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Example of how to draw canvas polygons

小云云Original: 2018-01-31 10:55:562669browse

This article mainly introduces the relevant information about canvas polygon (spider diagram) drawing examples. The editor thinks it is quite good, so I will share it with you now and give it as a reference. Let’s follow the editor to take a look, I hope it can help everyone.

How to draw spider diagrams:

Before we start, we need to know how canvas draws images. The canvas element is used to draw graphics on web pages. HTML5's canvas element uses JavaScript to draw 2D images on a web page. On the canvas of the rectangular area, control each pixel, and use JavaScript to draw 2D graphics and render them pixel by pixel. There are many ways to use the canvas element to draw paths, rectangles, circles, characters, and add images.

* Notice! ! ! The canvas tag itself does not have drawing functions and can only use JavaScript to draw images on web pages.

The rendering is as follows:

1. Initialization js code

  //初始化
  (function(){
    var canvas = document.createElement(&#39;canvas&#39;);
    document.body.appendChild(canvas);
    canvas.height = mH;
    canvas.width = mW;
    mCtx = canvas.getContext(&#39;2d&#39;);
    drawPolygon(mCtx); // 绘制多边形边
    drawLines(mCtx); //顶点连线
    drawText(mCtx); // 绘制文本
    drawRegion(mCtx);  // 绘制数据
    drawCircle(mCtx);  // 画数据圆点
  })();

The above code , all settings are initialized through an immediate execution function. For how to draw a regular hexagon on canvas, see Drawing a regular hexagon on canvas

In the spider diagram, we can split it, By drawing hexagons, straight lines, and circles, separate complete individual components, and then call and draw them uniformly through methods

The source code is as shown below:

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>蜘蛛图canvas</title>
    <style type="text/css">
        canvas{
        }
    </style>
</head>
<body>
<script type="text/javascript">
  var mW = 400;
  var mH = 400;
  var mData = [[&#39;法力&#39;, 77],[&#39;防御&#39;, 72],[&#39;生命值&#39;, 46],[&#39;物理伤害&#39;, 50],[&#39;回复值&#39;, 80],[&#39;耐力&#39;, 60]];
  var mCount = mData.length; //边数
  var mCenter = mW /2; //中心点
  var mRadius = mCenter - 100; //半径(减去的值用于给绘制的文本留空间)
  var mAngle = Math.PI * 2 / mCount; //角度
  var mCtx = null;
  var mColorPolygon = &#39;#B8B8B8&#39;; //多边形颜色
  var mColorLines = &#39;#B8B8B8&#39;; //顶点连线颜色
  var mColorText = &#39;#000000&#39;;

  //初始化
  (function(){
    var canvas = document.createElement(&#39;canvas&#39;);
    document.body.appendChild(canvas);
    canvas.height = mH;
    canvas.width = mW;
    mCtx = canvas.getContext(&#39;2d&#39;);

    drawPolygon(mCtx);
    drawLines(mCtx);
    drawText(mCtx);
    drawRegion(mCtx);
    drawCircle(mCtx);
  })();

  // 绘制多边形边
  function drawPolygon(ctx){
    ctx.save(); // save the default state

    ctx.strokeStyle = mColorPolygon;
    var r = mRadius/ mCount; //单位半径
    //画6个圈
    for(var i = 0; i < mCount; i ++){
      ctx.beginPath(); //开始路径
      var currR = r * ( i + 1); //当前半径
      //画6条边
      for(var j = 0; j < mCount; j ++) {
        var x = mCenter + currR * Math.cos(mAngle * j);
        var y = mCenter + currR * Math.sin(mAngle * j);

        console.log(&#39;x:&#39; + x, &#39;y:&#39; + y);
        ctx.lineTo(x, y);
      }
      ctx.closePath();  //闭合路径
      ctx.stroke();
    }

    ctx.restore(); // restore to the default state
  }

  //顶点连线
  function drawLines(ctx){
    ctx.save();

    ctx.beginPath();
    ctx.strokeStyle = mColorLines;

    for(var i = 0; i < mCount; i ++){
      var x = mCenter + mRadius * Math.cos(mAngle * i);
      var y = mCenter + mRadius * Math.sin(mAngle * i);

      ctx.moveTo(mCenter, mCenter);
      ctx.lineTo(x, y);
    }

    ctx.stroke();

    ctx.restore();
  }

  //绘制文本
  function drawText(ctx){
    ctx.save();

    var fontSize = mCenter / 12;
    ctx.font = fontSize + &#39;px Microsoft Yahei&#39;;
    ctx.fillStyle = mColorText;

    for(var i = 0; i < mCount; i ++){
      var x = mCenter + mRadius * Math.cos(mAngle * i);
      var y = mCenter + mRadius * Math.sin(mAngle * i);

      if( mAngle * i >= 0 && mAngle * i <= Math.PI / 2 ){
        ctx.fillText(mData[i][0], x, y + fontSize);
      }else if(mAngle * i > Math.PI / 2 && mAngle * i <= Math.PI){
        ctx.fillText(mData[i][0], x - ctx.measureText(mData[i][0]).width, y + fontSize);
      }else if(mAngle * i > Math.PI && mAngle * i <= Math.PI * 3 / 2){
        ctx.fillText(mData[i][0], x - ctx.measureText(mData[i][0]).width, y);
      }else{
        ctx.fillText(mData[i][0], x, y);
      }

    }

    ctx.restore();
  }

  //绘制数据区域
  function drawRegion(ctx){
    ctx.save();

    ctx.beginPath();
    for(var i = 0; i < mCount; i ++){
      var x = mCenter + mRadius * Math.cos(mAngle * i) * mData[i][1] / 100;
      var y = mCenter + mRadius * Math.sin(mAngle * i) * mData[i][1] / 100;

      ctx.lineTo(x, y);
    }
    ctx.closePath();
    ctx.fillStyle = &#39;rgba(255, 0, 0, 0.5)&#39;;
    ctx.fill();

    ctx.restore();
  }
  //画点
  function drawCircle(ctx){
    ctx.save();

    var r = mCenter / 18;
    for(var i = 0; i < mCount; i ++){
      var x = mCenter + mRadius * Math.cos(mAngle * i) * mData[i][1] / 100;
      var y = mCenter + mRadius * Math.sin(mAngle * i) * mData[i][1] / 100;

      ctx.beginPath();
      ctx.arc(x, y, r, 0, Math.PI * 2);
      ctx.fillStyle = &#39;rgba(255, 0, 0, 0.8)&#39;;
      ctx.fill();
    }

    ctx.restore();
  }
</script>
</body>
</html>

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