Native js combined with html5 to create a simple jumping ball for the little flying dragon

Native js combined with html5 to create a simple jumping ball for the little flying dragon_javascript skills

WBOY

Release： 2016-05-16 16:07:10

Original

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Demo address: http://runjs.cn/detail/yjpvqhal

html code

<html>
  <head>
    <meta charset="utf-8"/>
    <title>小飞龙的跳球</title>
  </head>
  <body onload="init()">
    <canvas id="game" width="400" height="400" style="border:1px solid #c3c3c3">
      你的游览器不支持html5的画布元素，请升级到IE9+或使用firefox、chrome这类高级的智能游览器！
    </canvas>
    <script>
      var canvas = document.getElementById('game');
      var ctx = canvas.getContext('2d');
      var grad;
      //盒子的起始位置和大小以及球的半径
      var box = {x:20,y:20,w:350,h:350,r:20};
      //球的中心位置和偏移位置
      var inbox = {//box内的限制范围
          bx:(box.w+box.x-box.r),
          by:(box.h+box.y-box.r),
          ix:box.x+(box.r*2),
          iy:box.y+(box.r*2)
        };
      //球的初始位置和变化位置  
      var ball = {x:50,y:50,vx:4,vy:8};
      var img = new Image();
      img.src = 'images/qiuqiu.png';
      var hue = [[255,0,0],[255,255,0],[0,255,0],[0,255,255],[0,0,255],[255,0,0]];
      function init(){
        grad = ctx.createLinearGradient(box.x,box.y,box.w,box.h);
        for(var i=0;i<hue.length;i++){
          var color = 'rgb('+hue[i][0]+','+hue[i][1]+','+hue[i][2]+')';
          grad.addColorStop(i/hue.length,color);
        }
        ctx.lineWidth = box.r;
        ctx.fillStyle = 'rgb(200,0,50)';
        ctx.fillStyle = grad;
        moveBall();
        setInterval(moveBall,50);
      }  
      //碰撞检测并重新确定球的位置
      function moveBallEndCheck(){
        var nx = ball.x + ball.vx;
        var ny = ball.y + ball.vy;
        if(nx > inbox.bx){//当前x大于上边框边界
          ball.vx = -ball.vx;//球的变化x坐标当前当前变化x坐标的负数
          nx = inbox.bx;//当前位置为上边框的位置
        }
        if(nx < inbox.ix){//当前位置小于下边框
          nx = inbox.ix;//当前位置为下边框的x
          ball.vx = -ball.vx;//球的变化x坐标翻转取负
        }
        if(ny > inbox.by){
          ny = inbox.by;
          ball.vy = -ball.vy;
        }
        if(ny < inbox.iy){
          ny = inbox.iy;
          ball.vy = -ball.vy;
        }
        ball.x = nx;
        ball.y = ny;
      }
      function moveBall(){
        ctx.clearRect(box.x,box.y,box.w,box.h);
        moveBallEndCheck();
        ctx.beginPath();
        //console.log(ball.x+"\t"+ball.y+"\t"+ball.vx+"\t"+ball.vy+"\t"+(ball.x-box.r)+"\t"+(ball.y-box.r));
        ctx.drawImage(img,(ball.x-box.r),(ball.y-box.r));
        ctx.fillRect(box.x,box.y,box.r,box.h);
        ctx.fillRect((box.x+box.w-box.r),box.y,box.r,box.h);
        ctx.fillRect(box.x,box.y,box.w,box.r);
        ctx.fillRect(box.x,(box.y+box.h-box.r),box.w,box.r);
        ctx.closePath();
        ctx.fill();
      }
    </script>
  </body>
</html>

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Demo pictures

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