带有HTML5画布中间的孔的多边形 [英] Polygon with a hole in the middle with HTML5's canvas
问题描述
使用< canvas>
标记我需要能够在多边形中绘制一个洞。
现在我有一件非常简单的事情,它使用beginPath(),然后为每个点执行lineTo()。然后填充fill()。
我看不出有什么方法可以填充一个填充的多边形,虽然中间没有填充,就像一个甜甜圈一样。
我没有做甜甜圈,但它适用于这个例子。
有什么我失踪了吗?
我宁愿不把它填满,然后重新绘制中间。
这就是我所做的work:
var ctx = canvas.getContext(2d);
ctx.beginPath();
// polygon1 ---通常是外部多边形,必须是顺时针
ctx.moveTo(0,0);
ctx.lineTo(200,0);
ctx.lineTo(200,200);
ctx.lineTo(0,200);
ctx.lineTo(0,0);
ctx.closePath();
// polygon2 ---通常是孔,必须是逆时针
ctx.moveTo(10,10);
ctx.lineTo(10,100);
ctx.lineTo(100,100);
ctx.lineTo(100,10);
ctx.lineTo(10,10);
ctx.closePath();
//根据需要添加许多孔
ctx.fillStyle =#FF0000;
ctx.strokeStyle =rgba(0.5,0.5,0.5,0.5);
ctx.lineWidth = 1;
ctx.fill();
ctx.stroke();
这里的主要思想是您只能使用beginPath一次;外面的多边形必须是顺时针的,孔必须是逆时针的。
Using the <canvas>
tag I need to be able to draw a hole in a polygon.
Right now I have something very simple that uses beginPath() then does lineTo() for each point. It is then filled with fill().
I cannot see any way to have a filled polygon with a unfilled middle though, like a donut. I'm not making a donut but it is suitable for this example.
Is there something I am missing? I would rather not draw it fully filled then have to redraw the middle.
This is what i made it work:
var ctx = canvas.getContext("2d");
ctx.beginPath();
//polygon1--- usually the outside polygon, must be clockwise
ctx.moveTo(0, 0);
ctx.lineTo(200, 0);
ctx.lineTo(200, 200);
ctx.lineTo(0, 200);
ctx.lineTo(0, 0);
ctx.closePath();
//polygon2 --- usually hole,must be counter-clockwise
ctx.moveTo(10, 10);
ctx.lineTo(10,100);
ctx.lineTo(100, 100);
ctx.lineTo(100, 10);
ctx.lineTo(10, 10);
ctx.closePath();
// add as many holes as you want
ctx.fillStyle = "#FF0000";
ctx.strokeStyle = "rgba(0.5,0.5,0.5,0.5)";
ctx.lineWidth = 1;
ctx.fill();
ctx.stroke();
The main idea here is you can only use beginPath once; the outside polygon must be clockwise and holes must be counter-clockwise.
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