I'll add my "two cents". To be frank, I did not yet have chance to explore Allegro 5 and learn how much is different from A4 (code-wise). But the general issue is that allegro 4 calls are scattered throughout the engine (those that deal with graphics and controls mainly) instead of being groupped (like in helper functions or classes). If it is only about changing function names, it is not much of a problem. But I fear that there may be changes to logic of usage, in such case certain parts of AGS should be completely overwritten.
As I see it (just a basic idea) there is fast way and "good" way. Fast way is just discard all code style considerations and brute-force Allegro 5 into engine. "Good way" is to properly reorganize the code, hide Allegro 4 calls under interfaces, like Bitmap, Graphics, Mouse etc classes, only then port to A5. I like second way more, but I have no idea how much more time it will take. Depends on how many people involved, I guess. Maybe hacking A5 in place of A4 won't make AGS code too much worse, than it is
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EDIT: Couple things more:
- The editor uses Allegro 4 too, for converting graphics. I guess (only guess) that is minor issue and could be fixed more easier.
- I really hope there's compatibility between A4 and A5 resources (like bitmaps structure). Otherwise there must be a conversion.
