HTML5 Canvas Line

Last update on August 19 2022 21:50:55 (UTC/GMT +8 hours)

Draw Lines

To draw a line using HTML5 Canvas is simple, just like draw a line on a paper, define a path, and then fill the path. See the following steps :

Resets the current path using beginPath() method.
Let move the drawing cursor to start point to create a new subpath using moveTo(x,y) method.
Now use lineTo(x, y) method, which adds a new point and connects this point to the starting point by using a straight line.
Both the above methods accept x and y parameters which tell it exactly where you want to draw the line.
Finally use stroke() method to make the line visible.

Pictorial Presentation:

html5 canvas pictorial line - w3resource

Example : Draw a simple Line

The following code will draw a simple line from (10,45) to (180,40).

Output :

<!DOCTYPE html>
<html>
<head>
<meta charset=utf-8 />
<title>Draw a line</title>
</head>
<body>
<canvas id="DemoCanvas" width="500" height="200"></canvas>  
<script>  
var canvas = document.getElementById('DemoCanvas');
//Always check for properties and methods, to make sure your code doesn't break in other browsers.
if (canvas.getContext) 
 {
  var context = canvas.getContext('2d');
  // Reset the current path
  context.beginPath(); 
  // Staring point (10,45)
   context.moveTo(10,45);
  // End point (180,47)
  context.lineTo(180,47);
  // Make the line visible
  context.stroke();
   }
</script> 
</body>
</html>

Example : Draw horizontal and vertical lines

The following code example uses the moveTo and lineTo methods to incrementally draw horizontal and vertical lines across the canvas.

Output:

HTML5 Canvas : horizontal and vertical lines

<!DOCTYPE html>
<html>
<head>
<meta charset=utf-8 />
<title>Draw a line</title>
</head>
<body>
<canvas id="DemoCanvas" width="400" height="400"></canvas>  
<script>  
var canvas = document.getElementById('DemoCanvas');
if (canvas.getContext) 
 {
  var ctx = canvas.getContext("2d");
     for (i = 10; i < 200; i += 20) 
	     {
		   ctx.moveTo(0, i);
		   ctx.lineTo(canvas.width, i);
		   ctx.stroke();
		  }
     for (i = 10; i <400; i += 20) 
	     {
		   ctx.moveTo(i, 0);
		   ctx.lineTo(i,canvas.width/2);
		   ctx.stroke();
		  }
  } 
</script>  
</body>
</html>

Line width

The lineWidth property gives the width (in pixels) of lines. The property value is a positive number (default value 1). On setting, zero, negative, and NaN values must be ignored, leaving the value unchanged. The following example draws a series of lines by using increasing values (1 to 12) for the lineWidth property.

Output:

<!DOCTYPE html>
<html>
<head>
<meta charset=utf-8 />
<title>Draw lines of various width</title>
</head>
<body>
<canvas id="DemoCanvas" width="400" height="400"></canvas>  
<script>
var canvas = document.getElementById('DemoCanvas');
if (canvas.getContext) 
{
 var context = canvas.getContext("2d");
 context.beginPath();
  context.moveTo(50, 10);
  context.lineTo(50, 200);
  context.lineWidth = 5;
  // set line color
  context.strokeStyle = 'red';
  context.stroke();
  context.beginPath();
  context.moveTo(100, 10);
  context.lineTo(100, 200);
  context.lineWidth = 5;
  // set line color
  context.strokeStyle = 'green';
  context.stroke();
  context.beginPath();
  context.moveTo(150, 10);
  context.lineTo(150, 200);
  context.lineWidth = 5;
  // set line color
  context.strokeStyle = '#2E1919';
  context.stroke();
  context.stroke();
  context.beginPath();
  context.moveTo(200, 10);
  context.lineTo(200, 200);
  context.lineWidth = 5;
  // set line color
  context.strokeStyle = '#3B4839';
  context.stroke();   
}
</script>  
</body>
</html>

Color Lines

To draw color lines you can use strokeStyle property, the default color is black. Syntax of the property is object.strokeStyle = color. Here is an example :

<!DOCTYPE html>
<html>
<head>
<meta charset=utf-8 />
<title>Color Lines</title>
</head>
<body>
<canvas id="DemoCanvas" width="400" height="400"></canvas>  
<script>
var canvas = document.getElementById('DemoCanvas');
 if (canvas.getContext) 
  {
    var context = canvas.getContext("2d");
	context.beginPath();
	context.moveTo(100, 10);
	context.lineTo(100, 200);
	context.lineWidth = 5;
	// set line color
	context.strokeStyle = '#808000';
	context.stroke();
  }
    </script>  
	</body>
	</html>

Line Cap

lineCap property is used to gets or sets the current line cap style. There are three cap styles :

butt : Default. A flat edge is put perpendicular to each end of the line with no cap added.
round : A semicircle or rounded end cap is added to each end of the line.
square : A square end cap is added to each end of the line.

Here is an example :

Output :

<!DOCTYPE html>
<html>
<head>
<meta charset=utf-8 />
<title>Line Cap</title>
</head>
<body>
<canvas id="DemoCanvas" width="400" height="400"></canvas>  
<script>
var canvas = document.getElementById('DemoCanvas');
if (canvas.getContext) 
{
 var context = canvas.getContext("2d");
 // butt line cap (first line)
      context.beginPath();
      context.moveTo(20,20);
      context.lineTo(20,200);
      context.lineWidth = 25;
      context.strokeStyle = '#ff0000';
      context.lineCap = 'butt';
      context.stroke();

  // round line cap (second line)
      context.beginPath();
      context.moveTo(80,20);
      context.lineTo(80,200);
      context.lineWidth = 25;
      context.strokeStyle = '#ff0000';
      context.lineCap = 'round';
      context.stroke();

 // square line cap (third line)
      context.beginPath();
      context.moveTo(120,20);
      context.lineTo(120,200);
      context.lineWidth = 25;
      context.strokeStyle = '#ff0000';
      context.lineCap = 'square';
      context.stroke();
}
</script>  
</body>
</html>

Line Join

lineJoin property is used to get or set the type of corner that is created when two lines join. There are three values :

bevel : A filled triangle connects the two lines that are joined, creating a beveled corner.
round : Lines join with a rounded corner.
square : Default. Lines join with a smoothly mitered corner.

Here is an example :

Output :

<!DOCTYPE html>
 <html>
 <head>
 <meta charset=utf-8 />
 <title>Line Joining</title>
 </head>
 <body>
 <canvas id="DemoCanvas" width="400" height="400"></canvas>  
<script>
var canvas = document.getElementById('DemoCanvas');
if (canvas.getContext) 
{
   var ctx = canvas.getContext("2d");
   var lStart = 50;
   var lEnd = 200;
   var yStart = 20;
   ctx.beginPath();
   ctx.lineWidth = 25;
// Use a bevel corner.
   ctx.lineJoin = "bevel";
   ctx.moveTo(50, 20);
   ctx.lineTo(150, 20);
   ctx.lineTo(150, 120);
   ctx.stroke();
// Use a round corner.             
   ctx.beginPath();
   ctx.lineJoin = "round";
   ctx.moveTo(50, 140);
   ctx.lineTo(150, 140);
   ctx.lineTo(150, 260);
   ctx.stroke();
// Use a miter.      
   ctx.beginPath();
   ctx.lineJoin = "miter";
   ctx.moveTo(50, 280);
   ctx.lineTo(150, 280);
   ctx.lineTo(150, 400); 
   ctx.stroke();
 }
</script>
</body>
</html>

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