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In principle WebGL should be competitive with OpenGL. Once it hits the GPU, it's the same. Some of the bottlenecks in WebGL are: - Javascript. Modern JS engin

In principle WebGL should be competitive with OpenGL. Once it hits the GPU, it's the same. Some of the bottlenecks in WebGL are: - Javascript. Modern JS engines are great, so the overall speed can be good, but you're still missing things like 64-bit ints, SIMD and threads. (Do game engines make heavy use of threads though? I don't know, but many influential games programmers seem to be wary of them!) - The WebGL -> OpenGL translation layer takes some time. In Chrome it sanity checks your input (which you definitely want in a browser! GPU drivers are very insecure) and executes it in a separate process. Not as expensive as you might think, especially if you minimize your draw calls, which is good practice anyway. - WebGL is basically OpenGL ES 2.0 (and WebGL 2 is ES 3.0), which is missing some useful features of full OpenGL, and doesn't offer the low-level, low-overhead access of Vulkan or Metal. Depending on what you're doing, I'd guess WebGL might be no more than 2x slower (assuming plenty of optimization work). Some fiddly things might be 10x slower, or just not possible at all within the WebGL API. WebGL 2 has a lot of very important new features, but support for that still seems to be patchy, and it's only just catching up with mainstream mobile graphics. It's a generation behind Vulkan. Apart from that, an AAA game will have massive amounts of graphical and audio assets. Delivering that over the network is a pain and HTML5 caching is a pain. Doable, but hardly comparable to just loading it from local storage. Oh, and one more thing! A big game wants sound as well as graphics, and WebAudio is a mess. And audio mixing is typically done in a background thread, so that's one area where the lack of threads in JS is a real problem. Overall WebGL is very nice, it was a great choice to follow OpenGL ES closely (security problems aside).

sho_hn 9y ago
> Do game engines make heavy use of threads though? Boy do they, yes.
- iainmerrick 9y ago
  Can you go into more detail? (Or point me at some up-to-date books or blog posts!) I'm specifically curious about CPU-intensive stuff that is sharded out to multiple threads. That's your classic multithreaded programming, the sort of thing you'd do in scientific computing, but I always got the impression games people were skeptical about it, due to unpredictable performance and the high risk of bugs.
  - wlesieutre 9y ago
    Not an expert, but the version of it that I've heard is your main game loop handles all interaction with the game state to avoid issues. You can offload rendering into another thread pretty safely, and anything that alters game state would queue up its state changes for batch processing. That way if you're running a multithreaded physics simulation you can get two separate bullet collision detections on one object, and instead of trying to delete the object twice you put both "kill this thing" actions on a to-do list. When it comes time to handle that in the main loop, you sweep through it for conflicts before executing any of the changes. UE4 in particular I know handles all game logic in a single thread, and you can't touch UObjects from outside of that. But here's an example (without much technical detail) of someone implementing multithreaded pathfinding for UE4: https://forums.unrealengine.com/community/work-in-progress/11929-rama-s-multi-threaded-dynamic-pathing-system-full-physics-support https://forums.unrealengine.com/community/work-in-progress/1...
    - iainmerrick 9y ago
      UE4 in particular I know handles all game logic in a single thread, and you can't touch UObjects from outside of that. Yeah, that's the kind of thing I was thinking of when I said games programmers seemed skeptical of threads. Some of that coarse-grained parallelism could possibly be done in JS with Web Workers, but those have their own problems. (See the recent discussion here about the "tasklets" proposal: https://news.ycombinator.com/item?id=15511519 https://news.ycombinator.com/item?id=15511519)
  - corysama 9y ago
    Motivation: The Xbox360 pretty much forced gamedevs into heavy threading if they wanted to get anything done. It had 3 PowerPC cores with 2 hardware threads each. The cores had huge memory latency and no out-of-order execution. IBM's attitude about OOE was "Statically compile for a fixed target" and "Run 2 threads per core and that that'll cut the effective stall cycles per thread in half". The PS3 had only 1 of those PC cores, but it also had 6 unique cores that were practically high-power DSPs. If you manually pipelined data movement and vectorized execution, you could get amazing results. If you ignored those cores, the PS3 was crippled. The XBone and PS4 have friendlier cores, but they are still surprisingly low-power and there are 8 of them. So, you still need to thread and vectorize or you'll be dragging. Even on the PC, Sutter's "The Free Lunch is Over" is over 12 years old. Outside of games, the browsers force single-threading and cloud servers profit by selling multicore machines pretending to be many single-core machines. But, in games have to run on non-virtual hardware. Execution: You can google around for "game engine job system", but unfortunately, game engine blogs have really fallen off a while back as most of that crew has moved to twitter. So, the best material out there is in the form of GDC presentations such as "Parallelizing the Naughty Dog engine using fibers", " Destiny's Multithreaded Rendering Architecture", "Multithreading the Entire Destiny Engine", "Killzone Shadow Fall: Threading the Entity Update on PS4". Slides and videos are available around the web.

sho_hn 9y ago

> Do game engines make heavy use of threads though? Boy do they, yes.

iainmerrick 9y ago
Can you go into more detail? (Or point me at some up-to-date books or blog posts!) I'm specifically curious about CPU-intensive stuff that is sharded out to multiple threads. That's your classic multithreaded programming, the sort of thing you'd do in scientific computing, but I always got the impression games people were skeptical about it, due to unpredictable performance and the high risk of bugs.
- wlesieutre 9y ago
  Not an expert, but the version of it that I've heard is your main game loop handles all interaction with the game state to avoid issues. You can offload rendering into another thread pretty safely, and anything that alters game state would queue up its state changes for batch processing. That way if you're running a multithreaded physics simulation you can get two separate bullet collision detections on one object, and instead of trying to delete the object twice you put both "kill this thing" actions on a to-do list. When it comes time to handle that in the main loop, you sweep through it for conflicts before executing any of the changes. UE4 in particular I know handles all game logic in a single thread, and you can't touch UObjects from outside of that. But here's an example (without much technical detail) of someone implementing multithreaded pathfinding for UE4: https://forums.unrealengine.com/community/work-in-progress/11929-rama-s-multi-threaded-dynamic-pathing-system-full-physics-support https://forums.unrealengine.com/community/work-in-progress/1...
  - iainmerrick 9y ago
    UE4 in particular I know handles all game logic in a single thread, and you can't touch UObjects from outside of that. Yeah, that's the kind of thing I was thinking of when I said games programmers seemed skeptical of threads. Some of that coarse-grained parallelism could possibly be done in JS with Web Workers, but those have their own problems. (See the recent discussion here about the "tasklets" proposal: https://news.ycombinator.com/item?id=15511519 https://news.ycombinator.com/item?id=15511519)
- corysama 9y ago
  Motivation: The Xbox360 pretty much forced gamedevs into heavy threading if they wanted to get anything done. It had 3 PowerPC cores with 2 hardware threads each. The cores had huge memory latency and no out-of-order execution. IBM's attitude about OOE was "Statically compile for a fixed target" and "Run 2 threads per core and that that'll cut the effective stall cycles per thread in half". The PS3 had only 1 of those PC cores, but it also had 6 unique cores that were practically high-power DSPs. If you manually pipelined data movement and vectorized execution, you could get amazing results. If you ignored those cores, the PS3 was crippled. The XBone and PS4 have friendlier cores, but they are still surprisingly low-power and there are 8 of them. So, you still need to thread and vectorize or you'll be dragging. Even on the PC, Sutter's "The Free Lunch is Over" is over 12 years old. Outside of games, the browsers force single-threading and cloud servers profit by selling multicore machines pretending to be many single-core machines. But, in games have to run on non-virtual hardware. Execution: You can google around for "game engine job system", but unfortunately, game engine blogs have really fallen off a while back as most of that crew has moved to twitter. So, the best material out there is in the form of GDC presentations such as "Parallelizing the Naughty Dog engine using fibers", " Destiny's Multithreaded Rendering Architecture", "Multithreading the Entire Destiny Engine", "Killzone Shadow Fall: Threading the Entity Update on PS4". Slides and videos are available around the web.