is anticlockwise
//rotate starts at horizontal.

Settings

The page is a 2000 × 2000 point square and every colour name is set in 12 point type. Change these two numbers to get a bigger or denser wheel.

$size = 2000;
$fontsize=12;

Start a PDF in memory

new PDFlib() creates a PDF writer from the PDFlib extension. begin_document("","") with an empty filename means “build the file in memory”, which is why the script fetches the bytes with get_buffer() at the end. set_info fills in the PDF's metadata fields.

$pdf = new PDFlib();
$pdf->begin_document("","");

$pdf->set_info("Creator","colourwheel.php");
$pdf->set_info("Author","Telyn Z.");
$pdf->set_info("Title","Colour Wheel");

Page, background and font

Opens a single page the size of the square, then fills a rectangle covering all of it. The commented-out setcolor line is how the author's note says to uncomment for a black background; PDF's default fill colour is black anyway, so the published wheel is coloured text on black either way. Helvetica is one of the 14 standard PDF fonts, so nothing needs embedding.

$pdf->begin_page_ext($size,$size,"");
//$pdf->setcolor("fill","rgb",0,0,0,0); //uncomment this line to get a black background
$pdf->rect(0,0,$size,$size);
$pdf->fill();

$font = $pdf->load_font("Helvetica","iso8859-1","");
$pdf->setfont($font,$fontsize);

Geometry: centre and radius

Defines the circle. ($ox, $oy) is the centre of the page. $radius is 80% of the half-width (800 points), leaving a 10% margin so the longest names at the rim do not run off the page. DEG_TO_RAD is the usual π/180, as PHP's trig functions take radians but the angle arithmetic below is easier in degrees.

define("DEG_TO_RAD",M_PI/180);
//define the origin
$ox = $size/2;
$oy = $ox;
$radius = $ox - $size/10;

Fetch the colour names

Connects to a MySQL database called colourwheel and pulls every row of the colours table: the name people gave a colour, its RGB (for painting the text) and its HSV (for placing it). The host, user and password here are placeholders for a local Docker setup, not real credentials. The table was loaded from the Dolores Labs colour-names data set, which is not part of this repository. The loop then handles one colour name per pass.

$mysql = new MySQLi("mysql","root","password","colourwheel");
$result = $mysql->query("SELECT name,red,green,blue,hue,saturation,value FROM colours");
while($colour = $result->fetch_array()) {

Hue becomes an angle

Hue, saturation, value and RGB are all stored as fractions from 0 to 1. Hue 0 starts at 12 o'clock (−90°) and each extra hue × 360 degrees is subtracted, so as hue increases the name moves anticlockwise round the wheel.

    //Each colour's hsv & rgb are between 0 and 1.
    $angle = -90; //this puts the angle at the top right now.
    $angle -= ($colour['hue']*360); //puts the angle in the right place.

Value becomes a distance

Measures how wide the name is when printed, then decides how far from the centre to anchor it: value × radius (dark colours near the middle, bright ones near the rim), plus half the text width as a nudge so long names do not pile up in the middle. The angle is also converted to radians here.

    $width = $pdf->stringwidth($colour['name'],$font,$fontsize);

    $distance = ($width/2) + ($colour['value']*$radius); //offset text length.
    $radians = $angle*DEG_TO_RAD;

Polar to page coordinates

Ordinary trigonometry: cos and sin turn (angle, distance) into an x and y offset from the centre. PDF's y axis points up, so the y offset is flipped ($oy - $y) and both values are finally shifted by the centre point.

    $x = cos($radians)*$distance;
    $y = sin($radians)*$distance;
    $y = $oy-$y;
    $x += $ox;

Draw the name

Sets the fill colour to the name's own RGB colour (the last 0 is an unused fourth component, as PDFlib's setcolor takes up to four), then fit_textline places the text at (x, y) rotated by -$angle. That rotation is the same direction as the name's position, so each name reads outwards along its own spoke of the wheel.

    $pdf->setcolor("fill","rgb",$colour['red'],$colour['green'],$colour['blue'],0);
    $pdf->fit_textline($colour['name'],$x,$y,"rotate=".-$angle);
}

Finish the PDF

Closes the page and the document, copies the finished file out of PDFlib's memory into a PHP string, and frees the PDFlib object.

$pdf->end_page_ext("");

$pdf->end_document("");

$buffer = $pdf->get_buffer();
$length = strlen($buffer);
$pdf->delete();

Send it to the browser or file

The commented-out header() lines would turn this into a web page that serves the PDF inline (note $len there should be $length). As written, the script just echoes the raw PDF bytes to standard output, so on the command line you would run php colourwheel.php > colourwheel.pdf.

# header("Content-Type: application/pdf");
# header("Content-Length: $len");
# header("Content-Disposition: inline; filename=colourwheel.pdf");

echo $buffer;

?>

colourwheel.php, annotated