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8.1 HTML Canvas
- The HTML element is used to draw graphics on a web page.
- This graphic is created with . It shows four elements: a red rectangle, a gradient rectangle, a multicolor rectangle, and multicolor text.
What is HTML Canvas?
- The HTML element is used to draw graphics, on the fly, via JavaScript.
- The element is only a container for graphics. You must use JavaScript to actually draw the graphics.
- Canvas has several methods for drawing paths, boxes, circles, text, and adding images.
Browser Support
The numbers in the table specify the first browser version that fully supports the element.
| Element |  |
 |
 |
 |
 |
|---|---|---|---|---|---|
| <canvas> | 4.0 | 9.0 | 2.0 | 3.1 | 9.0 |
Canvas Examples
A canvas is a rectangular area on an HTML page. By default, a canvas has no border and no content.
The markup looks like this:
<canvas id="myCanvas" width="200" height="100"></canvas>
Note: Always specify an attribute (to be referred to in a script), and a and attribute to define the size of the canvas. To add a border, use the attribute.
Here is an example of a basic, empty canvas:
Example 1: HTML empty canvas
<canvas id="myCanvas" width="200" height="100" style="border:1px solid #000000;"> </canvas>
Add a JavaScript
After creating the rectangular canvas area, you must add a JavaScript to do the drawing.
Here are some examples:
Draw a line
Example 2: Canvas with a line
<script>
var c = document.getElementById("myCanvas");
var ctx = c.getContext("2d");
ctx.moveTo(0, 0);
ctx.lineTo(200, 100);
ctx.stroke();
</script>
Draw a Circle
Example 3: Canvas with a circle
<script>
var c = document.getElementById("myCanvas");
var ctx = c.getContext("2d");
ctx.beginPath();
ctx.arc(95, 50, 40, 0, 2 * Math.PI);
ctx.stroke();
</script>
Draw Text
Example 4: Canvas with text part 1
<script>
var c = document.getElementById("myCanvas");
var ctx = c.getContext("2d");
ctx.font = "30px Arial";
ctx.fillText("Hello World", 10, 50);
</script>
Stroke Text
Example 5: Canvas with text part 2
<script>
var c = document.getElementById("myCanvas");
var ctx = c.getContext("2d");
ctx.font = "30px Arial";
ctx.strokeText("Hello World", 10, 50);
</script>
Draw Linear Gradient
Example 6: Canvas with gradient rectangle
<script>
var c = document.getElementById("myCanvas");
var ctx = c.getContext("2d");
// Create gradient
var grd = ctx.createLinearGradient(0, 0, 200, 0);
grd.addColorStop(0, "red");
grd.addColorStop(1, "white");
// Fill with gradient
ctx.fillStyle = grd;
ctx.fillRect(10, 10, 150, 80);
</script>
Draw Circular Gradient
Example 7: Canvas with radial gradient rectangle
<script>
var c = document.getElementById("myCanvas");
var ctx = c.getContext("2d");
// Create gradient
var grd = ctx.createRadialGradient(75, 50, 5, 90, 60, 100);
grd.addColorStop(0, "red");
grd.addColorStop(1, "white");
// Fill with gradient
ctx.fillStyle = grd;
ctx.fillRect(10, 10, 150, 80);
</script>
Draw an Image
Image to use:
Example 8: Canvas with an image
<script>
var c = document.getElementById("myCanvas");
var ctx = c.getContext("2d");
var img = document.getElementById("scream");
ctx.drawImage(img, 10, 10);
</script>
HTML Canvas Tutorial
To learn more about , please read the HTML Canvas Tutorial.