Rotate an image around its center in canvas

Question

I'm trying to do my first image animation on canvas. I want the image to rotate but something is not correct in my code. Any ideas? This is all in a jquery document ready:

var canvas = document.getElementById('logobg1');  
    var ctx = canvas.getContext('2d');

    var img = new Image();   // Create new Image object
    img.src = 'images/containerbg.png'; // Set source path // set img src

    img.onload = function(){ // when image loads
        ctx.drawImage(img,0,0);
        setInterval(function() {
            ctx.save();
            ctx.clearRect(-ctx.canvas.width/2, -ctx.canvas.height/2, ctx.canvas.width, ctx.canvas.height);
            ctx.drawImage(img,0,0);
            ctx.translate(ctx.canvas.width/2, ctx.canvas.height/2); // set canvas context to center
            ctx.rotate(Math.PI / 180 * 0.5); // 1/2 a degree
            ctx.restore();
        }, 16);
    }

Solution 1

Based in the accepted answer, this example, allows you to use a fixed canvas size (and not in relation to the image size):

 $(function() {
 
        var canvas = document.getElementById('logobg1');
        var ctx = canvas.getContext('2d');
        var img = new Image();
    
        var ang = 0; //angle
        var fps = 1000 / 25; //number of frames per sec
        img.onload = function () { //on image load do the following stuff
            canvas.width = 500; //Any width
            canvas.height = 500; //Any height
            var cache = this; //cache the local copy of image element for future reference
            var iw = cache.width;
            var ih = cache.height;
            setInterval(function () {
                ctx.save(); //saves the state of canvas
                ctx.clearRect(0, 0, canvas.width, canvas.height); //clear the canvas
                ctx.translate(canvas.width/2, canvas.height/2); //let's translate
                ctx.rotate(Math.PI / 180 * (ang += 5)); //increment the angle and rotate the image 
                ctx.translate(-(canvas.width/2), -(canvas.height/2)); //let's translate
                ctx.drawImage(img, canvas.width/2 - iw/2, canvas.height/2 - ih/2, iw, ih); //draw the image ;)
                ctx.restore(); //restore the state of canvas
            }, fps);
        };
        
        img.src = 'https://lh4.ggpht.com/wKrDLLmmxjfRG2-E-k5L5BUuHWpCOe4lWRF7oVs1Gzdn5e5yvr8fj-ORTlBF43U47yI=w300'; //img
 
 })
 

<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.2.1/jquery.min.js"></script>
<canvas id="logobg1" > test canvas <canvas>

Working example: jsbin.com/suwovibove/

Note: try removing ctx.save and ctx.restore for a cool spin.

Solution 2

Based on the comments above, but a bit more simple and in vanilla. This one worked for me perfectly. Of course you should use clearRect in order to erase the canvas on each rendering.

var canvas = document.querySelector('#my-canvas');
var ctx = canvas.getContext('2d')
var ang = 0

function rotateAndRenderImg() {
    var img = document.querySelector('img')
    ctx.save()
    var pos = {x: desiredRenderPosX, y: desiredRenderPosY}
    ctx.translate(pos.x ,pos.y)    
    ctx.rotate(Math.PI / 180 * (ang += 5))
    ctx.drawImage(img, -img.width / 2, -img.height / 2, img.width, img.height)
    ctx.restore()
}

Comments

[Jeroen van Langen]

Thanks for the example, Just for clarification, I would change the name of the variable fps because it is an interval.