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Dirty Coding Tricks

August 20, 2009 Article Start Previous Page 2 of 4 Next

10-Tative Code

Back at [company X], I think it was near the end of [the project], we had an object in one of the levels that needed to be hidden. We didn't want to re-export the level and we did not use checksum names. So right smack in the middle of the engine code we had something like the following. The game shipped with this in.

if( level == 10 && object == 56 )

Maybe a year later, an artist using our engine came to us very frustrated about why an object in their level was not showing up after exporting to what resolved to level 10. I wonder why?

- Anonymous

All Signs Point to "No-No"

This issue came up during Raven Software's new Wolfenstein, as I was setting up controller support for the 360. It turned out that for the Live integration, we had to know which controller was sending input events. The Doom 3 input code we were using was derived almost straight from Quake 3, so it was a pretty simple system.

In the existing event system, each event was passed around with two integer arguments and a void pointer in case you needed extra parameters. So the goal was to associate a controller ID with each input event. No problem -- just pack the controller ID into one of the event's integer arguments, right? Of course, they were both already in use.

Then came the next idea: Let's just use our fast no-fragmentation per-frame allocator to reserve some memory, plop the controller id in there, and then pass a pointer to it in the event's pointer slot.

It turns out that the event system would take it upon itself to free() the event's void pointer after processing the event. Of course this was totally incompatible with the multiheap approach that we were using. Moreover, there were a few legacy Doom 3 chunks that actually relied on the event code calling free(), so we couldn't just remove the call without non-trivial changes across the codebase. What about adding a third integer parameter? Well, that would involve changing several hundred function calls.

The deadline is looming, I can't spend much more time on this. So, I did the unthinkable -- I packed the controller id into the pointer parameter. I marked it as a horrible hack in a 4-line all-caps comment, and checked it in. This worked fine for a while, and lasted until the whole input system was replaced with something a little better down the line.

- David Dynerman

Velcro Sneaks

Here's a tale from a project in the early PS2 days. We had a ton of collision/bounding issues that were largely solved at the last minute by a rewrite of character collision to use a "collider" model -- a stack of spheres that were way better at resolving bumps vs. boxes than our hierarchical tree of oriented boxes ever could be (ah, the Land Before Havok).

However, we had a rare bug for ages that was pretty maddening -- we called it Velcro-ing -- where every now and then the player character would be up against a wall and sliding along it, but then a sphere of the collider would suddenly decide it was on the wrong side of the wall and wouldn't let you get away from it (i.e. you'd be stuck to the wall's surface).

This was one of those god-awful "sounds easy" bugs -- just figure out why the sphere thinks it's on the wrong side, and fix it. Problem is, you had to catch what happened in all the collision resolutions before it happened to figure this one out.

When you'd drop in things like handy conditional breakpoints to look for a weird response, or a push that made it get confused where it was on a skinny box or something similar, it'd bog the frame rate down and the issue simply wouldn't happen. (The real fix to this problem took blood, sweat, tears, and I think other fluids not usually required, but that is another story.)

Since we were trying to submit, and regularly would get this issue as a blocking bug, one "solution" was to buff out the bounding on whatever was causing the problem, which was guaranteed to make it not happen, but was clearly not the right fix. We'd forward the bug to our art team, they'd fix up that case, and in the ensuing turn-around time, we bought ourselves precious days to keep trying to track down the actual deep, subtle problem.

Testers would typically send back a "player hit invisible wall, player must not hit invisible wall" bug of roughly equal severity (bounding the wall tightly again fixed that, as Velcro-ing was really rare and hard to reproduce anyway), but after a couple cycles of this as we cleaned up the rest of the game, the blood, sweat, and tears fix was eventually found and off we went to duplication and shelves.

This wasn't the proudest cycle of bug-turn-around-stalling, but it got the upper-ups off our backs, because we could say "oh, no, we released that to testing yesterday," and keep scrambling to figure out that damned flipping issue.

- Anonymous

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