This is a patch to adds 3 other OT-SVG hooks to FreeType2-demos. There is an extension on top of it, to

add COLRv1 rendering, too.

The COLRv1 extension currently has a limitation - it works by over-writing

the SVG rendering with a toggle key, so it depends on the font having a SVG table. In one without, it overwrites

the glyh rendering and does gray. (Hope to fix). So it is convenient that both Rsvg and Adobe SVG rendering are flawed.

[Adobe SVG Native](https://github.com/adobe/svg-native-viewer/issues/185) , and [Rsvg issue](https://gitlab.gnome.org/GNOME/librsvg/-/issues/997).

It is a toggle-key to toggle SVG<->COLRv1 rendering ("z" for "color layered glyphs" as for COLRv0),

and overloads the palette toggle key ("C" for switching palettes for color-blind-friendiness in glyf mode)

to switch CPAL entries. Binaries at the [FontVal binary archive](https://github.com/FontVal-extras/binary-archive/) ).

Skia COLRv1:


The glyf data:


Skia COLRv1 to Alpha channel:


Skia COLRv1 to Gray:


Skia COLRv1:


Skia SVG:


Difficult to tell the difference by the naked eye. Here is the programmatic highlights (with ImageMagick's `compare`):


index 0:


index 1:


index 2:


index 3:


index 4:


index 5:


index 6: