Implement remaining filter primitives

[weisJ]

• [x] feComponentTransfer
  • feFuncA
  • feFuncB
  • feFuncG
  • feFuncR
• [ ] feConvolveMatrix
• [ ] feDiffuseLighting
• [x] feDropShadow
• [ ] feDistantLight
• [ ] feImage
• [ ] feMorphology
• [ ] fePointLight
• [ ] feSpecularLighting
• [ ] feSpotLight
• [ ] feTile

feTile and feImage first require proper handling of filter primitive regions #70.

[stanio]

I think <feDropShadow> would be a nice addition, as it is a convenient shorthand for commonly used effect. Possibly implemented as translation to existing primitives, as suggested by the spec.

For <feImage> there's the (separate) use case of using SVG fragment as a source: <feImage href="#graphic1" />. It doesn't appear supported by Firefox currently (Bug #455986), but it is handled in Chrome. While there are alternative (more complex) ways to achieve the following, here's an example I would like to share – Have an object cast a shadow only over another one:

filter-mask.svg

<svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 256 256">
  <defs>
    <filter id="shadow-on-graphic1" x="0" y="0" width="100%" height="100%" filterUnits="userSpaceOnUse">
      <feGaussianBlur in="SourceAlpha" stdDeviation="5" />
      <feOffset dx="5" dy="10" result="offset-blur" />
      <feImage href="#graphic1" result="graphic1" />
      <feFlood flood-color="black" flood-opacity="0.5" />
      <feComposite in2="offset-blur" operator="in" />
      <feComposite in2="graphic1" operator="in" result="masked-shadow" />
      <feComposite in="SourceGraphic" in2="masked-shadow" operator="over" />
    </filter>
  </defs>

  <rect id="graphic1" x="13" y="13" width="120" height="230" fill="green" />

  <circle cx="110" cy="130" r="70" fill="orange" filter="url(#shadow-on-graphic1)" />

</svg>

Reference image from Batik (after translating href → xlink:href):

[weisJ]

It is more likely that I find time to implement feDropShadow. feImage isn't implemented yet due to #70 and layout being rather complicated (preserveAspectRatio makes this messy at the moment).

[weisJ]

feDropShadow is now implemented in the current snapshot.

[stanio]

Verified with current 1.5.1-SNAPSHOT – feDropShadow is supported.