JS/HTML5游戏像素碰撞检测算法详解

<!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-像素检测算法</title>
 <style>
  #stage {
   border: 1px solid lightgray;
  }
 </style>
</head>
<body>
<h1>包围盒是否碰撞：<span class="hitTestBox">否</span></h1>
<h1>像素检测是否碰撞：<span class="hitTestPixel">否</span></h1>
<canvas id="stage"></canvas>
<img src="./images/penguin.png" alt="penguinImg" id="penguinImg" style="display:none" />
<img src="./images/giraffe.png" alt="giraffeImg" id="giraffeImg" style="display:none" />
</body>
<script>
 window.onload = function () {
  var stage = document.querySelector('#stage'),
   ctx = stage.getContext('2d');
  stage.width = 600;
  stage.height = 600;
  //创建后台canvas
  var bC = document.createElement("canvas");
  bC.width = stage.width;
  bC.height = stage.height;
  var backBuf = bC.getContext("2d");
  var penguin = document.querySelector('#penguinImg'),giraffe = document.querySelector('#giraffeImg');
  var penguinImg = {
   x:stage.width/2,
   y:stage.height/2,
   r:128,
   data:null
  },giraffeImg = {
   x:100,
   y:100,
   r:128,
   data:null
  };
  function drawImageBox(img,x,y,width,height){
   ctx.beginPath();
   ctx.rect(x,y,width,height);
   ctx.stroke();
   ctx.drawImage(img,x,y,width,height);
  }
  //缓存画布绘制方法
  function drawImageBC(img,x,y,width,height){
   backBuf.clearRect(0,0,stage.width,stage.height);
   backBuf.save();
   backBuf.drawImage(img,x,y,width,height);
   backBuf.restore();
  }
  //获取两个矩形相交区域
  function getInRect(x1,y1,x2,y2,x3,y3,x4,y4) {
   return [Math.max(x1,x3),Math.max(y1,y3),Math.min(x2,x4),Math.min(y2,y4)];
  }
  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 (penguinImg.x > 0) {
      penguinImg.x -= 2;
     }
     break;
    case 38:
     console.log("Top");
     if (penguinImg.y > 0) {
      penguinImg.y -= 2;
     }
     break;
    case 39:
     console.log("Right");
     if (penguinImg.x < stage.width) {
      penguinImg.x += 2;
     }
     break;
    case 40:
     console.log("Bottom");
     if (penguinImg.y < stage.height) {
      penguinImg.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;
   penguinImg.x = x;
   penguinImg.y = y;
  });
  function update() {
   ctx.clearRect(0, 0, 600, 600);
   drawImageBox(giraffe,giraffeImg.x,giraffeImg.y,giraffeImg.r,giraffeImg.r);
   drawImageBox(penguin,penguinImg.x,penguinImg.y,penguinImg.r,penguinImg.r);
   document.querySelector('.hitTestBox').innerHTML = "否";
   document.querySelector('.hitTestPixel').innerHTML = "否";
   var rect = getInRect(giraffeImg.x,giraffeImg.y,giraffeImg.x+giraffeImg.r,giraffeImg.y+giraffeImg.r,penguinImg.x,penguinImg.y,penguinImg.x+penguinImg.r,penguinImg.y+penguinImg.r)
   //如果没有相交则退出
   if(rect[0]>=rect[2]||rect[1]>=rect[3]) {
   } else{
    document.querySelector('.hitTestBox').innerHTML = "是";
    giraffeImg.data = null;
    penguinImg.data = null;
    //获取精灵在相交矩形像素数据
    drawImageBC(giraffe,giraffeImg.x,giraffeImg.y,giraffeImg.r,giraffeImg.r);
    giraffeImg.data = backBuf.getImageData(rect[0],rect[1],rect[2],rect[3]).data;
    drawImageBC(penguin,penguinImg.x,penguinImg.y,penguinImg.r,penguinImg.r);
    penguinImg.data = backBuf.getImageData(rect[0],rect[1],rect[2],rect[3]).data;
    for(var i=3;i<giraffeImg.data.length;i+=4)
    {
     if(giraffeImg.data[i]>0&&penguinImg.data[i]>0){
      document.querySelector('.hitTestPixel').innerHTML = "是";
     }
    }
   }
   requestAnimationFrame(update);
  }
  update();
 };
</script>
</html>