Re: Properties of Custom Paint

Hello all,

Custom paint routines have been something I've been thinking about a lot
myself, in the context of SVG.

I haven't yet written all my ideas down, but the general approach would be
based on the web components model.  SVG paint servers are defined with XML
markup fragments, and therefore have corresponding DOM interfaces.  Why not
create a generic <paint> element that could be defined by extending the DOM
interface with a custom paint function that tells the browser what color to
draw at any given point.  Just like web components, the <paint> element
could have child content that defines parameters that would be used by the
interface when building that function.

I bring this up because of course it would be preferable to have a
consistent underlying model for defining the paint, regardless of whether
it was used in CSS or SVG.

SVG custom paint servers may also be the easier first step towards CSS
custom paint servers, mostly because you would not have to hack the CSS
parser.  The CSS declaration for using the paint as SVG fill or stroke
would be a standard url(#myPaint) reference.  A proof-of-concept (if not
very performant) polyfill is feasible, that would replace each usage of the
custom paint server with an SVG <pattern> containing an image copy of the
canvas rendered by the painting function.

With respect to the specific requirements outlined on the gist (
https://gist.github.com/bfgeek/758b54a1cab65dff9d69), I think they can all
be equally applicable to the SVG model.  Paint would be dependent on any
layout and style changes to the painted object, but would not affect layout
or other styles.

The last point in the "required" list, regarding geometry data, becomes
very important when talking about painting SVG shapes.  One of the main
limitations of existing SVG paint is that it always applies to a
rectangular region, creating a sheet of wallpaper that is then clipped to
the shape. To create a pattern that follows the shape's contours--even for
something as simple as having a gradient that follows the direction of a
straight line--you need to manually define a matched pair of paint server
and shape with the same coordinates hard-coded.

I'd be happy to bounce around more ideas to figure out how this might
work.  If there is agreement that an SVG Custom Paint Servers Module would
be a good first step for testing out custom paint in general, I can bring
it up in the SVG WG to see if there is support there.

Best,

Amelia Bellamy-Royds