In this particular case, the original Spelunky is currently open-source, so I don't think he would mind.
Generally, though, this falls into a sort of grey area, as far as I know (but somebody please correct me if I'm wrong). If the software you're taking it from is copyrighted, patented, etc., I would probably avoid using it. Otherwise, if it's being publicly shown by the author, there's probably no reason to worry about the legality of it.
That said, you'll learn a lot of things if you don't just copy code left and right. I realize that in this case, you wrote it yourself, but also keep that in mind.

It's true - people play the game for minutes at a time. It's a simple time-waster, and that seems to be all most people expect on a iPod/phone. It seems understandable enough.
What really baffles me is that they're supposedly making an Angry Birds movie. I have absolutely no idea what the movie would be about, much less why anybody would sit through an hour or more of it.

That'd be the easiest way to do it. If you want the further planes to eventually just become a solid colour, I would suggest making the sprite that you overlay be a white silhouette of the sprite you want to fade. That way, you can easily change the colour you're fading to by changing its image_blend value.

I ended up switching to MSVC. I got through the initial set up and figuring out a new IDE, and then realized I had spent over a week trying to solve this one thing and I've now entirely forgotten where I was going next with this code. Guess I should have written that down or something.

Looks like I'm going to have to rewrite my parser from scratch using a different library. GCC doesn't seem to like anything even remotely complicated with Boost.Spirit, to the point that cc1plus.exe just crashes halfway through compilation without any error messages. Apparently this is a known problem, but there's no definitive fix, and any potential fixes I've heard of haven't helped. I've been trying to get the code to compile for several days, using all sorts of different versions of MinGW, each failing at the same point in slightly different ways.
I guess I could switch to MSVC, but that means dealing with a while bunch of installation stuff that I don't feel like dealing with, as well as killing cross-compatibility (well, without installing even more stuff).

That said, the enemies do seem to respawn faster than in most roguelikes. You aren't pressured to keep moving, but if you stay in one place, you do get attacked quite frequently. Still, it does let you get away with standing around a lot more than in other roguelikes.

COMODO Firewall has a feature called "Defense+" which works as a sort of resident shield. You could say it wasn't really the firewall part of it that did it, but that's why it confused me - I had unblocked the debugger in my antivirus program, but hadn't realized that my firewall had a component that was blocking it, too. Kind of a stupid mistake, but oh well.

Just spent a day and a half trying to figure out why my debugger was reporting a segfault before main(). I had assumed that it was in a static object somewhere in my engine, and continued removing bits and pieces one at a time to see what was the problem. I got it down to the point that this was the only thing in my project:

Code:

#include <iostream>
int main() {
return 0;
}

That was still giving me a segfault, unless I removed iostream.
Then I discovered, an hour later, that my firewall has, out of the blue, decided to start blocking the debugger.

Really, the most pressing question here is: Where's Amingo?!

I was wondering how you guys managed to make such a complicated game in only three days, haha. Clever.
I really liked the atmosphere of a flaming building that you managed to create. The way that it starts to blur and become more red when there's more fire in the room is a nice touch.

I hadn't noticed the option to do so at first, but you can turn off the upscaling filter in the game's launcher. Makes things look a bit nicer. The GUI elements are still in a different resolution than the rest of the game, though.

Ah, I was mostly responding to moi. Like I said, though, for most people, any graphics at all is a step up from ASCII, and the aim of this game was to make a more accessible roguelike to your average person. Personally, I don't mind the graphics, but I can see where you're coming from.

The graphics are pixel art run through an upscaling filter. Oddly, the walls are just scaled to 2x, as far as I can tell. The menu graphics are higher-resolution than anything else in the game. It's all a bit weird, but you get used to it. It's definitely a step up from ASCII for most people.

Monster zoos are terrifying. I got through one, but there was another one right at the beginning of the next level with some seriously powerful monsters in it.
The vampire skill set is really powerful. I combined that with dual-wielding, shields and melee, so I can hide behind two shields at once while kicking the crap out of anything that comes my way. The mushroom skills are kind of interesting, actually - once you figure out what the mushrooms all do, they're very useful.
Exceptional embarrassment, if you hold shift while you click an item, it automatically puts it in your inventory. I hadn't realized that at first, but it makes it way easier to pick things up.

http://www.weebls-stuff.com/songs/badgers/
It's been around for ages. I'm surprised you've never heard of it. The point AlexMdle was making was that, at a 45 degree angle, his sprite looks like a badger's head, so he transposed the sprite onto the badgers. It made me chuckle, anyway.

Man, Boost has some seriously complicated template magic going on, particularly with Spirit. I can stand the long compile times, but the real problem is that the compiler can't actually tell me where the error is in your code since it's such a huge pile of templates. I spent several hours trying to figure out why my game would fail at the assembler level with cryptic error messages. I still haven't entirely figured out why, but it seems to have something to do with overusing phoenix::at_c within semantic actions, in combination with the permutation operator. I ended up fixing it, but I don't really know why it's been fixed - I shuffled some code into different rules and then combined the rules, and now it compiles and assembles properly.

Yeah, I tend not to show my friends much more than a screenshot or video of the game. When it's a finished, playable product, they're usually a lot more interested.

I'm programming a Spirit2 parser. It's incredibly confusing at first, but I think I'm starting to get it. I'm sure I'm going about it entirely the wrong way, but the parser seems to be working!

People have been (failing at) making "MMO with elements of..." games for years. There's just more of them now. That doesn't change anything, though - the people that make complete and interesting games still exist.

"Drunken Software World Tour".
Hm. Sounds to me like a TIGJam!