Canvas: Difference between revisions

Revision as of 15:16, 25 September 2012

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

A example for color cycling with the canvas element [[1]]

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" width="300" height="300"> function draw(){

 c = document.getElementById("c1")
 //console.log("c is",c)
 p = c.getContext("2d")
 x = 10
 while (x<300) {
   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

@@ Line 48: / Line 48: @@
 Here's the output:
-<canvas width="300" height="300">
+<canvas id="c1" width="300" height="300">
 function draw(){
-   c = document.getElementById("canvas")
+   c = document.getElementById("c1")
    //console.log("c is",c)
    p = c.getContext("2d")
@@ Line 64: / Line 64: @@
 It redefines the "x" value to the begin of the line and adds 40px to "y".
-<canvas width="300" height="300" showsrc="true">
+<canvas id="c2" width="300" height="300" showsrc="true">
 	function draw(){
-		c = document.getElementById("canvas");
+		c = document.getElementById("c2");
-		console.log("c is ", c);
 		p = c.getContext("2d");
 		hands = 1;