building a color wheel in html5
Question
I am just learning some details about html5 canvas, and in the progress, I am trying to build a simple color wheel by wedges (build a 1 degree wedge at a time and add it up to 360 degree). However, I am getting some weird marks on the gradient as shown in the following image:
.
Here is the fiddle that produced the colorwheel: http://jsfiddle.net/53JBM/
In particular, this is the JS code:
var canvas = document.getElementById("picker");
var context = canvas.getContext("2d");
var x = canvas.width / 2;
var y = canvas.height / 2;
var radius = 100;
var counterClockwise = false;
for(var angle=0; angle<=360; angle+=1){
var startAngle = (angle-1)*Math.PI/180;
var endAngle = angle * Math.PI/180;
context.beginPath();
context.moveTo(x, y);
context.arc(x, y, radius, startAngle, endAngle, counterClockwise);
context.closePath();
context.fillStyle = 'hsl('+angle+', 100%, 50%)';
context.fill();
}
If anyone can point out what I am doing wrong or if there is a better way to accomplish what I am attempting to do it would be much appreciated :)
3 answers
solution1
8 ACCPTED 2013-08-16 04:36:18
这对你来说够了，请检查
var startAngle = (angle-2)*Math.PI/180;
solution2
5 2015-04-04 22:21:12
Try this it looks great. Thanks by the way this is exactly what I was trying to make.
var canvas = document.getElementById("picker"); var context = canvas.getContext("2d"); var x = canvas.width / 2; var y = canvas.height / 2; var radius = 100; var counterClockwise = false; for(var angle=0; angle<=360; angle+=1){ var startAngle = (angle-2)*Math.PI/180; var endAngle = angle * Math.PI/180; context.beginPath(); context.moveTo(x, y); context.arc(x, y, radius, startAngle, endAngle, counterClockwise); context.closePath(); var gradient = context.createRadialGradient(x, y, 0, x, y, radius); gradient.addColorStop(0,'hsl('+angle+', 10%, 100%)'); gradient.addColorStop(1,'hsl('+angle+', 100%, 50%)'); context.fillStyle = gradient; context.fill(); }
<body> <canvas id="picker"></canvas> </body>
solution3
0 2018-07-21 11:36:50
Similar approach, just for the color
var canvas = document.getElementById("picker"); var context = canvas.getContext("2d"); var x = canvas.width / 2; var y = canvas.height / 2; var radius = 50; var thickness = 0.6; for(var angle=0; angle<=360; angle+=1){ var startAngle = (angle-2)*Math.PI/180; var endAngle = angle * Math.PI/180; context.beginPath(); context.arc(x, y, (1-thickness/2)*radius, startAngle, endAngle, false); context.lineWidth = thickness*radius; context.strokeStyle = 'hsl('+angle+', 100%, 50%)'; context.stroke(); }
<body> <canvas id="picker"></canvas> </body>
Edit: full project here: https://github.com/dersimn/jquery-colorwheel
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