Create a rainbow radial gradient in JavaScript

Description

The following code shows how to create a rainbow radial gradient.

Example


<!DOCTYPE HTML>
<html>
<head>
<script>
function drawTriangle(context, x, y, triangleWidth, triangleHeight, fillStyle){
context.beginPath();<!--   www. j a  v  a  2 s  .  co m-->
context.moveTo(x, y);
context.lineTo(x + triangleWidth / 2, y + triangleHeight);
context.lineTo(x - triangleWidth / 2, y + triangleHeight);
context.closePath();
context.fillStyle = fillStyle;
context.fill();
}

window.onload = function(){
var canvas = document.getElementById("myCanvas");
var context = canvas.getContext("2d");

var grd;
var triangleWidth = 150;
var triangleHeight = 150;
var triangleY = canvas.height / 2 - triangleWidth / 2;

// radial gradient fill (second from right)
var centerX = 300;

var centerY = 100;

grd = context.createRadialGradient(centerX, centerY, 10, centerX, centerY, 100);
grd.addColorStop(0, "red");
grd.addColorStop(0.17, "orange");
grd.addColorStop(0.33, "yellow");
grd.addColorStop(0.5, "green");
grd.addColorStop(0.666, "blue");
grd.addColorStop(1, "violet");
drawTriangle(context, canvas.width / 2, triangleY, triangleWidth, triangleHeight, grd);

};
</script>
</head>
<body>
<canvas id="myCanvas" width="600" height="250" style="border:1px solid black;">
</canvas>
</body>
</html>

Click to view the demo

The code above generates the following result.

Create a rainbow radial gradient in JavaScript

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