如何使用SVG滤镜创建模糊的标签背景？

Question

我希望有一个很好的解决以下问题的方法：

在条形图上，条形填充有不同但未知的颜色，我希望将标签固定为黑色，以便于阅读。

我正在搜索的方法应该看起来像在图像窗口的标题栏中。标签为黑色，位于模糊的白色背景上，该背景位于任何颜色的条形顶部。

是否有使用SVG过滤器的方法？

下面是我尝试过的一些方法：

    .black {
      fill: black;
    }
    .blue {
      fill: blue;
    }
    .red {
      fill: red;
    }    
    .yellow {
      fill: yellow;
    }
    .label{
      fill: black;
      font-size: 14px;
    }
    .label-background{
      fill: white;
      font-size: 16px;
    }
    .text-background{
      paint-order: stroke;
      stroke: #fff;
      fill: black;
      stroke-width: 5px;
    }
    .header{
      font-size: 20px;
    }
    .background{
      fill: white;
      opacity: 0.6;
    }

  <svg width="500" height="500">
    <defs>
      <filter x="-0.05" y="-0.1" width="1.08" height="1.2" id="solid">
        <feFlood flood-color="lightgrey"/>
        <feComposite in="SourceGraphic" operator="xor" />
      </filter>
    </defs>

    <g class="row-1" transform="translate(0,30)">
      <text class="header" x="20" y="-10">text label on top of bar </text>
      <g>
        <rect class="black" width=100 height=30></rect>
        <text class="label" x="20" y="20">my text label</text>
      </g>

      <g transform="translate(120,0)">
        <rect class="blue" width=100 height=30></rect>
        <text class="label" x="20" y="20">my text label</text>
      </g>

      <g transform="translate(240,0)">
        <rect class="red" width=100 height=30></rect>
        <text class="label" x="20" y="20">my text label</text>
      </g>

      <g transform="translate(360,0)">
        <rect class="yellow" width=100 height=30></rect>
        <text class="label" x="20" y="20">my text label</text>
      </g>
    </g>  
    
		<g class="row-2" transform="translate(0,100)">
      <text class="header" x="20" y="-10">text label on top of rect.background on top of bar </text>
      <g>
        <rect class="black" width=100 height=30></rect>
        <rect class="background" x=17 y=6 width=78 height=19></rect>
        <text class="label" x="20" y="20">my text label</text>
      </g>

      <g transform="translate(120,0)">
        <rect class="blue" width=100 height=30></rect>
        <rect class="background" x=17 y=6 width=78 height=19></rect>
        <text class="label" x="20" y="20">my text label</text>
      </g>

      <g transform="translate(240,0)">
        <rect class="red" width=100 height=30></rect>
        <rect class="background" x=17 y=6 width=78 height=19></rect>
        <text class="label" x="20" y="20">my text label</text>
      </g>

      <g transform="translate(360,0)">
        <rect class="yellow" width=100 height=30></rect>
        <rect class="background" x=17 y=6 width=78 height=19></rect>
        <text class="label" x="20" y="20">my text label</text>
      </g>
  	</g>
    
    <g class="row-3" transform="translate(0, 170)">
      <text class="header" x="20" y="-10">text label with filter #solid on top of bar </text>
      <g>
        <rect class="black" width=100 height=30></rect>
        <text class="label" filter="url(#solid)" x="20" y="20">my text label</text>
      </g>

      <g transform="translate(120,0)">
        <rect class="blue" width=100 height=30></rect>
        <text class="label" filter="url(#solid)" x="20" y="20">my text label</text>
      </g>

      <g transform="translate(240,0)">
        <rect class="red" width=100 height=30></rect>
        <text class="label" filter="url(#solid)" x="20" y="20">my text label</text>
      </g>

      <g transform="translate(360,0)">
        <rect class="yellow" width=100 height=30></rect>
        <text class="label" filter="url(#solid)" x="20" y="20">my text label</text>
      </g>
    </g> 

    <g class="row-4" transform="translate(0, 240)">
      <text class="header" x="20" y="-10">text label on top of larger text label with background color on top of bar </text>
      <g>
        <rect class="black" width=100 height=30></rect>
        <text class="label-background" x="18" y="22">my text label</text>
        <text class="label" x="20" y="20">my text label</text>
      </g>

      <g transform="translate(120,0)">
        <rect class="blue" width=100 height=30></rect>
        <text class="label-background" x="18" y="22">my text label</text>
        <text class="label" x="20" y="20">my text label</text>
      </g>

      <g transform="translate(240,0)">
        <rect class="red" width=100 height=30></rect>
        <text class="label-background" x="18" y="22">my text label</text>
        <text class="label" x="20" y="20">my text label</text>
      </g>

      <g transform="translate(360,0)">
        <rect class="yellow" width=100 height=30></rect>
        <text class="label-background" x="18" y="22">my text label</text>
        <text class="label" x="20" y="20">my text label</text>
      </g>
    </g> 
    
    <g class="row-5" transform="translate(0, 310)">
      <text class="header" x="20" y="-10">text label with paint-order: stroke on top of bar </text>
      <g>
        <rect class="black" width=100 height=30></rect>
        <text class="label text-background" x="20" y="20">my text label</text>
      </g>

      <g transform="translate(120,0)">
        <rect class="blue" width=100 height=30></rect>
        <text class="label text-background" x="20" y="20">my text label</text>
      </g>

      <g transform="translate(240,0)">
        <rect class="red" width=100 height=30></rect>
        <text class="label text-background" x="20" y="20">my text label</text>
      </g>

      <g transform="translate(360,0)">
        <rect class="yellow" width=100 height=30></rect>
        <text class="label text-background" x="20" y="20">my text label</text>
      </g>
    </g> 
  </svg>
  

Answer 1

未经充分测试，但使用多个值构建text-shadow具有所需的效果：

    svg text {
      text-shadow: 0px 0px 2px white,
                   0px 0px 4px white,
                   0px 0px 6px white,
                   0px 0px 8px white,
                   0px 0px 10px white;
    }

工作示例：

    .black {
      fill: black;
    }
    .blue {
      fill: blue;
    }
    .red {
      fill: red;
    }    
    .yellow {
      fill: yellow;
    }
    .label{
      fill: black;
      font-size: 14px;
    }

svg g.row-1 text {
  text-shadow: 0px 0px 2px white,
               0px 0px 4px white,
               0px 0px 6px white,
               0px 0px 8px white,
               0px 0px 10px white;
}

<svg width="500" height="500">
    <defs>
      <filter x="-0.05" y="-0.1" width="1.08" height="1.2" id="solid">
        <feFlood flood-color="lightgrey"/>
        <feComposite in="SourceGraphic" operator="xor" />
      </filter>
    </defs>

    <g class="row-1" transform="translate(0,30)">
      <g>
        <rect class="black" width=100 height=30></rect>
        <text class="label" x="20" y="20">my text label</text>
      </g>

      <g transform="translate(120,0)">
        <rect class="blue" width=100 height=30></rect>
        <text class="label" x="20" y="20">my text label</text>
      </g>

      <g transform="translate(240,0)">
        <rect class="red" width=100 height=30></rect>
        <text class="label" x="20" y="20">my text label</text>
      </g>

      <g transform="translate(360,0)">
        <rect class="yellow" width=100 height=30></rect>
        <text class="label" x="20" y="20">my text label</text>
      </g>
    </g>  
</svg>
  

Answer 2

由于您正在寻求SVG过滤器解决方案：

1. 以SourceAlpha开始，为您提供元素（即文本）的黑色轮廓，然后用feGaussianBlur将其模糊以创建柔和的阴影。
2. 此阴影将为黑色，因此请使用feColorMatrix将其变为白色。
3. 最后，使用feBlend将原始文本放在阴影上方。

参考：

• SVG Drop Shadows（请参阅示例3）
• Finessing feColorMatrix

.black {
  fill: black;
}
.blue {
  fill: blue;
}
.red {
  fill: red;
}    
.yellow {
  fill: yellow;
}
.label {
  fill: black;
  font-size: 14px;
}

<svg width="500" height="80">
  <defs>
    <filter id="shadow">
      <feGaussianBlur in="SourceAlpha" stdDeviation="3" result="blur" />
      <feColorMatrix in="blur" type="matrix" values="0  0  0  0  1
                                                     0  0  0  0  1
                                                     0  0  0  0  1
                                                     0  0  0  8  0" result="white" />
      <feColorMatrix in="white" type="matrix" values="1  0  0  0  0
                                                      0  1  0  0  0
                                                      0  0  1  0  0
                                                      0  0  0 .8  0" result="dim" />
      <feBlend in="SourceGraphic" in2="dim" mode="normal" />
    </filter>
  </defs>

  <g class="row-1" transform="translate(10,30)">
    <text class="header" x="0" y="-10">feGaussianBlur on SourceAlpha</text>
    <g>
      <rect class="black" width=100 height=30></rect>
      <text class="label" x="20" y="20" filter="url(#shadow)">my text label</text>
    </g>
    <g transform="translate(120,0)">
      <rect class="blue" width=100 height=30></rect>
      <text class="label" x="20" y="20" filter="url(#shadow)">my text label</text>
    </g>
    <g transform="translate(240,0)">
      <rect class="red" width=100 height=30></rect>
      <text class="label" x="20" y="20" filter="url(#shadow)">my text label</text>
    </g>
    <g transform="translate(360,0)">
      <rect class="yellow" width=100 height=30></rect>
      <text class="label" x="20" y="20" filter="url(#shadow)">my text label</text>
    </g>
  </g>  
</svg>