Question

我需要画一条线并给它加上边框。

我试图画两条线，一条5px和3px以上

但这似乎并不像真正的边界

const ctx = canvas.getContext('2d');
const path = new Path2D();

ctx.strokeStyle = "black";
ctx.lineWidth = 5;

path.moveTo(40, 40);
path.lineTo(50, 35);
path.lineTo(60, 40);

ctx.stroke(path);

ctx.strokeStyle = "red";
ctx.lineWidth = 3;

path.moveTo(40, 40);
path.lineTo(50, 35);
path.lineTo(60, 40);

ctx.stroke(path);

<canvas id=canvas width=100 height=100></canvas>

是否有更好的方法为线绘制边框？

Answer 1

尝试在外线设置“ endCap”：

const ctx = canvas.getContext('2d');
const path = new Path2D();

ctx.strokeStyle = "black";
ctx.lineWidth = 5;
ctx.lineCap = "butt"; // butt  round  square <-- other options

path.moveTo(40, 40);
path.lineTo(50, 35);
path.lineTo(60, 40);

ctx.stroke(path);

ctx.strokeStyle = "red";
ctx.lineWidth = 3;

path.moveTo(40, 40);
path.lineTo(50, 35);
path.lineTo(60, 40);

ctx.stroke(path);

请参阅： https://developer.mozilla.org/en-US/docs/Web/API/CanvasRenderingContext2D/lineCap

Answer 2

您可以尝试使用阴影：

const ctx = canvas.getContext('2d');

function drawPath(path) {
  ctx.lineWidth = 3;
  ctx.strokeStyle = "red";
  ctx.shadowColor = 'black';

  for (i = 0; i <= 360; i += 10) {
    a = i * Math.PI / 180
    ctx.beginPath();
    ctx.shadowOffsetX = 4 * Math.sin(a)
    ctx.shadowOffsetY = 4 * Math.cos(a)
    ctx.stroke(path);
  }
}

const path = new Path2D();
path.moveTo(20, 40);
path.lineTo(50, 35);
path.lineTo(80, 40);
path.lineTo(80, 80);
path.lineTo(160, 80);
drawPath(path);

<canvas id=canvas width=200 height=100></canvas>

这个想法是在路径对象的四周绘制稍微不同的偏移量...并且相同的逻辑可以用于图像：

https://raw.githack.com/heldersepu/hs-scripts/master/HTML/canvasOutline.html

画布绘制边框线

2 个答案: