SVG filter feGaussianBlur in percentage

Question

Is it possible to set the feGaussianBlur in %?

I don't know why but this does not work.

<filter id="drop-shadow"> 
  <feGaussianBlur in="SourceAlpha" stdDeviation="0.09"/>
     <feOffset dx="52%" dy="2%" result="offsetblur"/>
        <feFlood flood-color="#000000"/> 
        <feComposite in2="offsetblur" operator="in"/>
        <feMerge> 
        <feMergeNode/> 
     <feMergeNode in="SourceGraphic"/>
   </feMerge> 
</filter>

Answer 1

Paul and Robert mean the following:

<filter id="drop-shadow" primitiveUnits="objectBoundingBox"> 
  <feGaussianBlur in="SourceAlpha" stdDeviation="0.09"/>
     <feOffset dx="0.52" dy="0.02" result="offsetblur"/>
        <feFlood flood-color="#000000"/> 
        <feComposite in2="offsetblur" operator="in"/>
        <feMerge> 
        <feMergeNode/> 
     <feMergeNode in="SourceGraphic"/>
   </feMerge> 
</filter>

That is a very big blur and a very big offset in % terms, so you're going to have to expand the filter region a lot.

<svg width="800" height="800">
      <defs>
        <filter id="blurme" primitiveUnits="objectBoundingBox" x="-50%" y="-50%" width="300%" height="200%"> 
         <feGaussianBlur in="SourceAlpha" stdDeviation="0.09"/>
         <feOffset dx="0.52" dy="0.02" result="offsetblur"/>
            <feFlood flood-color="black"/> 
            <feComposite in2="offsetblur" operator="in"/>
            <feMerge> 
            <feMergeNode/> 
            <feMergeNode in="SourceGraphic"/>
       </feMerge> 
    </filter>
      </defs>
      <rect filter="url(#blurme)" x="100" y="100" width="300" height="300" fill="red"/>
    </svg>

Answer 2

The SVG specification says that only numbers are allowed, although if you use objectBoundingBox the number is effectively a percentage of the object's size. There's an example of filterPrimitiveUnits in the SVG specification