如何在畫布上繪製虛線矩形？

Question

我負責做帆布剪裁和我與所有的邏輯完成，但一個要求是尚未完成，即畫出一個虛線框，而選擇裁剪區域，如：

strokeRect(x, y, width, height) 

我怎樣才能畫一個虛線的矩形？

Answer 1

有沒有在功能上沒有專爲虛線，但在這裏我們用自定義JS原型的例子：

HTML5 Canvas and Dashed Lines

Answer 2

參見：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; 
     } 
     } 
    } 

Answer 3

這已被添加到畫布規範，並非所有的瀏覽器都已經實現了它，但在這裏。

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