Tim Sweeney
speaker
640 appearances
1 recordings
1 series
first heard Apr 2025
last heard Apr 2025
Tim Sweeney’s voice in public audio — every appearance, attributed to the second.
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And so a lot of Unreal Engine's lighting techniques were based on light mapping. We introduced colored lighting. So you could have colored light sources. Then we realized, oh, since we're doing this and we're doing it on light maps, we can actually do some pretty expensive calculations, hundreds of cycles, since we're only calculating it for every one foot of world space rather than every pixel.
And so we introduced a whole bunch of elaborate lighting effects, like torch flickering and the caustic effects of water bouncing off of a surface and so on, and pulsing lights and blinking lights and everything else, and I created a system for compositing them together. So if you had an arbitrary number of light sources, they could all do that. Then I implemented a shadowing algorithm.
If you cast a ray from a light to a point on a surface and see whether it intersects any other geometry, if it doesn't intersect, then the light hits the object, and if it does intersect, then the light hits something else first, and that pixel on the object should be dark. So I built a real-time version of this, and it ran at about a half a frame a second.
So I was running around at half a frame a second, like shooting out light projectiles and looking at dynamic lighting. It was like, someday computers will be fast enough for this, but not today.
So I made a non-real-time version that pre-calculates all the lighting and realized, oh wait, if you pre-calculated the shadowing in an object, you can still apply the lighting dynamically as long as the light's not moving.
So you could do torch flickering with shadows and figure out all the cases of dynamic and static lighting that were actually practical on a computer at the time and expose them to artists and This was the wonderful thing.
I was just typing in these little features, exposing them to artists, and every day they'd find a dropdown with some more lighting options available to them, and they'd start using them, and they'd do things that I never thought possible. And this was always the coolest thing.
As a programmer building an engine, you might think you know the implications of the feature you're building, but artists are so clever that you always find that you've built the capability of doing vastly more than you ever anticipated as they start to use combinations of features together in concert to do ever more amazing things.
That's right. And it's timeless. What do the Renaissance painters do with paints? And what do the early game artists do with early engines? Everybody's figuring out the capabilities of their medium, and you're seeing a revolution.
Yeah. Well, it's a funny thing. So this graphics hardware company had just started up in Finland, and they released a screenshot of what their GPU was doing, and they showed a scene filled with volumetric fog. So you had a foggy room with some light sources in it. And when that happens in the real world, what you see are glows around the lights as the light brightens the fog around it.
But the brightening of the fog diminishes over time because the fog absorbs some lighting. And so the further you get away from the light, the more the more fall off there is. And, you know, you have a bunch of colored lights overlapping together in a space like that. The effect is just absolutely magical. You know, like being out on a foggy light with street lamps above.
It's something that's surreal and just beautiful. So it's like, oh my God, they figured out how to do real-time volumetric fog. I have to figure it out myself. And so that was another 30-hour coding session. Nice.
But at the core, I realized, OK, what's happening here is we have this lighting function saying that light at a particular point in space is falling off with the inverse square of the light, the distance from the light source. The inverse square is all from Isaac Newton, which applies to lighting.
I had to realize was that the way the fog interacted with the light was that you calculate the view from your eye's position to a point on a surface in the world. It's going through fog and you're accumulating more and more light as a function of the amount of light illuminating the fog at that point in time.
And so, well, you know, I'd studied that in mechanical engineering without even knowing it. That's the line integral. You know, you have an integral over a line of some function. Well, this is exactly what it's for. It's for accumulating values of a function over a continuous space and time. And
You know, I did a bunch of math and realized that, oh wow, the integral, and then I looked in a reference book of all of the integrals, and thankfully people had solved them all, and I realized the integral of this transformed 1 over r squared turns out to be solved by the arctangent of r.
And so, you know, if you calculate some parameters based on the position of the eye and the position of the surface point you're ultimately seeing, then you calculate exactly how much fog you can accumulate from that. Of course, you can't do that per pixel because that's hundreds of cycles of CPU time. And so what we had to do is calculate volumetric fog on...
on something equivalent to a light map but uh calculating fog every square meter in the world um and so you know we had enough performance for that built uh volumetric lighting and gave it to the artists and they started building magically detailed levels with volumetric fog and in real time and then um you know decades later i was talking to one of the engineers who'd worked on that hardware and asked about their volumetric fog and told him how it inspired me to um uh
to figure out how to do it in real time myself. He was like, oh no, we cheated. We just rendered it out of 3D Studio Max. That's awesome.
to getting the best result from his code and having absolutely no attachment to passcode. And some of the legendary things he did, the end result was an absolute breakthrough in real-time computer graphics, weren't his first try. They were like,
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