防止笔画边框溢出路径

发布于 2024-10-16 06:31:36 字数 1212 浏览 4 评论 0原文

planetRect(0, 0, canvasWidth, canvasHeight); 绘制一个完整的矩形，但线宽减半，这里是一个例子：

<canvas></canvas>

<script>
    var canvas = document.getElementsByTagName ("canvas");

    var lineWidth = 10;

    var canvasHeight = canvas[0].height;
    var canvasWidth = canvas[0].width;

    var ctx = canvas[0].getContext ("2d");

    ctx.lineWidth = lineWidth;

    ctx.strokeRect (0, 0, canvasWidth, canvasHeight);
</script>

问题的屏幕截图

我可以解决这个问题，但并不优雅：

<canvas></canvas>

<script>
    var canvas = document.getElementsByTagName ("canvas");

    var lineWidth = 10;

    var canvasHeight = canvas[0].height - lineWidth;
    var canvasWidth = canvas[0].width - lineWidth;

    var ctx = canvas[0].getContext ("2d");

    ctx.lineWidth = lineWidth;

    lineWidth /= 2;

    ctx.strokeRect (lineWidth, lineWidth, canvasWidth, canvasHeight);
</script>

不优雅解决方案的屏幕截图

有没有一种本地方法可以做到这一点？像“box-sizing”css3 属性之类的东西：

canvas {
    box-sizing: border-box;
}

谢谢。

原文

strokeRect (0, 0, canvasWidth, canvasHeight); draws a full rectangle but the line width is cut in half, here is an example:

<canvas></canvas>

<script>
    var canvas = document.getElementsByTagName ("canvas");

    var lineWidth = 10;

    var canvasHeight = canvas[0].height;
    var canvasWidth = canvas[0].width;

    var ctx = canvas[0].getContext ("2d");

    ctx.lineWidth = lineWidth;

    ctx.strokeRect (0, 0, canvasWidth, canvasHeight);
</script>

screenshot of problem

I can fix that but isn't elegant:

<canvas></canvas>

<script>
    var canvas = document.getElementsByTagName ("canvas");

    var lineWidth = 10;

    var canvasHeight = canvas[0].height - lineWidth;
    var canvasWidth = canvas[0].width - lineWidth;

    var ctx = canvas[0].getContext ("2d");

    ctx.lineWidth = lineWidth;

    lineWidth /= 2;

    ctx.strokeRect (lineWidth, lineWidth, canvasWidth, canvasHeight);
</script>

screenshot of inelegant solution

Is there a native method to do that ? Something like the "box-sizing" css3 attribute:

canvas {
    box-sizing: border-box;
}

Thanks.

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甜嗑 2024-10-23 06:31:36

HTML5 Canvas 中的笔画（如 Adobe Illustrator 或 SVG 中一样）始终以它们所描画的路径为中心。很久以前，我提议新的 SVG 属性听起来像您想要的，但此功能既不在 SVG 中，也不在 Canvas 中。 您的中风表现符合预期。

但是，您可以使用剪切区域，剪切到与您要描边的路径相同的位置，并将您的标称线宽：

function clippedRectStroke( ctx, x, y, w, h ){
  ctx.save();
  ctx.beginPath();
  ctx.moveTo(x,y);
  ctx.lineTo(x,y+h);
  ctx.lineTo(x+w,y+h);
  ctx.lineTo(x+w,y);
  ctx.clip();
  ctx.lineWidth *= 2;
  ctx.strokeRect(x,y,w,h);
  ctx.restore(); 
};

此处工作演示：http://jsfiddle.net/Dvz9Y/2/

Strokes in HTML5 Canvas—as in Adobe Illustrator or SVG—are always centered on the path that they are stroking. Long ago I proposed a new SVG property that sounds like what you want, but this functionality is in neither SVG nor Canvas. Your stroke is behaving as it is supposed to.

However, you can work around this by using clipping region, clipping to the same as the path you are about to stroke and doubling your nominal lineWidth:

function clippedRectStroke( ctx, x, y, w, h ){
  ctx.save();
  ctx.beginPath();
  ctx.moveTo(x,y);
  ctx.lineTo(x,y+h);
  ctx.lineTo(x+w,y+h);
  ctx.lineTo(x+w,y);
  ctx.clip();
  ctx.lineWidth *= 2;
  ctx.strokeRect(x,y,w,h);
  ctx.restore(); 
};

Working demo here: http://jsfiddle.net/Dvz9Y/2/

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