使用for循环绘制HTML5画布圆

Question

I am trying to draw circles using a for loop. It works just fine accept it double draws the last circle. See this jsfiddle for the example.

If I comment out the last context.stroke(); in the second 'for' loop the circles display correctly. If I leave it in it double draws the last circle making it look bold.

What am I doing wrong?

Ken

Answer 1

The duplicate is caused by the extension lines you are drawing after the circles. Add a context.beginPath() call in the last for loop:

for(var j = 0; j < circle_Count + 1; j++) {
  context.beginPath();
  ...

Answer 2

Working fiddle: http://jsfiddle.net/kwwqw5n2/3/

You have to close paths.

var canvas = document.getElementById('myCanvas');
var context = canvas.getContext('2d');
var box_Height = 50;

// Make Top Rect
context.fillStyle = "#F3E2A9";
context.fillRect(1, 1, canvas.width-1, box_Height-1);
context.strokeRect(0.5, 0.5, canvas.width-1, box_Height);

//Define the circles
var centerY = 25;
var radius = 10;
var circle_Count = 3;
var distance_Between = canvas.width / (circle_Count+1);

//Draw three white circles.
for(var i=0;i<circle_Count;i++){
   context.beginPath();
   context.arc(distance_Between * (i+1), centerY, radius, 0, 2 * Math.PI, true);
   context.fillStyle = 'white';
   context.lineWidth = 1;
   context.strokeStyle = '#000000';
   context.fill();
   context.stroke();
   context.closePath();
}
//Define the Extension Lines
var Ext_Line_Start_X = 0;
var Ext_Line_Start_Y = box_Height + 4;  //The plus is the Gap
var Ext_Line_Length = 60;

//Draw Extension Lines
for(var j=0;j<circle_Count+1;j++){
    context.beginPath();
    context.moveTo(distance_Between * j + 0.5, Ext_Line_Start_Y);
    context.lineTo(distance_Between * j + 0.5, Ext_Line_Start_Y + Ext_Line_Length);
    context.stroke();
    context.closePath();
}