圆形笔划上的 svg 多种颜色

Question

我想创建一个彩虹圈，如下图:

如何绘制曲线和多色停止渐变？
这是我当前的代码:

<svg width="500" height="500" xmlns="http://www.w3.org/2000/svg" xmlns:xlink="http://www.w3.org/1999/xlink">
    <defs>
    <linearGradient id="test">
    <stop offset="0%" stop-color="#f00"/>
    <stop offset="100%" stop-color="#0ff"/>
    </linearGradient>    
    </defs>    
    <circle cx="50" cy="50" r="40" fill="none" stroke="url(#test)" stroke-width="6"/>    
</svg>

Answer 1

这种方法行不通。 SVG 没有锥形渐变。要模拟效果，您必须使用大量小线段来伪造它。或者一些类似的技术。

更新:

这是一个例子。我用六个路径来近似 360 度的色调。每条路径都包含一个弧，它覆盖了圆的 60 度。我使用线性渐变从每条路径的开始到结束插入颜色。它并不完美(您可以看到颜色相交的一些不连续性)但它可能会愚弄大多数人。您可以通过使用六个以上的段来提高准确性。

    <svg xmlns="http://www.w3.org/2000/svg" version="1.1" width="100%" height="100%" viewBox="-10 -10 220 220">
      <defs>
        <linearGradient id="redyel" gradientUnits="objectBoundingBox" x1="0" y1="0" x2="1" y2="1">
            <stop offset="0%" stop-color="#ff0000"/>   
            <stop offset="100%" stop-color="#ffff00"/>   
        </linearGradient>
        <linearGradient id="yelgre" gradientUnits="objectBoundingBox" x1="0" y1="0" x2="0" y2="1">
            <stop offset="0%" stop-color="#ffff00"/>   
            <stop offset="100%" stop-color="#00ff00"/>   
        </linearGradient>
        <linearGradient id="grecya" gradientUnits="objectBoundingBox" x1="1" y1="0" x2="0" y2="1">
            <stop offset="0%" stop-color="#00ff00"/>   
            <stop offset="100%" stop-color="#00ffff"/>   
        </linearGradient>
        <linearGradient id="cyablu" gradientUnits="objectBoundingBox" x1="1" y1="1" x2="0" y2="0">
            <stop offset="0%" stop-color="#00ffff"/>   
            <stop offset="100%" stop-color="#0000ff"/>   
        </linearGradient>
        <linearGradient id="blumag" gradientUnits="objectBoundingBox" x1="0" y1="1" x2="0" y2="0">
            <stop offset="0%" stop-color="#0000ff"/>   
            <stop offset="100%" stop-color="#ff00ff"/>   
        </linearGradient>
        <linearGradient id="magred" gradientUnits="objectBoundingBox" x1="0" y1="1" x2="1" y2="0">
            <stop offset="0%" stop-color="#ff00ff"/>   
            <stop offset="100%" stop-color="#ff0000"/>   
        </linearGradient>
      </defs>
    
      <g fill="none" stroke-width="15" transform="translate(100,100)">
        <path d="M 0,-100 A 100,100 0 0,1 86.6,-50" stroke="url(#redyel)"/>
        <path d="M 86.6,-50 A 100,100 0 0,1 86.6,50" stroke="url(#yelgre)"/>
        <path d="M 86.6,50 A 100,100 0 0,1 0,100" stroke="url(#grecya)"/>
        <path d="M 0,100 A 100,100 0 0,1 -86.6,50" stroke="url(#cyablu)"/>
        <path d="M -86.6,50 A 100,100 0 0,1 -86.6,-50" stroke="url(#blumag)"/>
        <path d="M -86.6,-50 A 100,100 0 0,1 0,-100" stroke="url(#magred)"/>
      </g>
    </svg>

在这里 fiddle : http://jsfiddle.net/Weytu/

更新 2:

对于那些想要超过六个段的人，这里有一些 javascript 会产生一个你想要的任何数量的段的轮子。

function makeColourWheel(numSegments)
{
    if (numSegments <= 0)
        numSegments = 6;
    if (numSegments > 360)
        numSegments = 360;

    var  svgns = xmlns="http://www.w3.org/2000/svg";
    var  svg = document.getElementById("colourwheel");
    var  defs = svg.getElementById("defs");
    var  paths = svg.getElementById("paths");

    var  radius = 100;
    var  stepAngle = 2 * Math.PI / numSegments;

    var  lastX = 0;
    var  lastY = -radius;
    var  lastAngle = 0;
    
    for (var i=1; i<=numSegments; i++)
    {
        var  angle = i * stepAngle;

        // Calculate this arc end point
        var x = radius * Math.sin(angle);
        var y = -radius * Math.cos(angle);
        // Create a path element
        var arc = document.createElementNS(svgns, "path");
        arc.setAttribute("d", "M " + lastX.toFixed(3) + "," + lastY.toFixed(3)
                              + " A 100,100 0 0,1 " + x.toFixed(3) + "," + y.toFixed(3));
        arc.setAttribute("stroke", "url(#wheelseg" + i + ")");
        // Append it to our SVG
        paths.appendChild(arc);
        
        // Create a gradient for this segment
        var grad = document.createElementNS(svgns, "linearGradient");
        grad.setAttribute("id", "wheelseg"+i);
        grad.setAttribute("gradientUnits", "userSpaceOnUse");
        grad.setAttribute("x1", lastX.toFixed(3));
        grad.setAttribute("y1", lastY.toFixed(3));
        grad.setAttribute("x2", x.toFixed(3));
        grad.setAttribute("y2", y.toFixed(3));
        // Make the 0% stop for this gradient
        var stop = document.createElementNS(svgns, "stop");
        stop.setAttribute("offset", "0%");
        hue = Math.round(lastAngle * 360 / Math.PI / 2);
        stop.setAttribute("stop-color", "hsl(" + hue + ",100%,50%)");
        grad.appendChild(stop);
        // Make the 100% stop for this gradient
        stop = document.createElementNS(svgns, "stop");
        stop.setAttribute("offset", "100%");
        hue = Math.round(angle * 360 / Math.PI / 2);
        stop.setAttribute("stop-color", "hsl(" + hue + ",100%,50%)");
        grad.appendChild(stop);
        // Add the gradient to the SVG
        defs.appendChild(grad);

        // Update lastx/y
        lastX = x;
        lastY = y;
        lastAngle = angle;
    }
}


makeColourWheel(60);

<svg id="colourwheel" xmlns="http://www.w3.org/2000/svg" version="1.1" width="100%" height="100%" viewBox="-10 -10 220 220">
  <defs id="defs">
  </defs>

  <g id="paths" fill="none" stroke-width="15" transform="translate(100,100)">
  </g>
</svg>