[Freeciv-Dev] Tidying savegames to pave the way for plug mapgens

[Cameron Morland <cameron@xxxxxxxxxx>]

Hi,

This patch does a number of things, primarily to make plug-in map
generators much easier to write. For the most part I've been changing
what is required to successfully load a file as a savegame.

While I was at it I removed some features required to load extremely
old savegames. We already require that a savegame claim to be version
1.9.0 or later, so checking for features from 1.1 (!) isn't
productive.

Irrelevant Parameters
=====================
First of all, there are a very large number of parameters in a
savegame file, many of which do not need to be stored in the game,
especially for scenarios. It should be possible to set parameters,
such as gold, skill_level, nplayers, settlers, explorers, save_nturns,
etc and then load a scenario, without the scenario overriding the
specified values.

Most `x = secfile_lookup_<type>(...)` statements have been replaced
with `x = secfile_lookup_<type>_default(..., x)`, ie use the value
which the person running the server has already specified (or the
default, if the user hasn't specified anything). Most options just
need to be recorded in the file if the file wishes to change 
the pre-existing value. For more complex options, such as
fixed_start_positions and heightmaps (see below), I use the
has_capability thing, so the savegame must specify that it will use
those features. 

The only parameters that a scenario must specify are map.width,
map.height, game.version >= 10900, and game.server_state == 0.
If a scenario wants to keep its tinyisles, it has to specify
tinyisles=1; mapgen makes much more sense this way.

Loading Height Maps
===================
Currently, generators{1,5} construct a height map, then run make_land to
add the terrains. Generators{2,3,4} make tilemaps directly, including
rivers. I wanted external generators to be able to make use of the
terrain/river/specials placing algorithms (especially since Karen and
Ross have been working on making them better), so they needed to be
able to provide height maps.

With this patch, a map can provide a height map, which is a 16-bit
hexadecimal map. Once this is loaded the built-in terrain placing
algorithm runs (with specified landmass, etc), and a tilemap is
created. 

General mapgen layout
=====================
A few bits of mapgen make more sense now (IMHO). Instead of requiring
each generator to do everything, it can specify what it does by
setting booleans, then default functions can be applied later. This
should make the code tidier. 

Since making rivers depends on having a height map, I wrote a simple
function to generate a heightmap given a tilemap.

Load Command
============
If you ask for help on the 'load' command, it will say that "Any
current data including players, rulesets and server options are lost."
This is rather annoying, and is mostly fixed by the "irrelevant
parameters" section above. It still screws up the players, but pretty
well everything else should be left alone (assuming, of course, that
the file you load doesn't specify these things). It's a start.

External Generators
===================
I haven't written the glue code to run external map generators, I've
just been running them from the command line, redirecting to a file,
then loading the file. But now at least the plug-in generators don't
have to be so complicated; if they want to use a heightmap technique,
they can just generate the heightmap and let mapgen do the rest.

Attached are the diff, and a pretty terrible map generator written in
Perl (it's not a great generator, it's just something I hacked
together as an example). Comments? I'll be away for a few days, but
I'd like to see what people think.

incompletemaps.diff
Description: Text document

punchmap.pl
Description: Perl program