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              <main class="main">
  <canvas id="canvas"></canvas>
</main>
            
          
!
            
              (function(){
	let canvas;
	let context;
	let width = 320;
	let height = 320;
	let mouse = {
		position: {
			x: 100,
			y: 100
		},
		offset: {
			x: 100,
			y: 100
		}
	};
	let particles = [];
	const NUM_OF_PARTICLES = 10;
	let requestAnimationFrame = 
		window.requestAnimationFrame ||
     window.mozRequestAnimationFrame ||
        window.webkitRequestAnimationFrame ||
     window.msRequestAnimationFrame;
    window.requestAnimationFrame = requestAnimationFrame;

	document.addEventListener("DOMContentLoaded", ()=>{
		canvas = document.getElementById("canvas");
		canvas.width = width;
		canvas.height = height;
		context = canvas.getContext("2d");
		context.fillStyle = "rgb(0, 0, 0)";
		context.fillRect(0, 0, width, height);

		canvas.addEventListener("mousemove", (e)=>{
			mouse_offset_move(e)
		});

		set_up_particles();

		draw();
	});

	function set_up_particles(){
		for(let i = 0; i < NUM_OF_PARTICLES; i += 1){
			let stalker_circle = {
				position: {
					x: 100,
					y: 100
				},
				angle: 0,
				radius: 3,
				speed: 0.05+Math.random()*0.05,
				orbit: 1 + Math.random()* 3,
				color: "rgb(" + Math.floor(Math.random()*255) + "," + Math.floor(Math.random()*255) + "," + Math.floor(Math.random()*255) + ")"
			};
			particles[i] = stalker_circle;
		}
	}

	function draw(){
		mouse_position_move()

		draw_canvas_layer();

		draw_mouse_stalkers();

		requestAnimationFrame(draw);
	}

	function mouse_position_move(){
		let sx = mouse.offset.x;
		let sy = mouse.offset.y;
		if(mouse.position.x !== sx &&
			mouse.position.y !== sy){
			mouse.position.x = sx;
			mouse.position.y = sy;
		}
	}

	function mouse_offset_move(e){
		mouse.offset.x = e.x;
		mouse.offset.y = e.y;

		return {
			x: e.x,
			y: e.y
		}
	}

	function draw_canvas_layer(){
		context.fillStyle = "rgba(0, 0, 0, .1)";
		context.fillRect(0, 0, width, height);
	}

	function draw_mouse_stalkers(){
		for(let i = 0; i < NUM_OF_PARTICLES; i += 1){
			let particle = particles[i];
			// 軌道上の(x,y)を作成
			particle.angle += particle.speed;

			let orbit_x = Math.cos(i + particle.angle) * particle.orbit;
			let orbit_y = Math.sin(i + particle.angle) * particle.orbit;
				
			// マウスの座標に向けて移動し、移動した点を中心とし軌道上に座標を打つ
			particle.position.x += (mouse.position.x - particle.position.x) * particle.speed + orbit_x;
			particle.position.y += (mouse.position.y - particle.position.y) * particle.speed + orbit_y;

			context.beginPath();
			context.arc(particle.position.x, particle.position.y, particle.radius, 0, Math.PI*2);
			context.fillStyle = particle.color;
			context.fill();

		}
	}
}());
            
          
!
999px
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