T w e n t y S i d e d
The most central problem to rendering any wide open space is, “How do we avoid drawing everything in the entire world?” You can see this problem at work in open world games like Grand Theft Auto. You’re navigating around a massive city. There are literally tens of thousands (maybe even hundreds of thousands) of objects around the city: Street lights, dumpsters, trash cans, newspaper stands, benches, trees, mailboxes, awnings, telephone poles, parking meters, street signs, traffic cones, trash bags, chain-link fences, and jersey barriers.
And crates. Can’t forget the crates.
I don’t care how much horsepower you have, how much memory you’ve got, or how many surfboard-sized graphics cards you glue together and jam inside your PC: Taking all of that clutter for the entire city and hurling it at the graphics hardware would be ruinous.
So the game needs some way of controlling what things get drawn and how detailed they are. The trash cans two miles away? They don’t even need to be in memory. The street lamp four blocks away? That gets drawn, but we’re going to draw a crude simplified version of it, probably a simple vertical beam with four sides. At this distance it doesn’t matter how crappy it looks, we just need a little black pole to stand in for the real thing. But this mailbox right beside the camera? That needs to be rendered in full detail.
The process of sorting this out is called Level Of Detail. It’s a complicated and interesting branch of knowledge. The trick is that the optimal LOD solution will vary a great deal based on your project. The system used by Grand Theft Auto IV is going to be very different from the one in Spore, which is again different from the one in World of Warcraft. Or Far Cry. Or Minecraft.
The thing is, in the vast majority of cases LOD is something that gets sorted out by the CPU. In my very first programming project here on the site, I spent the entire time sorting through polygons and topography, figuring out what parts were worth drawing and what parts could be simplified. But we live in a strange world now.
You know what we need? A Terrible Car Analogy:
Continue reading ⟩⟩ “Frontier Rebooted Part 5: Kneel Before LOD”
