How does QGIS render SVG symbols?

Question

I'm a bit confused about SVG graphics! I'm trying to build a script that creates a "north reference" in SVG, and it renders fine when viewed in Firefox. In Inkscape there's some issues with text orientation (the "GN" marker, but I can fix that), but in QGIS it renders really bad.

<?xml version="1.0" standalone="no"?>
<!DOCTYPE svg PUBLIC "-//W3C//DTD SVG 1.1//EN" 
  "http://www.w3.org/Graphics/SVG/1.1/DTD/svg11.dtd">
<svg width="5cm" height="5cm" viewBox="0 0 400 400"
     xmlns="http://www.w3.org/2000/svg" version="1.1">
  <title>North Arrows</title>
  <defs
    id="arrowheads">
    <marker
     style="overflow:visible"
     id="magnetic"
     refX="0.0"
     refY="0.0"
     orient="auto">
     <path d="M 5 0 L 40 0 L 5 7 z"
        stroke="#000" stroke-width="1" fill="#000" />
    </marker>
    <marker
     style="overflow:visible"
     id="true"
     refX="0.0"
     refY="0.0"
     orient="auto">
     <path
        transform="scale(0.8)"
        d="M 0 -10 L 35 0 L 0 10 L 22 -18 L 22 18 z"
        stroke="#000" stroke-width="1" fill="#000" />
    </marker>
    <marker
     style="overflow:visible"
     id="grid"
     refX="0.0"
     refY="0.0"
     orient="auto">
     <text
        style="font-size:20px;font-family:sans-serif;writing-mode: tb;"
        >
         <tspan
         y="-15"
         x="10"
         id="grid_text">GN</tspan> 
        </text>
    </marker>
  </defs>
  <path d="M 200 380 L 230 90"
        stroke="#000" stroke-width="1" 
        style="marker-end:url(#magnetic)" />
  <path d="M 200 380 L 180 60"
        stroke="#000" stroke-width="1"
        style="marker-end:url(#true)" />
  <path d="M 200 380 L 200 30"
        stroke="#000" stroke-width="1"
        style="marker-end:url(#grid)" />
  <text y="395" style="font-size:15px;font-family:sans-serif;" >
        <tspan x="220" dy="-15">GN = 0</tspan>
        <tspan x="220" dy="-15" >Magnetic Dev. 20</tspan>
        <tspan x="220" dy="-15" >True North = 10</tspan>
  </text>
</svg>

When I preview or open in Firefox it looks like this:

But when I add the image in QGIS (Composer) it looks like this:

Does QGIS have a limited SVG rendering capability, or is it Qt that has limitations? Isn't my SVG in a "valid" format/syntax?

[Edit] I'm leaning towards a Qt problem, since "karbon" (Qt vector application) previews the file fine, but when opening it, it displays the same as in QGIS. When creating a line with arrow markers in karbon and saving as SVG, markers are lost! Is Qt really this bad at rendering SVG??

Answer 1

Well. It turns out QtSvg (and thereby QGIS) only supports SVG "Tiny" 1.2. Description for Tiny

One of the things that "Tiny" doesn't support is "markers"...

I need to generate my "arrowheads" as separate polygons, place and rotate them manually...

Work is on the way.