HTML5 Canvas - Drawing Lines


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Line Methods

There are following methods required to draw lines on the canvas:

SNMethod and Description
1

beginPath()

This method resets the current path.

2

moveTo(x, y)

This method creates a new subpath with the given point.

3

closePath()

This method marks the current subpath as closed, and starts a new subpath with a point the same as the start and end of the newly closed subpath.

4

fill()

This method fills the subpaths with the current fill style.

5

stroke()

This method strokes the subpaths with the current stroke style.

6

lineTo(x, y)

This method adds the given point to the current subpath, connected to the previous one by a straight line.

Example

Following is a simple example which makes use of above mentioned methods to draw a triangle.

<!DOCTYPE HTML>
<html>
<head>
<script type="text/javascript">
function drawShape(){
  // get the canvas element using the DOM
  var canvas = document.getElementById('mycanvas');
 
  // Make sure we don't execute when canvas isn't supported
  if (canvas.getContext){
 
    // use getContext to use the canvas for drawing
    var ctx = canvas.getContext('2d');
 
    // Filled triangle
    ctx.beginPath();
    ctx.moveTo(25,25);
    ctx.lineTo(105,25);
    ctx.lineTo(25,105);
    ctx.fill();
    
    // Stroked triangle
    ctx.beginPath();
    ctx.moveTo(125,125);
    ctx.lineTo(125,45);
    ctx.lineTo(45,125);
    ctx.closePath();
    ctx.stroke();
 
  } else {
    alert('You need Safari or Firefox 1.5+ to see this demo.');
  }
}
</script>
</head>
<body onload="drawShape();">
   <canvas id="mycanvas"></canvas>
</body>
</html>

The above example would draw following shape:

Canvas Lines

To learn above concept - Do Online Practice using latest version of either Safari or Opera.

Line Properties:

There are several properties which allow us to style lines.

SNProperty and Description
1

lineWidth [ = value ]

This property returns the current line width and can be set, to change the line width.

2

lineCap [ = value ]

This property returns the current line cap style and can be set, to change the line cap style. The possible line cap styles are butt, round, and square

3

lineJoin [ = value ]

This property returns the current line join style and can be set, to change the line join style. The possible line join styles are bevel, round, and miter.

4

miterLimit [ = value ]

This property returns the current miter limit ratio and can be set, to change the miter limit ratio.

Example

Following is a simple example which makes use of lineWidth property to draw lines of different width.

<!DOCTYPE HTML>
<html>
<head>
<script type="text/javascript">
function drawShape(){
  // get the canvas element using the DOM
  var canvas = document.getElementById('mycanvas');
 
  // Make sure we don't execute when canvas isn't supported
  if (canvas.getContext){
 
    // use getContext to use the canvas for drawing
    var ctx = canvas.getContext('2d');
 
    for (i=0;i<10;i++){
       ctx.lineWidth = 1+i;
       ctx.beginPath();
       ctx.moveTo(5+i*14,5);
       ctx.lineTo(5+i*14,140);
       ctx.stroke();
    }
  } else {
    alert('You need Safari or Firefox 1.5+ to see this demo.');
  }
}
</script>
</head>
<body onload="drawShape();">
   <canvas id="mycanvas"></canvas>
</body>
</html>

The above example would draw following shape:

Canvas Line Width

To learn above concept - Do Online Practice using latest version of either Safari or Opera.


html5_canvas.htm