GSoC: Libreoffice Theme (application crashes when I modify ColorConfig on startup)

[Sahil Gautam]

Hi
went through the design of data flow this week. I found myself running away from the VCL
and it's colors, or rather from the question of "how to get 2 way exchange of colors working".

https://gerrit.libreoffice.org/c/core/+/168016  Here's the patch [WIP]

There is quite some information to keep in the head, I would try to briefly describe it.

- So we get colors out of the widget toolkits using the updateSettings() functions.
- We have ColorConfig() which gives access to the ExpertConfiguration colors (or colors in the registry).
- We cannot access ColorConfig inside updateSettings() functions in the VCL (because vcl can't depend on svt).

My plan was to (and still is) to load the registry colors in the StyleSettings object when ColorConfig is
created (in the constructor), and mark a flag in the StyleSettings that the Theme is Loaded.
Note that I want to keep the ThemeColors object and the bLoaded flag as static in the StyleSettings.
The reasons are:

a) this feels right, as the ThemeColors are object independent and depend only on the ExpertConfiguration.
b) this way, I evade the various SetStyleSettings() calls. Otherwise, at the end, there would be some
    call which overwrites the ThemeColors.

So for a user using some custom theme, it the flow goes this way:
- When the ColorConfig is created, the colors are loaded into the static ThemeColors object in StyleSettings,
   and a flag is marked (theme colors loaded)
- Then in each VCLPLUGIN's updateSettings(AllSettings&), we overwrite the colors from the toolkit, and put
   them into the AllSettings object passed as argument. So the theme colors from the registry went to all
   the parts which will be using the StyleSettings.Get...Color() functions.
- Then I have to add some code, which will send back those colors to the toolkit[PENDING].
Seems to work fine.

But the issue comes when the user is using the default theme.
Where would I fill the registry entries from? If I hardcode some values for Automatic scheme,
then what's the point of reading system colors. So I thought what if I mark a flag in the StyleSettings
(not static) when I have read the colors from the toolkit once, and then I will check for that flag
in the ColorConfig constructor. Along with this I added a registry flag for if the SystemColors
are loaded into the ExpertConfiguration or not.

The idea is to load the system colors into the registry for theme colors (for automatic scheme)
once, when the application is started for the first time. then I set that registry setting as colors
are loaded, no need to load when the application starts again. This way the user's preferences for the
Automatic scheme won't be overwritten. **The application is crashing on startup when I tried this**.

TL;DR version

Custom theme:
	Defaults come from the theme, and after that StyleSettings keeps an updated
  	copy of the registry, which is used for the to-and-fro of colors.

Default System Theme:
	System Colors are loaded from the StyleSettings into the registry
	on the first startup, then after that an updated copy of the registry
  	in the StyleSettings is used for the to-and-fro...(same as above)

Problem: When the ColorConfig() constructor is called first, I try to write the colors into the
	 registry (via ColorConfig_Impl), but some listeners fire up, and the application crashes.

If you know of any other approach to get a 2 way color communication between the registry and the
VCLs, then please share. I thought of using the UNO api to access the registry values (seems possible),
but then what's the point of having ColorConfig, I thought.

Regards
Sahil Gautam
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