[fpc-pascal] Converting a graphical DOS program to fpc

[Simon Webster]

Dear Free Pascallers,

I'm wanting to convert a Turbo Pascal program to fpc, to run
(ultimately) under linux, although I'm actually developing on a mac,
and using virtualbox to run ubuntu. The program in question is a
relatively large non OOP program which makes substantial use of BGI
graphics. I'm wondering what would be the best/easiest way of
achieving this?

I tried using the graph unit & svgalib under a virtualized ubuntu, but
even the simplest test program (InitGraph, putpixel, CloseGraph)
produces a runtime error 216. Even if I got this working, I get the
feeling that directly bashing the graphics hardware in such a
primitive way is not the best way to go.

Ideally I would like to be able to just open a large window that I can
use as a bitmap for all my graphics drawing, ideally using graph unit
syntax compatible functions. What's the simplest way to do this - I
tried looking in the documentation but don't really know where to
start. Do I need to use 'Lazarus' if I want to open a window? I've no
experience with Delphi or Object Pascal so that whole aspect of fpc is
completely alien to me.

Many thanks in advance for any help,
Simon