如何将笔划设置在特定的一侧？

Question

有没有办法只在画布对象的一侧进行描边？例如，我只想对顶部进行描边。

当我应用"strokeWidth:1"时，它适用于所有方面。我没有找到任何属性或方法来解决我的问题。

Answer 1

对于已定义的边，它没有任何方法。您可以在图像后面添加一个矩形，使其看起来像一个边框。例如“上边框”宽度10px

var canvas = new fabric.Canvas('c');
var radius = 150;

fabric.Image.fromURL('http://cdn.younghollywood.com/images/stories/newsIMG/wenn/20140901/wenn21338105_46_4145_8.jpg', function(oImg) {
    oImg.scale(1.0).set({
        left: 50,
        top: 50,
        width: 200,
        height: 200
    });

    canvas.add(oImg);
    canvas.renderAll();
});

var border = new fabric.Rect({ 
    width: 200, 
    height: 200+10, 
    left: 50, 
    top: 40,
    fill: "#FFFFFF"
});

canvas.add(border);
canvas.renderAll();

小提琴：http://jsfiddle.net/q6Y6k/11/

否则，请检查以下内容：How to set a stroke-width:1 on only certain sides of SVG shapes?

Answer 2

我找到了一个使用strokeDashArray的解决方案。

var canvas = new fabric.Canvas('c');

var border = new fabric.Rect({ 
    width: 200, 
    height: 100, 
    left: 50, 
    top: 40,
    fill: "#FFFFFF",
    strokeWidth: 1,
    stroke: '#333',
    strokeDashArray: [200, 100] // same as [width, height]

});

canvas.add(border);
canvas.renderAll();

jsFiddle的答案是here。

基于这个答案，你可以找到任何类型的自定义边框的解决方案。

Answer 3

遇到相同的问题。我必须覆盖_render()方法并单独绘制线条，而不是一次性绘制所有线条。

let canvas = new fabric.Canvas("my-canvas");
canvas.setBackgroundColor("#ccc");

fabric.RectWithBorders = fabric.util.createClass(fabric.Rect, {
  type: "rectWithBorders",
  borderTop: true,
  borderBottom: true,
  borderLeft: true,
  borderRight: false,

  initialize: function (options, borderOptions) {
    this.callSuper("initialize", options);
    this.borderTop = borderOptions.borderTop;
    this.borderBottom = borderOptions.borderBottom;
    this.borderLeft = borderOptions.borderLeft;
    this.borderRight = borderOptions.borderRight;
 },
 _render: function (ctx) {
    const originalStroke = this.stroke;
    var rx = this.rx ? Math.min(this.rx, this.width / 2) : 0,
    ry = this.ry ? Math.min(this.ry, this.height / 2) : 0,
    w = this.width,
    h = this.height,
    x = -this.width / 2,
    y = -this.height / 2,
    isRounded = rx !== 0 || ry !== 0,
    k = 1 - 0.5522847498;

// Border Top
ctx.beginPath();
this.stroke = this.borderTop ? originalStroke : null;
ctx.moveTo(x + rx, y);
ctx.lineTo(x + w - rx, y);
isRounded &&
  this.borderRight &&
  ctx.bezierCurveTo(x + w - k * rx, y, x + w, y + k * ry, x + w, y + ry);
ctx.moveTo(x + w, y + h - ry);
ctx.closePath();
this._renderPaintInOrder(ctx);

// Border Right
ctx.beginPath();
this.stroke = this.borderRight ? originalStroke : null;
ctx.moveTo(x + w, y + ry);
ctx.lineTo(x + w, y + h - ry);
isRounded &&
  this.borderBottom &&
  ctx.bezierCurveTo(
    x + w,
    y + h - k * ry,
    x + w - k * rx,
    y + h,
    x + w - rx,
    y + h
  );
ctx.moveTo(x + rx, y + h);
ctx.closePath();
this._renderPaintInOrder(ctx);

// Border Bottom
ctx.beginPath();
this.stroke = this.borderBottom ? originalStroke : null;
ctx.moveTo(x + w - rx, y + h);
ctx.lineTo(x + rx, y + h);
isRounded &&
  this.borderLeft &&
  ctx.bezierCurveTo(x + k * rx, y + h, x, y + h - k * ry, x, y + h - ry);
ctx.moveTo(x, y + ry);
ctx.closePath();
this._renderPaintInOrder(ctx);

// Border Left
ctx.beginPath();
this.stroke = this.borderLeft ? originalStroke : null;
ctx.moveTo(x, y + h - ry);
ctx.lineTo(x, y + ry);
isRounded &&
  this.borderTop &&
  ctx.bezierCurveTo(x, y + k * ry, x + k * rx, y, x + rx, y);
ctx.moveTo(x + w - rx, y);
ctx.closePath();

this._renderPaintInOrder(ctx);
}
});

canvas.add(
  new fabric.RectWithBorders({
   width: 150,
   height: 150,
   left: 25,
   top: 25,
   fill: "transparent",
   strokeWidth: 1,
   stroke: "#333"
   }, 
   {borderTop: false, borderBottom: true,
    borderLeft: true, borderRight: true})
 );

不确定这会对性能造成多大影响。还没有完全测试，因为以后不需要这样做。

对于演示，fabricjs border sides可以检查此代码