HTML5 Canvas - Drawing Lines


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Line Methods

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

Sr.No. Method 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>
      
      <style>
         #test {
            width: 100px;
            height:100px;
            margin: 0px auto;
         }
      </style>
      
      <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 id="test" onload="drawShape();">
      <canvas id="mycanvas"></canvas>
   </body>
   
</html>

The above example would draw following shape −

Line Properties

There are several properties which allow us to style lines.

Sr.No. Property 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>
      
      <style>
         #test {
            width: 100px;
            height:100px;
            margin: 0px auto;
         }
      </style>
      
      <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 id="test" onload="drawShape();">
      <canvas id="mycanvas"></canvas>
   </body>
</html>

The above example would draw following shape −


html5_canvas.htm

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