Dolphin Progress May and June 2020

https://dolphin-emu.org/blog/2020/07/05/dolphin-progress-report-may-and-june-2020/

by todsacerdoti • 6 years ago

161 48 6 years ago

Am I the only one constantly blown away by how deeply they can hook into games? Not just "we perfectly emulate the original hardware and produce pixel-perfect screens", but "we read the 3D models and can increase resolution and widen the view" - that's crazy! It's totally different than how I usually imagine "emulation".

chungus• 6 years ago

Right? Here's another example I think is really cool:

"Free Look is a longstanding Dolphin feature that allows the user to reposition the camera in a game however they so please, with abilities far far beyond what game cameras can provide. This allows for exploring blocked off areas, advanced game photography, and more. "

Jasper_3• 6 years ago

That's partly because we got tremendously lucky in how the hardware sends data. Unlike some newer GPUs, the hardware has dedicated memory for the Projection and Model-View Matrices, and the vertex pipeline is fixed-function.

Dolphin isn't reading 3D models, they're just tweaking the matrices that the game sends. Increased resolution sort of similar the same -- the game sends the hardware triangles in an abstract model space, which is converted to clip space (where the left of the screen is -1.0 and the right is 1.0). Increasing the resolution just means adjusting the rest of the transform; everything the game sends is in abstract space.

(Yes, I know there's a bit more to it than that, e.g. virtual XFBs, LOD biases, and so forth)

Basically, unlike the PS2, the GameCube is pretty much an ancestor of modern PC GPUs, so its way of doing graphics is very familiar to us, and maps quite well. And this is not an accident! ATI bought the company that made the GameCube's GPU (ArtX), and put out a GPU so good (the r300) that NVIDIA nearly went out of business.

Also, fun, I ran into the same "GLES doesn't support glReadPixels for depth" when working on the lens flare code for Wind Waker and Super Mario Galaxy in https://noclip.website. Had to do some dirty tricks to convert it to a color format first.

johnchristopher• 6 years ago

What happened after that ? What turned the wave in favour of nVidia ? I was there (as a player) but I don't have clear memories.

dooglius• 6 years ago

You call it "lucky", but isn't it more likely that it was deliberately designed to be resolution-agnostic?

madaxe_again• 6 years ago

Oh, there are whole other levels of “this was never intended but it is incredible”. Such as DolphinVR. It’s exactly what it sounds like, and stuff like wind waker, f zero, twilight princess is just... really something else with the added dimension. It’s not perfect, but it’s seriously impressive and a really neat way to replay decades old games.

ubercow132• 6 years ago

Wow that looks amazing! F-Zero VR! That's the first thing that has ever made me think I might want a VR headset... but just imagining the experience is making me feel a bit queasy.

edit: just watched a video and I am completely sold

solnyshok• 6 years ago

re-encoding my gczs into rvzs right now. looks like I am going to slash about 10 GB off my 65GB library.

ed25519FUUU• 6 years ago

My problem with these formats is that you can’t load/play any them on a regular wii with any of the homebrew apps. It’s emu only.

zamadatix• 6 years ago

Even if you play primarily on a real Wii it's still more convenient to archive a game in 20 MB and expand it to the exact original 1.36 GB ISO when you want to load it on real hardware.

jepler• 6 years ago

Did you find more info on rvzs? The progress report makes it sound like rvz compresses random data, but that's plainly not true. I'd love to understand what "garbage data" actually is. It must actually have lots of pattern, rather than being random data.

bonzini• 6 years ago

It's data not pointed to by the filesystem. Most of the time it's zeroes, but it could be meaningful data for copy protection or sometimes even source code was found (this last thing IIRC, I might be confusing two different things).

Wowfunhappy• 6 years ago

Does this work? My understanding was that gczs are a lossy compression format, so it seems like going from gcz or rvzs would be hard or at least create an imperfect result.

alvarosevilla955• 6 years ago

Slightly related, a couple of weeks ago a guy named Fizzi released a dolphin build with rollback netcode support for Super Smash Bros Melee, making it a game with better netcode than most current big name fighters.

The way he implemented it is insane, he had to reverse engineer a way to generate arbitrary game states in game, as using dolphin savestates was not performant enough.

He's also added other amazing features, like in game matchmaking, or my favorite, being able to stream a game state through the Wiis ethernet port, so two players can be competing on original hardware while a stream setup upscales that footage in realtime to 16:9 4k through Dolphin, and also generates real time match stats, saves replays... Incredible stuff.

Here's the project page: https://slippi.gg/ and a video from a top melee player showcasing the matchmaking: https://www.youtube.com/watch?v=erbZV8u6-hA

Roritharr• 6 years ago

I always love when technical accomplishments like this show how insanely effective lone people can be when they throw themselves at a task with a heart full of love for the subject.

Commercial environments would have called these ideas unfeasible before the first line of code was written.

saagarjha• 6 years ago

I know a guy who added basically full collaborative support to IDA Pro, doing something similar (IIRC, hooking all state transitions). Some people are just way out there.

akhilcacharya• 6 years ago

That's remarkable. What do these devs do for their day job?

karlding2• 6 years ago

The developer (to be pedantic, there's only one full-time developer, Fizzi, the others are volunteers) quit their day job last year to work on Slippi full-time [0], with funding from Patreon. More details are available on the project site about the other contributors [1].

[0] https://twitter.com/fizzi36/status/1199734629252653057

[1] https://slippi.gg/about

alvarosevilla955• 6 years ago

Fizzi actually left his job at smash.gg on November to focus solely on the rollback project. He has a Patreon [0], and the community has shown quite the support: he gained 1k patreons in the 24h following the release. Another main contributor, UnclePunch, who's written most of the ASM to directly interact with the game, also has some Patreon support. There's also other contributors working on their free time AFAIK.

[0]: I'm not affiliated with Fizzi but I'm not sure if sharing his patreon would be spam, so I'll say you can find it in the project website from my previous comment.

syspec• 6 years ago

Do you have a link to any blog posts, i would love to read about it. I tried to look on http://slippi.gg, but development appears to be closed source?

I'm just an outside observer, but i love the topic. For others like myself, this is a great GDC video to watch on the topic

8 Frames in 16ms: Rollback Networking in Mortal Kombat and Injustice 2

https://www.youtube.com/watch?v=7jb0FOcImdg

karlding2• 6 years ago

I submitted a blog post a few weeks ago about the way they handled game state synchronization in replays [0]. The netplay release is still relatively new, so if there is a blog post in the works, it'll probably be at a later date.

[0] https://news.ycombinator.com/item?id=23643784

alvarosevilla955• 6 years ago

It's not obvious on the website but everything is on Github[0] with different repos for the forked Dolphin build, the desktop app, melee assembly...

As to dev blogs, they have a medium[1] with some interesting posts, but nothing too recent, I hope they'll do one in time with all the new stuff.

On top of the rollback, something very notable they did was realising melee has 3 frames of input lag when running on native hardware, so they managed to remove them from Dolphin when running on 120hz screens. This allowed them to keep those frames as a delay buffer without actually having a real effect on gameplay.[2]

[0] Slippi Github: https://github.com/project-slippi/

[1] Dev Blog: https://medium.com/project-slippi

[2] Post about Faster Melee, the previous netcode iteration, going into the input delays: https://www.reddit.com/r/SSBM/comments/azoiqz/faster_melee_2...

Thaxll• 6 years ago

Super Smash Bros Melee was released in 2008, networking was way different back then + all the good libraries language you have now it's much easier.

alvarosevilla955• 6 years ago

Melee came out in 2001. Neither the game nor it's original console have any networking support.

If you're referring to my comparison, I'm talking about current gen titles. In fact, with this you can now play play cross-country with less input lag than Smash Ultimate offline

Klonoar3• 6 years ago

You're thinking of Brawl, not Melee.

faitswulff• 6 years ago

Is this the same definition for "rollback" netcode? https://en.wikipedia.org/wiki/GGPO#Design

GGPO uses a netcode technique called “rollback”. Rather than waiting for input to be received from other players before simulating the next frame, GGPO predicts the inputs they will send and simulates the next frame without delay using that assumption. When other players’ inputs arrive, if any input didn’t match the prediction, GGPO rolls back the state of the game to the last correct state, then replays all players’ revised inputs back until the current frame. The hope is that the predictions will be correct most of the time, allowing smooth play with minimal sudden changes to the game state.[6][7] The system in itself is highly similar to client-side prediction, but applied to a peer-to-peer setup.

alvarosevilla955• 6 years ago

Yes. This is a custom implementation, not CGPO itself, but the concept is the same.

dahfizz• 6 years ago

Fizzi released a dolphin build with rollback netcode ... making it a game with better netcode than most current big name fighters.

I see this repeated often without justification. Why is rollback better?

Based on my basic understanding, rollback netcode would absolutely fall apart under any suboptimal network conditions. If there's too much lag or packet loss, you and the opponent character will start teleporting all over the screen, missing lots of inputs, etc.

It makes sense that rollback netcode would be preferable when paired with a very good, reliable network (e.g. so if any rollback is needed, it's only a frame or two). But if you're selling a casual game meant for anyone to be able to play, a delay based netcode makes more sense to me. An average Joe can understand "the game is buffering", but if the game starts rolling back too much and you can't control your character because he's teleporting all around, that just looks like a broken game.

An interesting follow up question: if rollback is objectively the better approach, why is it implemented less often? Is it significantly more difficult to develop and does that offset how much value it would add to the game?

Klonoar3• 6 years ago

Rollback more or less massages the differences between players connections. Comparing this to old netplay (Anthers Ladder & co) is night and day differences.

Teleporting rarely happens for me, if ever - and if it does, then I can cancel and move on to the next opponent who generally doesn't exhibit the issue. In a game like Melee, this is huge - you really need to play both to understand how impactful the difference is.

dmonitor• 6 years ago

Rollback is not a replacement for delay-based, but an enhancement to delay. Slippi, for example, still delays the inputs by 2 frames to minimize the inconsistencies that appear. This can (in theory, not sure if it’s implemented in slippi) be increased to any number of frames to reap the benefits that delay based netcode has. Only using delay is objectively inferior because any flaw that rollback has is also shared by delay. You are welcome to try out the old Melee netplay and compare it to the new Slippi to experience this for yourself.

The reason rollback is rarely implemented is because it is hard to motivate a company to do it when the benefits are so intangible. “Better netcode” doesn’t really sell games, flashy graphics does. And since most of the FGC has existed offline, online is just an afterthought.

This video explains fairly well: https://youtu.be/1JHetORRpfQ

tangent128• 6 years ago

If there's "too much" lag or packet loss, delay-based netcode will also become unplayable; the difference is that rollback has more tools to address bad connections, so that rollback is often not even visible:

- predicting that the buttons held down in frame X will be the buttons held down in frame X+1 is actually a pretty good heuristic

- in fighting games, changing directions and attacking generally have windup animations, so if a correction skips a few of the initial animation frames, it still hasn't diverged the overall game state much

- even in bad connections, you still have control of your character; the game doesn't freeze and take you out of the flow (this can be subjective)

- hybrid approaches are possible, where a small fixed delay is used in addition to rollback; short enough to not be obvious to the player, but long enough to avoid rollback in the cases where delay would be sufficient. (delay-based netcode is not good intercontinentally anyways due to the necessary delay for synchronization becoming obvious input lag)

As for why rollback is rarer, yes, it is more difficult; it usually requires a fully deterministic game engine with the ability to snapshot and restore game state, which can be a very intensive retrofit if you didn't design it in from the start.

kupopuffs• 6 years ago

It's a balance between normal delay-input and rollback netcode, not one or the other. You can increase the delay which will reduce teleporting but obviously makes the game more delayed.

Rollback requires your game to be able to rollback to a previous game state. Some games are not developed with this in mind (too much reliance on global state, hard to go backwards in time)

ubercow132• 6 years ago

I don't see why you would think that. On the contrary it is with solely delay-based netcode that the game would miss your inputs, because it will freeze under bad network conditions and anything you input while it is frozen will be missed. Rollback netcode allows the game to keep running and processing your inputs regardless of the network conditions. You might see the other character jump around somewhat but it's unlikely that your character will warp as the game knows all of your inputs. Your own character can basically continue to react perfectly to your input regardless of network conditions.

Klonoar3• 6 years ago

Notably, anybody who's interested in this kind of stuff/if you're looking to hack on a fun project - the issues page is great to scan. The Discord people are generally friendly.

I jumped in and have been poking at some stuff for the macOS build, tons of fun.

reedwolf• 6 years ago

Thought this was going to be about the KDE file explorer, which is an excellent piece of software, btw.

ChrisMarshallNY• 6 years ago

This is a cool project.

It reminds me a bit of this multi-year, labor-of-love project: http://www.starryexpanse.com

Firehawke2• 6 years ago

I'm curious if they'd tried using CHD. It's worked pretty well for MAMEdev, and even the RetroArch core versions of a few emulators support it.

Dolphin Progress May and June 2020

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