Canvas: Difference between revisions

Revision as of 15:29, 25 September 2012

The canvas tag was introduced by Apple and has been standardized to become part of HTML5.

An example for color cycling with the canvas element

Get the canvas tag:

c=document.getElementById("c")

Get the "context" (like a paper):

p=c.getContext("2d");

Draw something!

p.fillRect(0, 0, 100, 100);

Examples

Here is a complete HTML page with a working canvas:

<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8" />
<script>
function draw(){
  c = document.getElementById("canvas")
  //console.log("c is",c)
  p = c.getContext("2d")
  x = 10
  while (x<300) {
    p.strokeRect(x,100,20,40)
    x+=60
  }
}
</script>
</head>
<body onload="draw()">
<h1>Hello canvas</h1>
<canvas id="canvas" width="640" height="640" style="border: 3px dotted red"></canvas>
</body>
</html>

Here's the output:

<canvas id="c1"> function draw(){

 c = document.getElementById("c1")
 //console.log("c is",c)
 p = c.getContext("2d")
 x = 10
 while (x<250) {
   p.strokeRect(x,100,20,40)
   x+=60
 }

} </canvas>

Variation: When the loop reaches the end of page it breaks the line. It redefines the "x" value to the begin of the line and adds 40px to "y".

<canvas id="c2" width="300" height="300" showsrc="true"> function draw() {

   c = document.getElementById("c2");
   p = c.getContext("2d");
   hands = 1;
   x = 20;
   y = 200;
   while (hands < 100) {
       //console.log(hands);
       p.strokeRect(x,y,20,20);
       x = x + 50;
       hands++;
       if (x > 600) {
           x = 20;
           y = y + 40;
       }
   }

} </canvas>

Tutorials & Reference