A Pen By
Adobe Web Platform

` ````
<body onload="drawGradient()" onchange="drawGradient()">
<p>Midpoint: <input type="number" id="midPoint" min="5" max="95" value="50"></p>
<p>Color 1: <input type="color" id="c1" value="#ff0000"></p>
<p>Color 2: <input type="color" id="c2" value="#0000ff"></p>
<canvas id="c"></canvas>
<p id="formula"></p>
</body>
```

` ````
function getRgb(c){
c= c.toLowerCase();
if (/^[a-z]+$/.test(c)){
var colornames={
aqua:'#00ffff', black:'#000000', blue:'#0000ff', fuchsia:'#ff00ff',
gray:'#808080', green:'#008000', lime:'#00ff00', maroon:'#800000',
navy:'#000080', olive:'#808000', orange:'#ffa500', purple:'#800080',
red:'#ff0000', silver:'#c0c0c0', teal:'#008080', white:'#ffffff',
yellow:'#ffff00'
}
c= colornames[c];
}
if(/^#([a-f0-9]{3}){1,2}$/.test(c)){
if(c.length== 4){
c= '#'+[c[1], c[1], c[2], c[2], c[3], c[3]].join('');
}
c= '0x'+c.substring(1);
return [(c>>16)&255, (c>>8)&255, c&255];
}
else if(c.indexOf('rgb')== 0){
c= c.match(/\d+(\.\d+)?%?/g);
if(c){
for(var i= 0;i<3;i++){
if(c[i].indexOf('%')!= -1){
c[i]= Math.round(parseFloat(c[i])*2.55);
}
if(c[i]<0) c[i]= 0;
if(c[i]>255) c[i]= 255;
}
return c;
}
}
}
function drawGradient(){
var ctx = document.getElementById('c').getContext('2d');
var mid = document.getElementById('midPoint').valueAsNumber;
var c1 = getRgb(document.getElementById('c1').value);
var c2 = getRgb(document.getElementById('c2').value);
var exp = Math.log(.5)/Math.log(mid/100);
for(x = 0; x < 256; x++) {
var s = "rgb(";
s += Math.floor(c1[0] + Math.pow(x/255, exp)*(c2[0]-c1[0])) + ",";
s += Math.floor(c1[1] + Math.pow(x/255, exp)*(c2[1]-c1[1])) + ",";
s += Math.floor(c1[2] + Math.pow(x/255, exp)*(c2[2]-c1[2])) + ")";
ctx.fillStyle = s;
ctx.fillRect(x/256*ctx.canvas.width, 0, ctx.canvas.width, ctx.canvas.height);
}
var s = "gradient formula: c = c1 + (c2 - c1)^(log(.5)/log(" + mid + "/100)";
s += " = c1 + (c2 - c1)^" + exp;
$("#formula").text(s);
}
```

999px

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