Question

我试图使用画布绘制一个星星，但代码没有运行。我想了解：测量Y和X坐标的步骤是什么？怎么找到他们？绘制任何形状？

<html>
 <head>
   <meta charset = "utf-8">
   <title>Drawing Lines</title>
 </head>
 <body>
   <canvas id = "drawLines" width = "400" height = "200" 
     style = "border: 1px solid Black;">
   </canvas>
   <script>
     var canvas = document.getElementById("drawLines");
     var context = canvas.getContext("2d")

     canvas.beginPath(); 
     canvas.moveTo(50,50);
     canvas.lineTo(120,150);
     canvas.lineTo(0,180); 
     canvas.lineTo(120,210);
     canvas.lineTo(50,310);  
     canvas.lineTo(160,250);
     canvas.lineTo(190,370);
     canvas.lineTo(220,250);
     canvas.lineTo(330,310);
     canvas.lineTo(260,210);
     canvas.lineTo(380,180);
     canvas.closePath();
     canvas.stroke();
   </script>
 </body>
</html>

Answer 1

星形基本上是一个正多边形，在内半径和外半径上有交替点。

这是一个绘制星形的灵活函数示例。

您可以设置位置，＃spikes和内部＆amp;钉的外半径：

enter image description here

示例代码和演示：http://jsfiddle.net/m1erickson/8j6kdf4o/

<!doctype html>
<html>
<head>
<link rel="stylesheet" type="text/css" media="all" href="css/reset.css" /> <!-- reset css -->
<script type="text/javascript" src="http://code.jquery.com/jquery.min.js"></script>
<style>
    body{ background-color: ivory; }
    canvas{border:1px solid red;}
</style>
<script>
$(function(){

    var canvas=document.getElementById("canvas");
    var ctx=canvas.getContext("2d");

    function drawStar(cx,cy,spikes,outerRadius,innerRadius){
      var rot=Math.PI/2*3;
      var x=cx;
      var y=cy;
      var step=Math.PI/spikes;

      ctx.beginPath();
      ctx.moveTo(cx,cy-outerRadius)
      for(i=0;i<spikes;i++){
        x=cx+Math.cos(rot)*outerRadius;
        y=cy+Math.sin(rot)*outerRadius;
        ctx.lineTo(x,y)
        rot+=step

        x=cx+Math.cos(rot)*innerRadius;
        y=cy+Math.sin(rot)*innerRadius;
        ctx.lineTo(x,y)
        rot+=step
      }
      ctx.lineTo(cx,cy-outerRadius);
      ctx.closePath();
      ctx.lineWidth=5;
      ctx.strokeStyle='blue';
      ctx.stroke();
      ctx.fillStyle='skyblue';
      ctx.fill();
    }

    drawStar(100,100,5,30,15);

}); // end $(function(){});
</script>
</head>
<body>
    <canvas id="canvas" width=300 height=300></canvas>
</body>
</html>

Answer 2

这些函数，lineTo（），moveTo（），stroke（）等等属于上下文对象，而不是canvas对象。你在检查你的开发者控制台（Chrome中的f12）吗？您会看到这些函数未定义。

Answer 3

使用坐标转换功能可以更短：

function strokeStar(x, y, r, n, inset) {
    ctx.save();
    ctx.beginPath();
    ctx.translate(x, y);
    ctx.moveTo(0,0-r);
    for (var i = 0; i < n; i++) {
        ctx.rotate(Math.PI / n);
        ctx.lineTo(0, 0 - (r*inset));
        ctx.rotate(Math.PI / n);
        ctx.lineTo(0, 0 - r);
    }
    ctx.closePath();
    ctx.fill();
    ctx.restore();
}

Answer 4

如@ v-rubinetti所述，您试图错误地调用方法。

虽然通过编码在画布上绘制一个简单的星很容易，但绘制高级内容很复杂。您可以使用开源矢量图形软件（如Inkscape）和ink2canvas扩展名来绘制高级矢量图形并将其保存为html5文档。

例如，这是一个在Inkscape中绘制的25角星形，并使用ink2canvas扩展名保存：

<!DOCTYPE html>
<html>
<head>
    <meta http-equiv="Content-Type" content="text/html; charset=UTF-8" />
    <title>Inkscape Output</title>
</head>
<body>
    <canvas id='canvas' width='320' height='320'></canvas>
    <script>
    var ctx = document.getElementById("canvas").getContext("2d");
    ctx.save();
    ctx.lineJoin = 'miter';
    ctx.strokeStyle = 'rgb(0, 0, 0)';
    ctx.lineCap = 'butt';
    ctx.lineWidth = 1.000000;
    ctx.fillStyle = 'rgb(255, 255, 0)';
    ctx.beginPath();
    ctx.transform(0.506236, 0.000000, 0.000000, 0.505711, 82.274469, 51.410524);
    ctx.moveTo(342.857130, 449.505040);
    ctx.lineTo(234.764940, 344.516400);
    ctx.lineTo(279.468630, 488.419550);
    ctx.lineTo(200.881970, 359.847880);
    ctx.lineTo(208.393950, 510.347410);
    ctx.lineTo(164.250710, 366.271350);
    ctx.lineTo(134.098980, 513.910810);
    ctx.lineTo(127.172840, 363.383190);
    ctx.lineTo(61.251941, 498.885850);
    ctx.lineTo(91.978093, 351.364870);
    ctx.lineTo(-5.569921, 466.216610);
    ctx.lineTo(60.877887, 330.971560);
    ctx.lineTo(-62.167941, 417.955810);
    ctx.lineTo(35.826363, 303.484630);
    ctx.lineTo(-104.985860, 357.135850);
    ctx.lineTo(18.397601, 270.631190);
    ctx.lineTo(-131.333260, 287.578290);
    ctx.lineTo(9.686712, 234.475540);
    ctx.lineTo(-139.554650, 213.653670);
    ctx.lineTo(10.241036, 197.289490);
    ctx.lineTo(-129.133450, 140.006950);
    ctx.lineTo(20.025741, 161.409550);
    ctx.lineTo(-100.724450, 71.265628);
    ctx.lineTo(38.426018, 129.090210);
    ctx.lineTo(-56.112700, 11.748970);
    ctx.lineTo(64.285711, 102.362200);
    ctx.lineTo(1.898679, -34.803371);
    ctx.lineTo(95.979959, 82.904945);
    ctx.lineTo(69.664621, -65.466342);
    ctx.lineTo(131.517300, 71.941014);
    ctx.lineTo(142.927140, -78.313274);
    ctx.lineTo(168.664780, 70.159311);
    ctx.lineTo(217.082890, -72.536949);
    ctx.lineTo(205.088300, 77.671789);
    ctx.lineTo(287.472380, -48.500313);
    ctx.lineTo(238.499240, 94.006409);
    ctx.lineTo(349.672790, -7.713676);
    ctx.lineTo(266.798250, 118.136810);
    ctx.lineTo(399.775840, 47.260185);
    ctx.lineTo(288.207210, 148.546780);
    ctx.lineTo(434.633360, 112.967060);
    ctx.lineTo(301.380910, 183.325570);
    ctx.lineTo(452.055130, 185.278350);
    ctx.lineTo(305.491610, 220.287880);
    ctx.lineTo(450.946490, 259.650470);
    ctx.lineTo(300.281000, 257.111240);
    ctx.lineTo(431.377070, 331.410340);
    ctx.lineTo(286.076510, 291.481900);
    ctx.lineTo(394.576520, 396.049020);
    ctx.lineTo(263.770630, 321.240230);
    ctx.closePath();
    ctx.fill();
    ctx.stroke();
    ctx.restore();
    </script>
</body>
</html>

Answer 5

//function to draw star with N spikes
//centered on a circle of radius R, centered on (cX,cY)
function star(R, cX, cY, N) {
  //star draw
  ctx.beginPath();
  ctx.moveTo(cX + R,cY);
  for(var i = 1; i <= N * 2; i++)
  {
    if(i % 2 == 0){
      var theta = i * (Math.PI * 2) / (N * 2);
      var x = cX + (R * Math.cos(theta));
      var y = cY + (R * Math.sin(theta));
    } else {
      var theta = i * (Math.PI * 2) / (N * 2);
      var x = cX + ((R/2) * Math.cos(theta));
      var y = cY + ((R/2) * Math.sin(theta));
    }

    ctx.lineTo(x ,y);
  }
  ctx.closePath();
  ctx.stroke();
}

如何使用canvas HTML5绘制一个星？

5 个答案: