Aug 10

Bugsmashers: Episode 30

Bugsmashers is here! Find out what Mark Abent has in store for us today.

 

Full Transcript

Mark Abent (MA): Hey everyone, welcome back to Bugsmashers, but before we begin I’ve got a small riddle for you. If I fix a bug, but there was no Jira for the bug, did the bug even exist?

Hey everyone, we’re here in another fancy dancy test level and we have a fun bug where if we’re in the buggy on normal plane, everything is fine, but as soon as we have gravity that’s not aligned to the standard world Z, you know Z down, we get some fun issues with the view. So let’s take a look at that.

Weee. So if I pop in third person, oh no! All the shenanigans. This buggy code was written with the assumption that the world Z was always pointing down, but if you have you know let’s see, we have something like I have here where I have a gravity box pointing 45 degrees to the side and not world Z down, the code just goes bonkers because it makes assumptions that it shouldn’t be making.

So let’s pop out, turn our free cam off. Alright. So hop into our legacy buggy code. This particular view or this vehicle seat view is for the buggy, or basically any what do you call it, driving vehicles and what it does is as you’re driving… I can show you. Weee, hop in. So as you’re driving, it kind of wants to keep the view towards, well no I flew off. I have to increase gravity, this shenanigans. Game design, always something. There we go, increased our bounding box. Hop in, there we go. Alright back to the buggy. What this views tries to do is as you’re moving, it tries to center the view behind you or towards where roughly the velocity is so, if you’re moving this way, it tries to rotate you behind and if I back up, it will try to you know, go behind my buggy. It’s mostly so that you can see roughly where you’re driving towards. If it always behind you or in one particular view, you could hit a wall and not know why so it’s a pretty nice fun thing, and of course you can move around, but then if you let go of the mouse it will try to orientate itself, and because it’s assuming that fun Z down issue, we get all sorts of alignment stuff when we have gravity that’s not on the same alignment as the world. Especially for planets where you’re going to have a sphere and the gravity’s always going to be relative to the planet so we can’t always assume the world Z is down.

So we had Chad Zamzow create a nifty little fix where if I uncomment this, he basically has this thing called a gravity rotation, and its matrix he’s using to figure out if all the code here before assume that Z down, so if we’re going to assume that all the codes going to stay like that, but we’re going to have a rotation, this grav rot basically says: “Alright, we assume this is all Z down, but we’re going to move it this way”. This is what this little grav rotation gives us. So it’s like “Alright, we can keep the code that everything’s down, but we’re going to assume that we can modify our gravity”,  So this guy says what our opposite says. So what we can do if we traced all the areas that use this new thing, we can get our velocity and then check to see what our rotations going to be and use that to determine you know, we’re flying along the axis and do all sorts of fun little updates.

So he transforms the velocity, the angular momentum, and if we pop down… Where is it. In here, the second thing he finally does is,  it’s at the very end but we shoot a ray trace. Given that we have transformed, use my fun little car. So if the Z’s pointing this way, and then we rotate it this way, we apply the offset to the whole view and we even apply it to when we shoot trace lines so that if you’re against the wall, it will bump into the correct location and rotate according to that gravity bounds.

So if we pop back in with his fun fix. Recode! What’s cool is since he’s using the gravity straight from physics, this will work if you’re in a buggy that’s driving inside of a constellation or a bigger ship. If you’re on a planet, if you have gravity box it will work depending upon what our fun gravity is.

Back to our non world Z gravity. Hop back in, weeee. Turn on our car, go to the third person and wala! As we move around, he applies the offset so everything works just as expected and the code assumes everything was Z down, but because he’s now applying that offset, everything gets lined up correctly. The position, the rotation and even the speed. So as you’re zooming by, the camera will pan towards your velocity and if you back up, it will go the opposite way. Of course it’s limited by parameters by the designers, but it works as expected. The beauty of this is if you’re on a planet and if you’re going around and around, it aligns up perfect with the gravity. So as you go around, the camera is stuck to the vehicle as it should.

Well, hope you guys enjoyed, I’ll fly off into outer space, weeee.

So the buggy had some buggy code where it assumed that the gravity was always pointing Z down so if you rotated, the gravity still faces this way instead of down, the camera just goes ballistic because it’s still assuming it’s down and good old Chad had a little nifty fix where he figured out what the actual gravity was, so even though it assumed this way for the code, we could find the offset and then apply the offset to the velocity, the angular velocity, basically everything that was needed that the camera assumes and rotates around and he just applied the offset to it, worked like a charm, the buggy is no longer buggy, and that’s never going to get old, and now everything works as expected. You can drive around the planet or even weird crazy gravity vectors and the camera stays behind like it should. Hope you guys enjoyed, until the next buggy bug.

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