[Freeciv-Dev] switching tilesets at runtime

[Jason Short <vze2zq63@xxxxxxxxxxx>]

Here's a preliminary (buggy and incomplete) patch to allow switching 
tilesets at runtime.
It implements a new function, tilespec_reread, in tilespec.[ch].  When 
invoked this function should destroy the old tileset data and load the 
given new tileset.
This is explained in more detail in the patch, but the details are 
pretty tricky.  Loading a tileset consists of three parts:
1.  The top level tileset data is read from the specfile.
2.  All images are loaded and placed into a hash.
3.  When we receive ruleset data from the server, the sprite structure 
is initialized to setup that sprite to point to the appropriate picture.
Step #3 is pretty difficult to mimic.  I basically iterate over all 
valid ID's for each element and setup the sprite for that ID.  Hopefully 
(and this seems to work) if the ID is invalid the sprite will just be 
initialized to NULL (and won't be used anyway).

That said, there are three bugs that I know of:

1.  Rampant memory leaks.  Fixing these will probably require writing a 
new function to free the images.  However, the memory leaks as they are 
don't seem to make the system unusable - memory use doesn't grow 
linearly; it gives the appearance that each tileset is cached by the 
loader so switching repeatedly doesn't result in quickly unbounded 
memory growth.
2.  The city dialog view is not properly resized in GTK.  This is a 
GUI-specific issue, so it's probably best to create a new gui-specific 
function to be called at the end of the reload.
3.  The mapview is offcenter after the conversion, because 
map_view_x0/map_view_y0 remain the same while the tile size and 
orientation may change.  This is easily fixed.

I've also added some demo code to gui-gtk: an extra item in the "view" 
menu to toggle between trident, engels, and hires tilesets.  Once the 
tileset switching becomes more mature GUI programmers will no doubt want 
to write frontends for tileset selection.
jason