我是Java语言的新手，所以很抱歉，如果我的错误显而易见！我正在尝试使用规范形式方程式绘制椭圆。
<html>
<body>
<canvas id="myCanvas" width="400" height="400" style="border:1px solid #000000;">
</canvas>
<script language="javaScript">
var c=document.getElementById("myCanvas");
var ctx=c.getContext("2d");
var HEIGHT = ctx.height;
var WIDTH = ctx.width;
function transform(p){
return [ WIDTH/2 + p[0], HEIGHT/2 - p[1]];
}
var a = 70; //length parallel to x axis
var b = 30; //length parallel to y axis
var h = 150 - WIDTH/2; //when tranformed this gives the pixel 150
var k = -HEIGHT/2 - 100; //when transformed this gives pixel 100
function y(x){
return b*Math.sqrt(1 - Math.pow((x - h)/a, 2)) + k;
}
var dx = a/2/100 ; //each quadrant is broken into 100 segments
var pOld = [h - a/2, k]; //starting point
var pNew = [0,0];
var x1 = 0;
var x2 = 0;
var y1 = 0;
var y2 = 0;
var temp = [0,0];
for (var i = 0; i < 100; ++i){
pNew[0] = pOld[0] + dx;
pNew[1] = y(pNew[0]);
temp = transform(pOld);
x1 = temp[0]; y1 = temp[1];
temp = transform(pNew);
x2 = temp[0]; y2 = temp[1];
ctx.moveTo(x1, y1); ctx.lineTo(x2, y2); //x1, y1 -> x2, y2
ctx.moveTo(x1, -y1); ctx.lineTo(x2, -y2); //x1,-y1 -> x2,-y2
ctx.moveTo(-x1, y1); ctx.lineTo(-x2, y2); //-x1,y1 -> -x2, y2
ctx.moveTo(-x1, -y1); ctx.lineTo(-x2, -y2); //-x1,-y1 -> -x2,-y2
pOld = pNew;
}
ctx.lineWidth = 2;
ctx.strokeStyle = "#232323";
ctx.stroke();
</script>
</body>
</html>
最佳答案
您的值为NaN（非数字）。更改这些行：
var HEIGHT = ctx.height;
var WIDTH = ctx.width;
至
var HEIGHT = c.height;
var WIDTH = c.width;
您会得到正确的号码。但是，您的
y值在画布区域之外-如果您用console.log记录值，则将看到此值。总体上似乎有一些数学问题，我在这里没有解决，但是相对于画布，您应该再走一步。关于javascript - 我在 Canvas 绘图中做错了什么？，我们在Stack Overflow上找到一个类似的问题：https://stackoverflow.com/questions/21213847/