So I recently finished a game and I use Windows but most of the people on this forum use Linux so I would like to know how easy is it to port it to linux? I could create a virtual linux machine easy enough but I don't know how to use anything in linux. Is it as easy as learning the gcc commands to compile the exact same project or would I need to rewrite some parts of the code/edit resources?

It's all allegro, I don't think I used any platform specific code, but I'm pretty newb. If it's possible for anyone to download the source code (http://www.filedropper.com/194zsource) and just check if it compiles alright I'd really appreciate it.

Hmmm, interesting, thank you so much! I wish I knew more about Linux or programming in general that I'd be able to figure out why the transparency doensn't work. Thank you for taking the time to do that!

I edited my post, the problem was due to the sprite bitmaps not being zeroed out with a fill. It's not due to Allegro, I think.

I didn't look at the source, but from beoran's description I'm betting you have something like:

ALLEGRO_BITMAP *b = al_create_bitmap(w, h);
al_set_target_bitmap(b);
al_draw_bitmap_region(b2, sx, sy, sw, sh, dx, dy, 0);
al_convert_mask_to_alpha(b, color);

After you call al_create_bitmap() the bitmap you created has undefined contents. Which means it might be all zeroes, or it might be random garbage (or it might even be a picture of your gf ). So you have to call al_clear_to_color after al_set_target_bitmap. An alternative way to do it (though in this case it just makes it more complicated I think) is to use a blender like this:

...
al_set_target_bitmap(b);
ALLEGRO_STATE state;
al_store_state(&state, ALLEGRO_STATE_BLENDER);
al_set_blender(ALLEGRO_ADD, ALLEGRO_ONE, ALLEGRO_ZERO);
al_draw_bitmap(b2, ...);
al_restore_state(&state);
...

The "ONE, ZERO" blender doesn't skip alpha pixels: it'll copy them directly into the target instead of "drawing" them... in effect it'll be the same as clearing.

I've seen what Beoran described, though I didn't know it was platform specific. Makes sense that an initialized part of the video buffer would have stuff on it - but the effect, a glitchy, inverted copy of my desktop, was pretty cool to look at.

In general though it's always good practice to assign any block of data before you use it. You don't do int i; printf ("%i", i); for a reason, after all, and when you copy a transparent image to a bitmap with an alpha-aware blending mode (the default), you are implicitly copying what was there before during the blend operation, even if the existing data is junk.

(Emphasis mine:)

This. This was what had me pulling out my hair for days, when I was but a youngling, which was three weeks ago. Because int i; i++; works just fine in the global scope.

I really like C, and I'm sure there are architectural reasons for that "gotcha", but jeez. That's the kind of stuff we make fun of PHP over!

The reason local variables aren't automatically initialized to 0 in C is performance. Normally the first thing you do with local variables is store some calculated result in it, so letting the compiler put a 0 or such in there is a waste of time. And this matters a lot for functions that get called in tight loops.

Global variables do get initialized automatically to 0 because the compiler has to allocate space for those at compile time anyway, and initializing those global variables only happens once at start up of the program, so the performance overhead is far smaller.

In most cases, if you wonder why something is so in C, it's normally either due to legacy code compatibility or performance reasons.