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Showing posts from August, 2008

Typo and my bool

Notice a problem with this?
if (abs(bullet.xSpeed > 0)) {

It took me a good 10 minutes to find that problem. Alas, I must have added that typo when I was moving some of my utility functions (min, max, abs) to a more logical home. Ah well.

I also got into trouble last night with bools. Fore some reason, most of the controls for the game worked, but L and R would not. Turns out it has to do with switching from my own typedef'd bool, which was just typedef'd from an integer, to using libnds's bool, which is enum'd as true and false (for those of you used to fancy-schmancy modern languages, C doesn't have a built-in bool, (well, sortof. C99 does, but we won't go there)). I was trying to return a bool value of 512, which using my old method, would evaluate as true. Using libnds's method, it's probably undefined behavior (I'm not sure what the C spec says about doing this), but definitely didn't work. But the fact that it worked for a bunch of…

On a roll

Wow, I'm getting a lot done this week. Last night, the kids went to bed quickly and easily, and Sara decided to watch the Olympics, giving me a little more than an hour to get stuff done!

I managed to:
Fix the priorities, so sprites appear behind the foreground tiles. This was fairly simple -- I just had the priority numbers wrong. Which makes me wonder how it ever worked in the GBA version, but I didn't get around to comparing the codebases to find out why.Add black foreground borders around small dungeon rooms. Before that, it looked weird when you walked off a could see your character out in the limbo beyond the room as you exited. So now the black space around the outside of rooms is in the foreground. It was a pretty easy fix, as I took a random room tile, and just gave it an all-black palette, to avoid having to add a new tile.Fix a few other minor scrolling glitchesGet the overworld tiles to load correctly. Like the priorities, I was doing this dead w…

Correction and signed/unsigned ints

Well, turns out a few people do read this blog after all! Cearn left a comment on my last post correcting my incorrect understanding of bit-shifts, which if you are interested, you can read for full detail, but the gist is that bit shifting WILL preserve the sign bit if it's declared as a signed integer and not an unsigned integer. So I stand corrected. Thanks Cearn!

Which means, looking back through my code, that the problem resulted less from my willy-nilly bit-shifting, and more from using an unsigned integer in one particular function. (which at the time was reasonable, because my engine never used negative screen positions until now).

I managed to scrape together 30 or 40 minutes this weekend to finish changing all of my screen setup and scrolling functions to be happy with signed numbers, and finished added some special cases to deal with rooms that are smaller than the screen size. And now all the backgrounds seem to be drawing and scrolling correctly! The first major …

More screen size and premature optimization

Donald Knuth was right. Optimizations I had done for the gba are killing me. And it all has to do with screen size.

See, my engine wasn't designed to properly handle rooms that were smaller than the screen. The camera's position in the room is stored by a number that I assumed was always positive, because, being equal to or smaller than the room itself, I never had to go negative, or outside the bounds of the room. But now with the bigger screen, the camera is often outside of the bounds of the room. So I need to handle all these special cases where the rooms are smaller than the screen. Two things need to happen: first, it needs to just work right. Second, smaller rooms should be centered horizontally on the screen, (unlike the picture in my last post, which looks goofy being shoved up to the left), and bottom-aligned with the screen, so there is less overlap between the HUD and the game. So I've got that to do, which I've started on, but is messy.

A big chun…

Screen size

Well, I'm getting closer! As you can see on the right, things look almost normal!

The biggest problem I ran into so far was the difference in size between the DS screen and the GBA screen. I still need to make better use of the full screen real estate (at least to center small rooms like this one), but the bigger problem was in how the graphics engine deals with the screen size.

See, most scrolling tile games on nintendo's handheld use a small tiled background which wraps around as you move. This background is just big enough to have one row and one column of tiles off the screen at a time. So as the screen scrolls, you redraw the off-screen row or off-screen column (or both), and then scroll it onto the screen. A little tricky, but no problem, really.

The problem comes in that the DS screen width is the same size as the default small wrapping background that I had been using. So I suddenly don't have an offscreen column to draw on. The answer, of course, is to make th…

Sprites, DMA, and caching

In the 2nd picture in my last post, you might have noticed the big brown square in the top-right. Strangely enough, that's a sprite that was appearing and disappearing at weird times. What you don't see in a static picture is how weird clones of the main character and enemy sprites would start appearing at semi-random intervals. Yuck.

Well, as usual, it's DS weirdness that I wasn't counting on that caused it. And this is where I launch into technical ramblings that make the eyes of the general public glaze over and start dreaming of Krispy Kremes.

See, the GBA and the DS both have this cool feature called DMA, which basically means they have a piece of hardware that copies memory from one place to another place, quickly (as opposed to the normal methods of loading a chunk of memory into the cpu, then writing it to another place in memory). Well, what I have been doing is setting up all my sprite information for a frame in regular memory, then, between screen update…

Title screen and vram banks

Well, I've got the title screen working:

But it wasn't without a fair amount of pain. The first step was pretty easy: when I copy the tile data from regular memory to video memory (vram), I needed to make sure I was copying enough -- since I'm using different memory copy routines than I did on the gba.

I did that, ran it in my emulator, and it looked great. Till I ran it on the actual DS, and it was just a blank screen. Bleh. I loaded it up in the No$GBA emulator, which is the most accurate emulator out there, (but you have to pay to get access to most normal debugging features, and unfortunately, the author has disappeared, meaning it's impossible to purchase, so I'm out of luck getting a useful debug version!), and it black screened also. Bother.

So I spent a few hours fiddling around with some DS demos and copying code back and forth, trying to figure out where I went wrong. Turns out it's with DS's funky vram banks.

See, on the gba, your vram is vra…

Getting Started

After enough pestering from random folk, and donations of hardware from the wonderful people at Electrobee, I've decided to go ahead and port my Gameboy Advance game Anguna to the Nintendo DS. It should be a fairly straightforward port, as the DS's 2d hardware is remarkably similar to the GBA, but the fact that my wife and I have 5 month old twins really slows things down. So, since the development will be slightly slow, I figured it'd be interesting to keep a record of where I'm at, and what progress I am (or am not) making on it.

For starters, I decided my first tasks should be:
Get the GBA code to build on Linux. I did the GBA version working entirely in Windows, but I've recently switched over to mostly using Linux, so the build framework needed to work in Linux.Clean up the messy/ugly bits. There were plenty of those, and plenty of places where I built in dependencies on gameboy hardware at too high a level. This, I thought, would be the perfect time to fix…