Draw arc will linear gradient html5 canvas

Yes, it's possible! There is a method in Javascript, named createLinearGradient which gets as source the canvas context and applies a gradient defined by sx, sy, dx, dy coordinates. The first two options defines the starting coordinates and last two the ending coordinates. 

var gradient = context.createLinearGradient(sx, sy, dx, dy);

After invoking this method you can apply gradient colors to your canvas by calling the colorStop method:

gradient.addColorStop(0,   '#f00'); // red
gradient.addColorStop(0.5, '#ff0'); // yellow
gradient.addColorStop(1,   '#00f'); // blue

These are the basic ingredients for implementing a gradient on a canvas. The next step would be to calculate the circular color gradient positions if you need a circular gradient. This can be satisfied by the following formula:

var applyAngle = function (point, angle, distance) {
    return {
          x : point.x + (Math.cos(angle) * distance),
          y : point.y + (Math.sin(angle) * distance)
    };
};

Then plugin the resulted x and y position into the createLinearGradient method, which would create a nice looking circular gradient. Of course you need to use the arc method to make it circular.


I couldn't see the example that the OP posted (broken link?), but I had a very similar question and none of the answers here helped me.

So, this is what I wanted to do:

And this is how I did it:

var center = { "x": 115, "y": 115 };
var radius = 100;
var quadrants = [
	{
    	"angleStart": Math.PI * -0.5,
        "angleEnd": 0,
    	"x1": center.x,
        "y1": center.y - radius,
        "x2": center.x + radius,
        "y2": center.y,
        "colorStops": [
        	{ "stop": 0, "color": "blue" },
            { "stop": 1, "color": "green" }
        ]
    },
	{
    	"angleStart": 0,
        "angleEnd": Math.PI * 0.5,
    	"x1": center.x + radius,
        "y1": center.y,
        "x2": center.x,
        "y2": center.y + radius,
        "colorStops": [
        	{ "stop": 0, "color": "green" },
            { "stop": 1, "color": "yellow" }
        ]
    },
	{
    	"angleStart": Math.PI * 0.5,
        "angleEnd": Math.PI,
    	"x1": center.x,
        "y1": center.y + radius,
        "x2": center.x - radius,
        "y2": center.y,
        "colorStops": [
        	{ "stop": 0, "color": "yellow" },
            { "stop": 1, "color": "red" }
        ]
    },
	{
    	"angleStart": Math.PI,
        "angleEnd": Math.PI * 1.5,
    	"x1": center.x - radius,
        "y1": center.y,
        "x2": center.x,
        "y2": center.y - radius,
        "colorStops": [
        	{ "stop": 0, "color": "red" },
            { "stop": 1, "color": "black" }
        ]
    }    
];

var c = document.getElementById("myCanvas");
var ctx = c.getContext("2d");
// Draw arc quadrants.
for (var i = 0; i < quadrants.length; ++i) {
  var quad = quadrants[i];
  var grad = ctx.createLinearGradient(quad.x1, quad.y1, quad.x2, quad.y2);
  // Color stops.
  for (var j = 0; j < quad.colorStops.length; ++j) {
    var cs = quad.colorStops[j]; 
    grad.addColorStop(cs.stop, cs.color);
  }
  // Draw arc.
  ctx.beginPath();
  ctx.arc(center.x, center.y, radius, quad.angleStart, quad.angleEnd);
  ctx.strokeStyle = grad;
  ctx.lineWidth = 30;
  ctx.stroke();
}
<!DOCTYPE html>
<html>
<body>

<canvas id="myCanvas" width="230" height="230" style="border:1px solid #d3d3d3;">
Your browser does not support the HTML5 canvas tag.</canvas>
<p><strong>Note:</strong> The canvas tag is not supported in Internet 
Explorer 8 and earlier versions.</p>

</body>
</html>

And below is my draft idea before implementing it:

Linear gradient distribution on arc:

               ***********
          ***       |       ***
       **           |           **
     **             |             **
    *     _         |               *
  **       /|       |      \         **
 **       /         |      _\|        **
 *                  |                  *
*    4th Quadrant   |   1st Quadrant    *
*                   |                   *
*-------------------|-------------------*
*                   |                   *
*    3rd Quadrant   |   2nd Quadrant    *
 *          _       |                  *
 **       |\        |         /       **
  **        \       |       |/_      **
    *               |               *
     **             |             **
       **           |           **
          ***       |       ***
               ***********

Tags:

Html

Canvas

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