canvas - 基礎知識 - 虛線的繪制

主要的JS邏輯代碼：

// 虛線的繪制
var context = document.getElementById('canvas').getContext('2d');

function drawDashLine(context, x1, y1, x2, y2, dashLength) {
  dashLength = dashLength === undefined ? 5 : dashLength

   var deltaX = x2 - x1;
   var deltaY = y2 - y1;
   var numDashes = Math.floor(
     Math.sqrt(deltaX * deltaX + deltaY * deltaY) / dashLength
   )
   for(var i = 0; i < numDashes; i++) {
     context[ i % 2 === 0 ? 'moveTo' : 'lineTo']
     (x1 + (deltaX / numDashes) * i, y1 + (deltaY / numDashes) * i);
   }
   context.stroke();
}

context.lineWidth = 3;
context.strokeStyle = 'blue';
drawDashLine(context, 20, 20, context.canvas.width - 20, 20);
drawDashLine(context, context.canvas.width - 20, 20, context.canvas.width - 20, context.canvas.height - 20, 10);
drawDashLine(context, context.canvas.width -20, context.canvas.height - 20, 20, context.canvas.height - 20, 15);
drawDashLine(context, 20, context.canvas.height - 20, 20 , 20, 2);
           

效果圖如下：