HTML5 Canvas Rotate Image
Solution 1:
You can use canvas’ context.translate & context.rotate to do rotate your image
Here’s a function to draw an image that is rotated by the specified degrees:
function drawRotated(degrees){
context.clearRect(0,0,canvas.width,canvas.height);
// save the unrotated context of the canvas so we can restore it later
// the alternative is to untranslate & unrotate after drawing
context.save();
// move to the center of the canvas
context.translate(canvas.width/2,canvas.height/2);
// rotate the canvas to the specified degrees
context.rotate(degrees*Math.PI/180);
// draw the image
// since the context is rotated, the image will be rotated also
context.drawImage(image,-image.width/2,-image.width/2);
// we’re done with the rotating so restore the unrotated context
context.restore();
}
Here is code and a Fiddle: http://jsfiddle.net/m1erickson/6ZsCz/
<!doctype html>
<html>
<head>
<link rel="stylesheet" type="text/css" media="all" href="css/reset.css" /> <!-- reset css -->
<script type="text/javascript" src="http://code.jquery.com/jquery.min.js"></script>
<style>
body{ background-color: ivory; }
canvas{border:1px solid red;}
</style>
<script>
$(function(){
var canvas=document.getElementById("canvas");
var ctx=canvas.getContext("2d");
var angleInDegrees=0;
var image=document.createElement("img");
image.onload=function(){
ctx.drawImage(image,canvas.width/2-image.width/2,canvas.height/2-image.width/2);
}
image.src="houseicon.png";
$("#clockwise").click(function(){
angleInDegrees+=30;
drawRotated(angleInDegrees);
});
$("#counterclockwise").click(function(){
angleInDegrees-=30;
drawRotated(angleInDegrees);
});
function drawRotated(degrees){
ctx.clearRect(0,0,canvas.width,canvas.height);
ctx.save();
ctx.translate(canvas.width/2,canvas.height/2);
ctx.rotate(degrees*Math.PI/180);
ctx.drawImage(image,-image.width/2,-image.width/2);
ctx.restore();
}
}); // end $(function(){});
</script>
</head>
<body>
<canvas id="canvas" width=300 height=300></canvas><br>
<button id="clockwise">Rotate right</button>
<button id="counterclockwise">Rotate left</button>
</body>
</html>
Solution 2:
Quickest 2D context image rotation method
A general purpose image rotation, position, and scale.
// no need to use save and restore between calls as it sets the transform rather
// than multiply it like ctx.rotate ctx.translate ctx.scale and ctx.transform
// Also combining the scale and origin into the one call makes it quicker
// x,y position of image center
// scale scale of image
// rotation in radians.
function drawImage(image, x, y, scale, rotation){
ctx.setTransform(scale, 0, 0, scale, x, y); // sets scale and origin
ctx.rotate(rotation);
ctx.drawImage(image, -image.width / 2, -image.height / 2);
}
If you wish to control the rotation point use the next function
// same as above but cx and cy are the location of the point of rotation
// in image pixel coordinates
function drawImageCenter(image, x, y, cx, cy, scale, rotation){
ctx.setTransform(scale, 0, 0, scale, x, y); // sets scale and origin
ctx.rotate(rotation);
ctx.drawImage(image, -cx, -cy);
}
To reset the 2D context transform
ctx.setTransform(1,0,0,1,0,0); // which is much quicker than save and restore
Thus to rotate image to the left (anti clockwise) 90 deg
drawImage(image, canvas.width / 2, canvas.height / 2, 1, - Math.PI / 2);
Thus to rotate image to the right (clockwise) 90 deg
drawImage(image, canvas.width / 2, canvas.height / 2, 1, Math.PI / 2);
Example draw 500 images translated rotated scaled
var image = new Image;
image.src = "https://i.stack.imgur.com/C7qq2.png?s=328&g=1";
var canvas = document.createElement("canvas");
var ctx = canvas.getContext("2d");
canvas.style.position = "absolute";
canvas.style.top = "0px";
canvas.style.left = "0px";
document.body.appendChild(canvas);
var w,h;
function resize(){ w = canvas.width = innerWidth; h = canvas.height = innerHeight;}
resize();
window.addEventListener("resize",resize);
function rand(min,max){return Math.random() * (max ?(max-min) : min) + (max ? min : 0) }
function DO(count,callback){ while (count--) { callback(count) } }
const sprites = [];
DO(500,()=>{
sprites.push({
x : rand(w), y : rand(h),
xr : 0, yr : 0, // actual position of sprite
r : rand(Math.PI * 2),
scale : rand(0.1,0.25),
dx : rand(-2,2), dy : rand(-2,2),
dr : rand(-0.2,0.2),
});
});
function drawImage(image, spr){
ctx.setTransform(spr.scale, 0, 0, spr.scale, spr.xr, spr.yr); // sets scales and origin
ctx.rotate(spr.r);
ctx.drawImage(image, -image.width / 2, -image.height / 2);
}
function update(){
var ihM,iwM;
ctx.setTransform(1,0,0,1,0,0);
ctx.clearRect(0,0,w,h);
if(image.complete){
var iw = image.width;
var ih = image.height;
for(var i = 0; i < sprites.length; i ++){
var spr = sprites[i];
spr.x += spr.dx;
spr.y += spr.dy;
spr.r += spr.dr;
iwM = iw * spr.scale * 2 + w;
ihM = ih * spr.scale * 2 + h;
spr.xr = ((spr.x % iwM) + iwM) % iwM - iw * spr.scale;
spr.yr = ((spr.y % ihM) + ihM) % ihM - ih * spr.scale;
drawImage(image,spr);
}
}
requestAnimationFrame(update);
}
requestAnimationFrame(update);