Streaming huge 3D scenes over internet

Question

I want to stream big scenes made of many objects to clients but need some advice on what approach to take. I know PS4 and Battle.NET stream the games even when 70% of the game is not downloaded yet but they work pretty fast with my 18 Mbps connection.

Anyone can please help me where to start and how to start for streaming big scenes?

Answer 1

A lot of these don't necessarily stream huge scenes per se, if "huge scenes" implies transmitting the lowest-level primitive data (individual points, triangles, unique textures on every single object, etc).

They often stream higher-level data like "maps" with a lot of instanced data. For example, they might not transmit the triangles of a thousand trees in a forest. Instead, they might transmit one unique tree asset which is instanced and just scaled and rotated and positioned differently to form a forest (just a unique transformation matrix per tree instance). The result might be that the entire forest can be transmitted without taking much more memory than a single tree's worth of triangles.

They might have two or more characters meshes which have identical geometry or topology and just unique deformations (point positions) or textures ("skins"), significantly reducing the amount of unique data that has to be sent/stored.

When doing this kind of instancing/tiling stuff, what might otherwise be terabytes worth of unique data may fit into megabytes due to the amount of instanced, non-unique data.

So the first step to doing this typically is to build your own level/map editor, e.g. That level/map editor can often serialize something considerably higher-level and tighter than, say, a Wavefront OBJ file due to the sheer amount of tiled/instanced (shared) data. That high-level data ends up being what you stream.

Second is to build scalable servers, and that's a separate beast. To do that often involves very efficient multithreading at the heart of the OS/kernel to achieve very efficient async I/O. There are some great resources out there on this subject, but it's too broad to cover in one simple answer.

And third might be compression of the data to further reduce the required bandwidth.

A commercial game title might seek all three of these, but probably the first thing to realize is that they're not necessarily streaming unique triangles and texels everywhere -- to stream such low-level data would place tremendous strain on the server, especially given the kind of player load that MMOs are designed to handle. There's a whole lot of instanced data that these games, especially MMOs, often use to significantly cut down on the unique data that actually has to occupy memory and be transmitted separately.

Maps and assets are often designed to carefully reuse existing data as much as possible -- carefully made to have maximum repetition to reduce memory requirements but without looking too blatantly redundant (variation vs. economy). They look "huge" but aren't really from a data standpoint given the sheer amount of repetition of the same data, and considering that they don't redundantly store repetitive data. They're typically very, very economical about it.

As far as streaming goes, a simple way might be to break the world down into 2-dimensional regions (with some overlap to allow a seamless experience so that adjacent regions are being streamed as the player travels around the world) with AABBs around them. Stream the data for the region(s) the player is in and possibly visible within the viewing frustum. It can get a lot more elaborate than this but this might serve as a decent starting point.