JS/HTML5游戏碰撞检测：圆形包围盒算法详解

  function hitTest( source, target ) {
   /* 源物体和目标物体都包含 x, y 以及 width, height */
   return !(
    Math.pow((source.x - target.x),2) + Math.pow((source.y - target.y),2) > Math.pow((source.r + target.r),2)
   );
  }

<!DOCTYPE html>
<html lang="en">
<head>
 <meta name="viewport" content="width=device-width, initial-scale=1.0, maximum-scale=1.0, user-scalable=0">
 <meta charset="UTF-8">
 <title>盒包围碰撞算法-圆形</title>
 <style>
  #stage {
   border: 1px solid lightgray;
  }
 </style>
</head>
<body>
<h1>是否碰撞：<span class="hitTest">否</span></h1>
<canvas id="stage"></canvas>
</body>
<script>
 window.onload = function () {
  var stage = document.querySelector('#stage'),
   ctx = stage.getContext('2d');
  stage.width = 400;
  stage.height = 400;
  document.onkeydown = function (event) {
   var e = event || window.event || arguments.callee.caller.arguments[0];
   //根据地图数组碰撞将测
   switch (e.keyCode) {
    case 37:
     console.log("Left");
     if (balls[0].x > 0) {
      balls[0].x -= 2;
     }
     break;
    case 38:
     console.log("Top");
     if (balls[0].y > 0) {
      balls[0].y -= 2;
     }
     break;
    case 39:
     console.log("Right");
     if (balls[0].x < stage.width) {
      balls[0].x += 2;
     }
     break;
    case 40:
     console.log("Bottom");
     if (balls[0].y < stage.height) {
      balls[0].y += 2;
     }
     break;
    default:
     return false;
   }
  };
  stage.addEventListener('click', function (event) {
   var x = event.clientX - stage.getBoundingClientRect().left;
   var y = event.clientY - stage.getBoundingClientRect().top;
   balls[0].x = x - balls[0].r/2;
   balls[0].y = y - balls[0].r/2;
  });
  var player = {
   x: stage.width / 2 - 20,
   y: stage.height / 2 - 20,
   r: 40,
   c: "red"
  },balls = [];
  balls.push(player);
  for (var i = 0; i < 10; i++) {
   var ball = {
    x: 60 * i,
    y: 60 * i,
    r: 40,
    c: "blue"
   };
   balls.push(ball);
  }
  function createBall(x, y, r, c) {
   ctx.beginPath();
   ctx.fillStyle = c;
   ctx.arc(x, y, r, 0, Math.PI*2);
   ctx.fill();
  }
  function hitTest( source, target ) {
   /* 源物体和目标物体都包含 x, y 以及 width, height */
   return !(
    Math.pow((source.x - target.x),2) + Math.pow((source.y - target.y),2) > Math.pow((source.r + target.r),2)
   );
  }
  function update() {
   ctx.globalAlpha=1;
   ctx.clearRect(0, 0, 400, 400);
   document.querySelector('.hitTest').innerHTML = "否";
   for (var i = 1, len = balls.length; i < len; i++) {
    createBall(balls[i].x, balls[i].y, balls[i].r, balls[i].c);
    var flag = hitTest(balls[0],balls[i]);
    if(flag){
     document.querySelector('.hitTest').innerHTML = "是";
     ctx.globalAlpha=0.5;
    }
   }
   createBall(balls[0].x, balls[0].y, balls[0].r, balls[0].c);
   requestAnimationFrame(update);
  }
  update();
 };
</script>
</html>