Hacking at 0300

This is something I didn't know about: Prism, the syntax highlighter I use, is available from a few free CDN's, so I don't have to host it. Cool!

I'm not a designer, and I've never been happy with the color scheme for kavanot.name, so I decided to try something new. I use scssphp with scssphp server (and yes, you need both) to generate the CSS, and it allows variables, so I can do:

$hue = 250;
$saturation = '40%';
$textcolor: hsl($hue, $saturation, 10%);
$displaytextcolor: hsl($hue, $saturation, 40%);
$backcolor: hsl($hue, $saturation, 95%);
$bordercolor: hsl($hue, $saturation, 90%);
$deepbackcolor: hsl($hue, $saturation, 85%);

to make all the colors a variation on one single color. And I like that. But what color? Fortunately, scssphp allows for importing variables, so my `styles.php` includes:

setcookie('hue', $_GET['hue'], time()+12*60*60*24*30, '/'); // one year expiration
setcookie('saturation', $_GET['saturation'], time()+12*60*60*24*30, '/'); // one year expiration

$scss = new Compiler();
$scss->setVariables(array(
	'hue' => intval($_GET['hue']),
	'saturation' => intval($_GET['saturation']).'%',
));

instead of the in-file $hue = 250; $saturation = '40%';. Now I can include those values in the URL for the stylesheet itself,
and the cookies mean that I don't have to write it each time.

To get the query variables to the stylesheet, I have to pass them from the main page:

	<link rel="stylesheet" id=mainstylesheet type="text/css" href="/css/style.php/style.scss?hue=<?=$_GET['hue']?>&saturation=<?=$_GET['saturation']?>" />

(I am ignoring the input sanitization you need to avoid XSS. intval is your friend here!)

But retyping http://kavanot.name?hue=250&saturation=40 with minor variations is a pain. Can I make it interactive? Yes, with a Javascript
color picker. <input type=color /> is supported in all the major browsers, so I can do:

var colorPicker = $('input[type=color]');
let baseHSL = getBaseHSL(); // get the body color as [hue, saturation, lightness]
baseHSL[2] = 50; // start with a color that can be easily seen, 50% lightness
colorPicker.val(hsl2hex(...baseHSL)); // set the initial value

const stylesheet = $('#mainstylesheet')[0];

colorPicker.on('input', function(){
	let [h, s] = hex2hsl(this.value);
	// change the stylesheet href and the styles change on the fly!
	stylesheet.href = stylesheet.href.replace(/hue=\d+/, `hue=${h}`).replace(/saturation=\d+/, `saturation=${s}`);
});

function getBaseHSL(){
	// getComputedStyle.color is rgb(r,g,b)
	let [, r, g, b] = /(\d+),\s*(\d+),\s*(\d+)/.exec(window.getComputedStyle(document.body).color);
	return rgb2hsl (r, g, b);
}

Now I need the functions rgb2hsl, hex2hsl and hsl2hex to convert between the various color spaces. Luckily,
Jon Kantner has done the work for me.

function hex2hsl(hex){
	let [, r, g, b] = /#(..)(..)(..)/.exec(hex);
	return rgb2hsl (+('0x'+r), +('0x'+g), +('0x'+b));
}
	
function rgb2hsl (r, g, b){
	// convert to fractions
	r = r/255;
	b = b/255;
	g = g/255;

	// find greatest and smallest channel values
	const cmin = Math.min(r,g,b);
	const cmax = Math.max(r,g,b);
	const delta = cmax - cmin;
	let h;

	// calculate hue
	if (delta == 0){ // no difference
		h = 0;
	}else if (cmax == r){ // red is max
		h = ((g - b) / delta) % 6;
	}else if (cmax == g){
		h = (b - r) / delta + 2; // green is max
	}else{
		h = (r - g) / delta + 4; // blue is max
	}
	h = Math.round(h * 60);
	if (h < 0) h += 360;

	// calculate lightness
	let l = (cmax + cmin) / 2;

	// calculate saturation
	let s = delta == 0 ? 0 : delta / (1 - Math.abs(2 * l - 1));

	// make s and l percents
	return [h, Math.round(s*100), Math.round(l*100)];
}

function hsl2hex(h, s, l){
	let c = (1 - Math.abs(2 * l/100 - 1)) * s/100;
	let x = c * (1 - Math.abs((h / 60) % 2 - 1));
	let m = l/100 - c/2;
	let r, g, b;
	
	if (0 <= h && h < 60) {
		r = c; g = x; b = 0;
	} else if (60 <= h && h < 120) {
		r = x; g = c; b = 0;
	} else if (120 <= h && h < 180) {
		r = 0; g = c; b = x;
	} else if (180 <= h && h < 240) {
		r = 0; g = x; b = c;
	} else if (240 <= h && h < 300) {
		r = x; g = 0; b = c;
	} else if (300 <= h && h < 360) {
		r = c; g = 0; b = x;
	}

	r = Math.round((r + m) * 255);
	g = Math.round((g + m) * 255);
	b = Math.round((b + m) * 255);
	
	return `#${toHex(r)}${toHex(g)}${toHex(b)}`;
}

function toHex(d) {
	d = d.toString(16);
	if (d.length == 1) d = `0${d}`;
	return d.toUpperCase();
}

and now I can play with colors to my heart's content!

The way browser history is implemented, with the History interface, is useful for other things than site navigation. The same idea, basically an extended stack that allows going back and forward, is the same algorithm used for undo/redo, and command line history.

It would be nice to be able to do const h = new History() and h.pushState(someData) with arbitrary states, but the browser won't let you construct a new instance of History. It's only accessible from window.history.

So I re-defined History to allow this.

See the details on the github site.