2019-06-07-terminal-palette.txt

          Modern look for the graphical terminal

Some weeks ago, I was finally done with the wishy-washy
[https://en.wikipedia.org/wiki/Solarized_(color_scheme)#Gallery - Solarized Dark]
color theme in my terminals and searched for a palette rich of
contrast but still pleasing to the eyes. The new color palette inspired me
to a small coding project for our graphical terminal over the
Hack'n'Hike weekend.

I went for the
[http://chriskempson.com/projects/base16/ - Base16 Classic Dark]
color palette by Chris Kempson.

[image vim_syntax] ViM syntax highlighting with the old (left) and the
  new palette (right)

Before adding my color values to the terminal I had to dive into the existing
[https://github.com/genodelabs/genode/tree/master/repos/gems/src/server/terminal - implementation].
The Genode terminal component provides the Terminal
service and uses a Nitpicker GUI session for screen representation. It uses the
[https://github.com/genodelabs/genode/tree/master/repos/gems/src/lib/vfs/ttf - vfs_ttf]
VFS plugin for font rendering and the color handling is encapsulated
in 'class Terminal::Color_palette'. Any palette has 16 colors with
index 0-7 for normal representation and index 8-15 for bright/bold
colors. The existing implementation also had an undocumented feature to
tweak colors by configuration for the Sculpt Leitzentrale.

I reworked the config mechanism and made it an explicit documented
feature, which is also used on component instantiation to setup the
default palette to Base16 Classic Dark. While coding I also discovered
that the handling of foreground and background color values did not
fit the new palette nicely and revised the approach. Now, requests for
foreground color indices to the palette return the original color
value while background colors get reduced intensity by calculating 75 %
values of the RGB color channels. Last but not least, I replaced the
existing implementation of the inverse/reverse attribute by an
approach that just swaps the color indices for foreground and
background before requesting colors from the palette.

[image vim_hi] The new palette ensures readability of all ViM
  highlighting patterns

For experimentation with the new terminal palette, you may adapt the
default colors in Sculpt's Leitzentrale by copying
_/config/managed/fonts_ to _/config/fonts_ and editing the palette
entry at the bottom like follows.

!<config>
!  ...
!  <palette>
!    <color index="0" value="#000000"/> <!-- black is real black -->
!    <color index="8" value="#105010"/> <!-- bright black stands out a bit green -->
!  </palette>
!</config>

The patch already entered out staging branch and will be available in
master after the current QA cycle.

| sculpt