如何使用canvas HTML5绘制一个星?
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我试图使用画布绘制一个星,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>
答案
星形基本上是正多边形,在内半径和外半径上具有交替点。
这是一个绘制星形的灵活函数的示例。
您可以设置位置,#spikes以及尖峰的内外半径:
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>
另一答案
那些函数,lineTo(),moveTo(),stroke()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。
另一答案
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();
}
另一答案
如@ v-rubinetti所述,您试图错误地调用方法。
虽然通过编码可以很容易地在画布上绘制一个简单的星形,但是绘制高级的东西很复杂。您可以使用像Inkscape这样的开源矢量图形软件以及ink2canvas扩展来绘制高级矢量图形并将它们保存到html5文档中。
例如,这是一个在Inkscape中绘制并使用ink2canvas扩展名保存的25角星形:
<!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>
另一答案
//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();
}
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