javascript - Canvas 弧线绘制奇怪的形状 - CoffeeScript

Question

@.ctx.lineWidth = 20
@.ctx.moveTo(i.x, i.y)
@.ctx.arc(i.x, i.y, 3, 0, Math.PI * 2)

为什么该代码会生成上面的图像？

Answer 1

我尝试了你的弧线版本，但我发现很难理解你实际上在问什么。因此我制作了两个版本，以便直观地向您展示发生了什么。

你可以在这里查看它们! 更新的 JSFIDDLE http://jsfiddle.net/hqB6b/2/

HTML

First with the line inside.

<canvas id="ex" width="300" height="300">
This text is displayed if your browser does not support HTML5 Canvas.
</canvas>

Second with NO line inside!

<canvas id="example" width="300" height="300">
This text is displayed if your browser does not support HTML5 Canvas.
</canvas>

JS

var example = document.getElementById('example');
var ctx = example.getContext('2d');
var i = {x:100,
    y:100}
ctx.strokeStyle = '#ff0000';
ctx.lineWidth = 1;

ctx.moveTo(i.x, i.y)
//HERE BEGINPATH IS USED AFTER MOVETO
ctx.beginPath();
ctx.arc(i.x, i.y, 50, 0, Math.PI * 2)
ctx.stroke();


var ex = document.getElementById('ex');
var ct = ex.getContext('2d');
var i = {x:100,
    y:100}
ct.strokeStyle = '#ff0000';
ct.lineWidth = 1;

//HERE BEGINPATH IS USED BEFORE MOVETO
ct.beginPath();
ct.moveTo(i.x, i.y)
ct.arc(i.x, i.y, 50, 0, Math.PI * 2)
ct.stroke();