Question

我的任务是在画布上进行裁剪，我已经完成了所有逻辑，但还有一项要求尚未完成，即在选择裁剪区域时绘制虚线矩形，如：

strokeRect(x, y, width, height)

如何绘制虚线矩形？

Answer 1

这已添加到画布规范中，并非所有浏览器都已实现它，但现在是。

context.setLineDash([6]);
context.strokeRect(0, 0, 50, 50);

Answer 2

虚线没有内置功能，但这是使用自定义JS原型的示例：

HTML5 Canvas and Dashed Lines

Answer 3

参考：dotted stroke in <canvas>

 var CP = window.CanvasRenderingContext2D && CanvasRenderingContext2D.prototype;
    if (CP && CP.lineTo){
      CP.dashedLine = function(x,y,x2,y2,dashArray){
        if (!dashArray) dashArray=[10,5];
        var dashCount = dashArray.length;
        this.moveTo(x, y);
        var dx = (x2-x), dy = (y2-y);
        var slope = dy/dx;
        var distRemaining = Math.sqrt( dx*dx + dy*dy );
        var dashIndex=0, draw=true;
        while (distRemaining>=0.1){
          var dashLength = dashArray[dashIndex++%dashCount];
          if (dashLength > distRemaining) dashLength = distRemaining;
          var xStep = Math.sqrt( dashLength*dashLength / (1 + slope*slope) );
          x += xStep
          y += slope*xStep;
          this[draw ? 'lineTo' : 'moveTo'](x,y);
          distRemaining -= dashLength;
          draw = !draw;
        }
      }
    }

如何在画布中绘制虚线矩形？

3 个答案: