Menu
Am trying to draw a star using canvas, but the code is not running. I want to understand: what are the steps to measure the Y and X coordinate? How to find them? to draw any shape?
<html>
<head>
<meta charset = "utf-8">
<title>Drawing Lines</title>
</head>
<body>
<canvas id = "drawLines" width = "400" height = "200"
style = "border: 1px solid Black;">
</canvas>
<script>
var canvas = document.getElementById("drawLines");
var context = canvas.getContext("2d")
canvas.beginPath();
canvas.moveTo(50,50);
canvas.lineTo(120,150);
canvas.lineTo(0,180);
canvas.lineTo(120,210);
canvas.lineTo(50,310);
canvas.lineTo(160,250);
canvas.lineTo(190,370);
canvas.lineTo(220,250);
canvas.lineTo(330,310);
canvas.lineTo(260,210);
canvas.lineTo(380,180);
canvas.closePath();
canvas.stroke();
</script>
</body>
</html>
963
The arc() method is used to create a circle in HTML5 with the canvas element. For a circle with arc() method, use the start angle as 0 and end angle to 2*Math. PI.
Most of the web browsers can display SVG just like they can display PNG, GIF, and JPG. To draw a polygon in HTML SVG, use the SVG <polygon> element. The <polygon> element creates a graphic containing at least three sides. For drawing a star in HTML5 SVG, you need to set the x and y coordinates properly for each corner.
A star is basically a regular polygon with alternating points on an inner and an outer radius.
Here's an example of a flexible function to draw a star shape.
You can set the position, #spikes and the inner & outer radius of the spikes:
Example code and a Demo: http://jsfiddle.net/m1erickson/8j6kdf4o/
<!doctype html>
<html>
<head>
<link rel="stylesheet" type="text/css" media="all" href="css/reset.css" /> <!-- reset css -->
<script type="text/javascript" src="http://code.jquery.com/jquery.min.js"></script>
<style>
body{ background-color: ivory; }
canvas{border:1px solid red;}
</style>
<script>
$(function(){
var canvas=document.getElementById("canvas");
var ctx=canvas.getContext("2d");
function drawStar(cx,cy,spikes,outerRadius,innerRadius){
var rot=Math.PI/2*3;
var x=cx;
var y=cy;
var step=Math.PI/spikes;
ctx.beginPath();
ctx.moveTo(cx,cy-outerRadius)
for(i=0;i<spikes;i++){
x=cx+Math.cos(rot)*outerRadius;
y=cy+Math.sin(rot)*outerRadius;
ctx.lineTo(x,y)
rot+=step
x=cx+Math.cos(rot)*innerRadius;
y=cy+Math.sin(rot)*innerRadius;
ctx.lineTo(x,y)
rot+=step
}
ctx.lineTo(cx,cy-outerRadius);
ctx.closePath();
ctx.lineWidth=5;
ctx.strokeStyle='blue';
ctx.stroke();
ctx.fillStyle='skyblue';
ctx.fill();
}
drawStar(100,100,5,30,15);
}); // end $(function(){});
</script>
</head>
<body>
<canvas id="canvas" width=300 height=300></canvas>
</body>
</html>
The function can be shorter with coordinate translate:
function strokeStar(x, y, r, n, inset) {
ctx.save();
ctx.beginPath();
ctx.translate(x, y);
ctx.moveTo(0,0-r);
for (var i = 0; i < n; i++) {
ctx.rotate(Math.PI / n);
ctx.lineTo(0, 0 - (r*inset));
ctx.rotate(Math.PI / n);
ctx.lineTo(0, 0 - r);
}
ctx.closePath();
ctx.fill();
ctx.restore();
}
If you love us? You can donate to us via Paypal or buy me a coffee so we can maintain and grow! Thank you!
Donate Us With
