JS/HTML5游戏开发：矩形包围盒（AABB）碰撞检测算法详解

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

<!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-矩形</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;
    //栅格线条
    function drawGrid(context, color, stepx, stepy) {
      context.strokeStyle = color;
      context.lineWidth = 0.5;
      for (var i = stepx + 0.5; i < context.canvas.width; i += stepx) {
        context.beginPath();
        context.moveTo(i, 0);
        context.lineTo(i, context.canvas.height);
        context.stroke();
      }
      for (var i = stepy + 0.5; i < context.canvas.height; i += stepy) {
        context.beginPath();
        context.moveTo(0, i);
        context.lineTo(context.canvas.width, i);
        context.stroke();
      }
    }
    var rect = {
      x: stage.width / 2 - 20,
      y: stage.height / 2 - 20,
      r: 40,
      c: "red"
    }, rects = [];;
    rects.push(rect);
    for (var i = 0; i < 10; i++) {
      var trace = {
        x: 40 * i,
        y: 40 * i,
        r: 40,
        c: "blue"
      };
      rects.push(trace);
    }
    function createRect(x, y, r, c) {
      ctx.beginPath();
      ctx.fillStyle = c;
      ctx.rect(x, y, r, r);
      ctx.fill();
    }
    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 (rects[0].x > 0) {
            rects[0].x -= 2;
          }
          break;
        case 38:
          console.log("Top");
          if (rects[0].y > 0) {
            rects[0].y -= 2;
          }
          break;
        case 39:
          console.log("Right");
          if (rects[0].x < stage.width) {
            rects[0].x += 2;
          }
          break;
        case 40:
          console.log("Bottom");
          if (rects[0].y < stage.height) {
            rects[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;
      rects[0].x = x - rects[0].r/2;
      rects[0].y = y - rects[0].r/2;
    });
    function hitTest(source, target) {
      /* 源物体和目标物体都包含 x, y 以及 width, height */
      return !(
        ( ( source.y + source.r ) < ( target.y ) ) ||
        ( source.y > ( target.y + target.r ) ) ||
        ( ( source.x + source.r ) < target.x ) ||
        ( source.x > ( target.x + target.r ) )
      );
    }
    function update() {
      ctx.globalAlpha = 1;
      ctx.clearRect(0, 0, 400, 400);
      drawGrid(ctx, 'lightgray', 40, 40);
      document.querySelector('.hitTest').innerHTML = "否";
      for (var i = 1, len = rects.length; i < len; i++) {
        createRect(rects[i].x, rects[i].y, rects[i].r, rects[i].c);
        var flag = hitTest(rects[0], rects[i]);
        if (flag) {
          document.querySelector('.hitTest').innerHTML = "是";
          ctx.globalAlpha = 0.5;
        }
      }
      createRect(rects[0].x, rects[0].y, rects[0].r, rects[0].c);
      requestAnimationFrame(update);
    }
    update();
  };
</script>
</html>