Canvas波浪花环的示例代码

/* init() */
 function init(){
  wrapper = document.querySelector('#wrapper');
  canvas = createCanvas('canvas', width, height);
  wrapper.appendChild(canvas);
  ctx = canvas.getContext('2d');
  setupEvents();
  resizeCanvas();

/* Define new PlanetarySystem and set values */
  let system1 = new PlanetarySystem('pSys1');
  systems.push(system1);
  system1.x = width * .5;
  system1.y = height * .5;
  system1.addBody({id:'sun', diameter:5, degrees:0, speed:0, colour:'#FDFE1D', orbitalRadius:0, parentBody:null});
  for(let loop=30, i=0; i<loop; i+=1){
   system1.addBody({ id:    'ball'+i,
        diameter:  5,
        degrees:  0,
        speed:   2 + (loop * 0.15) - (i* 0.2),
        colour:   '#FDFE1D',
        orbitalRadius: 7*(i+1),
        parentBody:  'sun'});
  }
 }
 
/* Methods */
 function createCanvas(id, w, h){
  let tCanvas = document.createElement('canvas');
  tCanvas.width = w;
  tCanvas.height = h;
  tCanvas.id = id;
  return tCanvas;
 }

function setupEvents(){
  window.onresize = resizeCanvas;
 }
 function resizeCanvas(){
  let rect = wrapper.getBoundingClientRect();
  width = window.innerWidth;
  height = window.innerHeight - rect.top -2;
  canvas.width = width;
  canvas.height = height;
  for(let i=0; i<systems.length; i++){
   systems[i].x = width * .5;
   systems[i].y = height * .5;
  }
 }

function update(){
  for(let loop=systems.length, i=0; i<loop; i++){
   systems[i].update();
  }
 }

function draw(){
  let system;
  let prev = null;
  for(let i=0; i<systems.length; i++){
   system = systems[i];
   let planetaryBody;
   for(let loop=system.numBodies, j=1; j<loop; j+=1) {
    planetaryBody = system.allBodies[j];
    ctx.beginPath();
    ctx.arc(planetaryBody.x, planetaryBody.y, planetaryBody.diameter, 0, Tau, false);
    ctx.fillStyle = planetaryBody.colour;
    ctx.fill();
    if(j>1){
     ctx.strokeStyle = planetaryBody.colour;
     ctx.lineWidth = 2;
     ctx.beginPath();
     ctx.moveTo(planetaryBody.x, planetaryBody.y);
     ctx.lineTo(prev.x, prev.y);
     ctx.stroke();
    }
    prev = {x:planetaryBody.x, y:planetaryBody.y};
   }
  }
 }

function animate(){
  ctx.fillStyle = 'rgba(0,0,0, .05)';
  ctx.fillRect(0, 0, width, height);
  update();
  draw();
  requestAnimationFrame(animate);
 }
 init();
 animate();
}());
</script>
</html>

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