to rotate image about its center in js as mouse moves code example
Example 1: transform matrix mousemove spin
var canvas = document.getElementById('canvas');
var ctx = canvas.getContext('2d');
class Circle {
constructor(options) {
this.cx = options.x;
this.cy = options.y;
this.radius = options.radius;
this.color = options.color;
this.angle = 0;
this.toAngle = this.angle;
this.binding();
}
binding() {
const self = this;
window.addEventListener('mousemove', (e) => {
self.update(e.clientX, e.clientY);
});
}
update(nx, ny) {
this.toAngle = Math.atan2(ny - this.cy, nx - this.cx);
}
render() {
ctx.clearRect(0,0,canvas.width,canvas.height);
ctx.save();
ctx.beginPath();
ctx.lineWidth = 1;
ctx.translate(this.cx, this.cy);
if (this.toAngle !== this.angle) {
ctx.rotate(this.toAngle - this.angle);
}
ctx.strokeStyle = this.color;
ctx.arc(0, 0, this.radius, 0, Math.PI * 2);
ctx.stroke();
ctx.closePath();
ctx.beginPath();
ctx.fillStyle = 'black';
ctx.fillRect(-this.radius / 4, -this.radius / 4, 20, 20);
ctx.closePath();
ctx.restore();
}
}
var rotatingCircle = new Circle({
x: 150,
y: 100,
radius: 40,
color: 'black'
});
function animate() {
rotatingCircle.render();
requestAnimationFrame(animate);
}
animate();
Example 2: transform matrix mousemove spin
ctx.beginPath();
ctx.lineWidth = 1;
ctx.translate(this.cx, this.cy); // translate to pivot
if (this.toAngle !== this.angle) {
ctx.rotate(this.toAngle - this.angle);
}
ctx.strokeStyle = this.color;
ctx.arc(0, 0, this.radius, 0, Math.PI * 2); // render at pivot
ctx.closePath(); // must come before stroke() btw.
ctx.stroke();
ctx.beginPath();
ctx.fillStyle = 'black';
ctx.fillRect(-this.radius / 4, -this.radius / 4, 20, 20); // render at pivot