How to draw polygons on an HTML5 canvas?

Question

I need to know how to draw polygons on a canvas. Without using jQuery or anything like that.

Answer 1

from http://www.scienceprimer.com/drawing-regular-polygons-javascript-canvas:

The following code will draw a hexagon. Change the number of sides to create different regular polygons.

var ctx = document.getElementById('hexagon').getContext('2d');

// hexagon
var numberOfSides = 6,
    size = 20,
    Xcenter = 25,
    Ycenter = 25;

ctx.beginPath();
ctx.moveTo (Xcenter +  size * Math.cos(0), Ycenter +  size *  Math.sin(0));          

for (var i = 1; i <= numberOfSides;i += 1) {
  ctx.lineTo (Xcenter + size * Math.cos(i * 2 * Math.PI / numberOfSides), Ycenter + size * Math.sin(i * 2 * Math.PI / numberOfSides));
}

ctx.strokeStyle = "#000000";
ctx.lineWidth = 1;
ctx.stroke();

#hexagon { border: thin dashed red; }

<canvas id="hexagon"></canvas>

Answer 2

Create a path with moveTo and lineTo (live demo):

var ctx = canvas.getContext('2d');
ctx.fillStyle = '#f00';
ctx.beginPath();
ctx.moveTo(0, 0);
ctx.lineTo(100,50);
ctx.lineTo(50, 100);
ctx.lineTo(0, 90);
ctx.closePath();
ctx.fill();

Answer 3

//create and fill polygon
CanvasRenderingContext2D.prototype.fillPolygon = function (pointsArray, fillColor,     strokeColor) {
    if (pointsArray.length <= 0) return;
    this.moveTo(pointsArray[0][0], pointsArray[0][1]);
    for (var i = 0; i < pointsArray.length; i++) {
        this.lineTo(pointsArray[i][0], pointsArray[i][1]);
    }
    if (strokeColor != null && strokeColor != undefined)
        this.strokeStyle = strokeColor;

    if (fillColor != null && fillColor != undefined) {
        this.fillStyle = fillColor;
        this.fill();
    }
}
//And you can use this method as 
var polygonPoints = [[10,100],[20,75],[50,100],[100,100],[10,100]];
context.fillPolygon(polygonPoints, '#F00','#000');

Answer 4

Here is a function that even supports clockwise/anticlockwise drawing do that you control fills with the non-zero winding rule.

Here is a full article on how it works and more.

// Defines a path for any regular polygon with the specified number of sides and radius, 
// centered on the provide x and y coordinates.
// optional parameters: startAngle and anticlockwise

function polygon(ctx, x, y, radius, sides, startAngle, anticlockwise) {
  if (sides < 3) return;
  var a = (Math.PI * 2)/sides;
  a = anticlockwise?-a:a;
  ctx.save();
  ctx.translate(x,y);
  ctx.rotate(startAngle);
  ctx.moveTo(radius,0);
  for (var i = 1; i < sides; i++) {
    ctx.lineTo(radius*Math.cos(a*i),radius*Math.sin(a*i));
  }
  ctx.closePath();
  ctx.restore();
}

// Example using the function.
// Define a path in the shape of a pentagon and then fill and stroke it.
context.beginPath();
polygon(context,125,125,100,5,-Math.PI/2);
context.fillStyle="rgba(227,11,93,0.75)";
context.fill();
context.stroke();

Answer 5

//poly [x,y, x,y, x,y.....];
var poly=[ 5,5, 100,50, 50,100, 10,90 ];
var canvas=document.getElementById("canvas")
var ctx = canvas.getContext('2d');
ctx.fillStyle = '#f00';

ctx.beginPath();
ctx.moveTo(poly[0], poly[1]);
for( item=2 ; item < poly.length-1 ; item+=2 ){ctx.lineTo( poly[item] , poly[item+1] )}

ctx.closePath();
ctx.fill();

Answer 6

You can use the lineTo() method same as: var objctx = canvas.getContext('2d');

        objctx.beginPath();
        objctx.moveTo(75, 50);
        objctx.lineTo(175, 50);
        objctx.lineTo(200, 75);
        objctx.lineTo(175, 100);
        objctx.lineTo(75, 100);
        objctx.lineTo(50, 75);
        objctx.closePath();
        objctx.fillStyle = "rgb(200,0,0)";
        objctx.fill();

if you not want to fill the polygon use the stroke() method in the place of fill()

You can also check the following: http://www.authorcode.com/draw-and-fill-a-polygon-and-triangle-in-html5/

thanks