[fpc-pascal] Migrate Delphi XE5 to FPC/Lazarus, any advice?

[Bo Berglund]

I have this big tomographic data interpretation and visualization
program on my hands for maintenance. It was started back in 2002 by
another developer using Delphi7 and the main development was done up
until 2009 using D7, BDS2006 and RAD2007 by the same guy, who then
left.
Later on when I took over maintenance I unicodified it and updated the
GUI using Delphi XE5 back in 2014-15. I also had to patch the GLScene
code to make it work, not much but essential.

Now in view of the way Embarcadero is licensing the development system
I am thinking about moving over to FPC/Lazarus instead. New functions
have been called for and the original developer is able to consult.

So I am looking for advice on what to think about when doing this
migration to FPC.
The project uses an older version of GLScene, which cannot be replaced
by any current version because of the way GLScene obsoleted methods
and properties in the older versions such that I never could make it
work back in 2014, hence the unicode patch of the older version.
Apart from this it only uses standard functions in Delphi as far as I
know. Plus our own components, which we have full control over...

Suggestions, links etc appreciated!


-- 
Bo Berglund
Developer in Sweden