Bungie sure packs them in

For the record, my previous post wasn't intended to be focused on Valve in particular (but of course any mention of the big V will be latched on). I used V's offices as an example because it's the last open office environment I've experienced, and it sucked probably more than it should have due to a company culture that had utterly failed to adapt as the company scaled from a few dozen to hundreds of developers.

If I could go back in time, I would have inserted more examples from other companies. My major concern before I hit publish was pissing off the open office zealots who ignore the science.

Anyhow, Bungie's offices are literally right up the street from Valve's, so let's see what they look like. At least this space has high ceilings, so it probably doesn't feel as claustrophobic as V's and background noise doesn't propagate so much. Nonetheless, it still looks like a cattle pen to me:

One forum comment (by IISANDERII) about this pic:

"Beginning to understand why they wanted to make players suffer and grind in Destiny. It was a silent revolt. I got a feeling it didn't look like this 15yrs ago."

I think very high ceilings are an important component of making open office spaces work at all, along with a company culture actually compatible with the open expression of ideas. Also, bad company culture can massively amplify the worst aspects of open office spaces.

The reality is, this is a very competitive industry, and it's difficult and expensive to hire skilled/experienced developers. The smart employers will realize that things like enforced industrial-sized cabal rooms and toxic peer-based stack ranking systems are boneheaded ideas and they'll come up with competitive alternatives to attract the best people. Ignoring the science and developer feedback to get X more hats live pronto is not smart.

Having experienced pretty much all possible layouts in my career, I would like to see a combination: A central room for say 15 people, surrounded by a large number of 1, 2, or 3 person offices, with at least 2-3 ways of leaving the central area. The small offices should resemble Ensemble's or Microsoft's: each with a door and a small vertical window near the door. Devs should be able to work where they want. Sometimes it makes sense to work together and collaborate, and sometimes you just need to concentrate. Usable whiteboards distributed throughout the space are critical.

Sheetrock, doors, whiteboards and glass are very cheap these days. These things are much less expensive to a company vs. the cost of a developer's time.

Open Office Spaces and Cabal Rooms Suck

Caught this new article in the Washington Post:
Google got it wrong. The open-office trend is destroying the workplace.

In case it wasn't clear: I really dislike large open office spaces. (Not 2-3 person offices, but large industrial scale 20-100 person open office spaces of doom.) Valve's was absolutely the worst expression of the concept I've ever experienced. I can understand doing the open office thing for a while at a startup, where every dollar counts, but at an established company I just won't tolerate this craziness anymore. (See the scientific research below if you think I feel too strongly about this trend.)

As an engineer I can force myself to function in them, but only with large headphones on and a couple huge monitors to block visual noise. I do my best to mentally block out the constant audio/visual (and sometimes olfactory!) interruptions, but it's tough. It's not rocket science people: engineers cannot function at peak efficiency in Romper Room-like environments. 

In case you've never seen or worked in one of these horrible office spaces before, here's a public shot showing a small fraction of the Dota 2 cabal room:

I heard the desks got packed in so tightly that occasionally a person would lower or raise their desks and it would get caught against other nearby desks. One long-time Valve dev would try to make himself a little cubicle of sorts by parking himself into a corner with a bunch of huge monitors on his desk functioning as walls, kind of like this extreme example:

He also had little mirrors on the top of a couple monitors, so he could see what people were doing behind him. At first I thought he was a little eccentric, but I now understand.

After a while I realized "Cabal rooms" (Valve's parlance for a project-specific open office space) resembled panopticon prisons:

See that little cell in the back left there? That's your desk. Now concentrate and code!

Here's the list of issues I encountered while working in cabal (open office layout) rooms:

1. North Korea-like atmosphere of self-censorship:

Now at a place like my previous company, pretty much everyone is constantly trying to climb the stack rank ladders to get a good bonus, and everyone is trying to protect their perceived turf. Some particularly nasty devs will do everything they can to lead you down blind alleys, or just give you bad information or bogus feedback, to prevent you from doing something that could make you look good (or make something they claimed previously be perceived by the group as wrong or boneheaded).

Anyhow, in an environment like this, even simple conversations with other coworkers can be difficult, because all conversations are broadcasted into the room and you've got to be careful not to step on the toes of 10-20 other people at all times. Good luck with that.

2. Constant background noise: visual, auditory, olfactory, etc.

As an engineer, I do my best (highest value) work while in the "flow". Background noise raises the mental cost of getting into and staying in this state.

3. Bad physical cabal room placement: Don't put a cabal room next to the barber or day care rooms people (!).

4. Constant random/unstructured interruptions. 

It's can be almost impossible to concentrate on (for example) massive restructurings of the Source1 graphics engine, or debugging the vogl GL debugger with UE4 while the devs next to you are talking about their gym lessons while the other dude is bragging about the new Porsche he just bought with the stock he sold back to the company.

5. Hyper-proximity to sick co-workers.

Walls make good neighbors, especially after they've caught a cold but feel pressured to be seen working so they come in anyway.

6. Noise spike in the afternoon in one cabal room, as everyone all the sudden decides to start chatting (usually about inane crap honestly) for 30-60 minutes. There's a feedback effect at work here, as everyone needs to chat louder to be heard, causing the background noise to go up, causing everyone to speak louder etc. Good luck if you're trying to concentrate on something.

7. Environmental issues: Temperature either too high or too low, lighting either too bright, too dark, or wrong color spectrum. Nobody is ever really happy with this arrangement except the locally optimizing bean counters.

8. Power issues or fire hazards due to extreme desk density.

9. Mixing electrical or mechanical engineers (who operate power tools, solder, destruct shit, etc.) next to developers trying their best to concentrate on code.

Related: Don't put smelly 3D printers etc. right next to where devs are trying to code.

10. Guest developers causing trouble:

Hyper-competitive graphics card vendors would watch the activity on our huge monitors and get pissed off when we emailed or chatted, even about inane crap, with other vendors.

Some guest developers treated coming to Valve like an excuse to party. We learned the hard way to always separate these devs into separate mini-cabal rooms.

11. No (or bad access to) white boards.

At Ensemble Studios (Microsoft), each 2-3 person office had a huge whiteboard on one wall. This was awesome for collaboration, planning, etc. 

More articles on the nuttiness of open office layouts:

Open-plan offices make employees less productive, less happy, and more likely to get sick

Study: Open Offices Are Making Us All Sick

The Open Office Trap

http://www.jstor.org/discover/10.2307/255498?sid=21105543363653&uid=4&uid=2

http://www.sciencedirect.com/science/article/pii/S0272494413000340

Example of a GOOD office space:

http://www.joelonsoftware.com/items/2006/07/30.html

Here's a quick summary of the scientific research (from The Open Office Trap):

"The open office was originally conceived by a team from Hamburg, Germany, in the nineteen-fifties, to facilitate communication and idea flow. But a growing body of evidence suggests that the open office undermines the very things that it was designed to achieve. In June, 1997, a large oil and gas company in western Canada asked a group of psychologists at the University of Calgary to monitor workers as they transitioned from a traditional office arrangement to an open one. The psychologists assessed the employees’ satisfaction with their surroundings, as well as their stress level, job performance, and interpersonal relationships before the transition, four weeks after the transition, and, finally, six months afterward. The employees suffered according to every measure: the new space was disruptive, stressful, and cumbersome, and, instead of feeling closer, coworkers felt distant, dissatisfied, and resentful. Productivity fell."

"In 2011, the organizational psychologist Matthew Davis reviewed more than a hundred studies about office environments. He found that, though open offices often fostered a symbolic sense of organizational mission, making employees feel like part of a more laid-back, innovative enterprise, they were damaging to the workers’ attention spans, productivity, creative thinking, and satisfaction. Compared with standard offices, employees experienced more uncontrolled interactions, higher levels of stress, and lower levels of concentration and motivation. When David Craig surveyed some thirty-eight thousand workers, he found that interruptions by colleagues were detrimental to productivity, and that the more senior the employee, the worse she fared."

"Psychologically, the repercussions of open offices are relatively straightforward. Physical barriers have been closely linked to psychological privacy, and a sense of privacy boosts job performance. Open offices also remove an element of control, which can lead to feelings of helplessness. In a 2005 study that looked at organizations ranging from a Midwest auto supplier to a Southwest telecom firm, researchers found that the ability to control the environment had a significant effect on team cohesion and satisfaction. When workers couldn’t change the way that things looked, adjust the lighting and temperature, or choose how to conduct meetings, spirits plummeted."

Ultimately, I noticed the biggest proponents of open office spaces have no idea how programmers actually work, aren't up to date on the relevant science (if they are aware of it at all), and in many cases do their best to actually avoid working in the very open office spaces they enforce on everyone else.

State of Linux Gaming

I've got one more blog post before I depart for Dallas. Here's an interesting report showing framerates and loading times of various big titles on Linux vs. Windows:

Slashdot: PCGamingWiki Looks Into Linux Gaming With 'Port Reports'
PC Gaming Wiki: Linux port report

Sadly, it's pretty clear that if you run these games on Linux your experience isn't going to be as good, and you'll be getting less "gaming value" vs. Windows. We're not talking about a bunch of little indy titles, these are big releases: Borderlands: The Pre-Sequel, Borderlands 2, Tropico 5, XCOM: Enemy Unknown, Sid Meier's Civilization V. My take is the devs doing these ports just aren't doing their best to optimize these releases for Linux and/or OpenGL.

A nice little tidbit from this report: "Unfortunately, Aspyr are currently still unable to provide support for non-Nvidia graphics cards, as with Borderlands 2. This doesn't mean the game won't work if you have an AMD or Intel GPU, but just that you're not guaranteed to receive help from the developer - the current driver situation for non-Nvidia cards may lead to degraded performance." Huh? This is not a good situation.

I know it's possible for Linux ports to equal or outperform their Windows counterparts, but it's hard. At Valve we had all the driver devs at our beck and call and it was still very difficult to get the Source engine's perf. and stability to where it needed to be relative to Windows. (And this was with a ~8 year old engine - it must be even harder with more modern engines.) These devs are probably glad to just release anything at all given how alien it can be for Windows/Xbox devs to develop, debug, and ship stuff under Linux+OpenGL.

Hey, this is just a thought, but maybe Valve developers could stop locally optimizing for their bonuses by endlessly tweaking and debugging various half-broken dysfunctional codebases and instead do more to educate developers on how to do this sort of work correctly.

The entire Intel driver situation remains in a ridiculous state. I know Intel means well and all but really, they can do better. (Are they afraid of pissing off MS? Or is this just big corp dysfunctionalism?) Valve is still paying LunarG to find and fix silly perf. bugs in Intel's slow open source driver:

Major Performance Improvement Discovered For Intel's GPU Linux Driver

Surely this can't be a sustainable way of developing a working driver?

Anyhow, onto SteamOS/Steambox. Here's a surprisingly insightful comment I found on Slashdot. I don't agree that SteamOS is done just yet, but you've got to wonder what is really going on. (So where are all those shiny Steam machines they showed earlier this year anyway? Does all this just go into the Valve memory hole now?)

Re:Gabe Newell is perhaps the biggest driver of th (Score:1, Interesting)

by Qzukk (229616) on Friday October 24, 2014 @11:56AM (#48222551) Journal

Let's be honest, SteamOS is done. Steam got exactly what they wanted from Microsoft and dropped it like a hot potato (so sorry, you'll never get to use that cool controller).

Consider that for decades Microsoft has not allowed anyone, anyone to touch the user experience. Even after Netscape's antitrust lawsuit over active desktop, even after BeOS withered and died hoping someone would sell a windows computer with dualboot, or hell just a windows computer with a "Setup BeOS" icon on the desktop. Steam is facing the Microsoft Store and a real threat that the Microsoft Store will become the way to buy programs (see also: iOS). Steam trots out SteamOS, and Microsoft snickers. The hype train builds up, and Microsoft sweats. Games start to port and Microsoft snaps.

Alienware ships a Windows 8 PC that boots to Steam instead of Metro.

Now, let's step back a second and look at the big picture here. At the time, windows 8 adoption is absolute total shit, swirling the drain of a public restroom that hasn't been washed for years. The last windows evangelists are all hanging on imploring people to just try it out, just give it a chance, and oh by the way install Start8 to fix metro. Think about that. PC vendors are on the verge of revolt, their customers refuse to buy their goods, and all for the want of installing a $5 program to fix the metro experience. Best Buy is probably screaming at Microsoft, begging them to allow them to remove the metro experience so they can move their inventory. Hell, they're probably begging them to let them advertise their Geek Squad services to "optimize" the experience and install that $5 program for $100. But no, the Microsoft Experience is inviolate, the holiest of holies, eternally immutable. No matter how much hatred it gets, it Must. Not. Be. Changed .

And then Alienware ships a Windows 8 PC that boots to Steam instead of Metro.

SteamOS's job is done. When no-one was looking, Steam took Microsoft and snapped it like a twig. We'll never know exactly what dark magicks were invoked here, but in the blink of an eye, Valve routed Microsoft in a war that nobody even realized was being fought. When Japan makes an anime out of this event, GabeN will point at Steve Ballmer, say omae wo shindeiru and Ballmer's head will implode, without GabeN throwing a single visible punch.

Steam OS will probably putter along, we'll probably see a few things be trotted out to keep the dream alive, after all the hype train did build up a lot of steam (pun not intended). Eventually a few of these AAA developers will say "it's really just not ready for the prime time" and we'll go back to getting a few wine ports and indie games from hardcore dedicated guys who just really love Linux.

But the masses will probably never get to hold that controller.

Interesting Talks and Articles

What Your Culture Really Says

https://web.archive.org/web/20131025031855/http://blog.prettylittlestatemachine.com/blog/2013/02/20/what-your-culture-really-says/

Open Office Layouts
http://qz.com/85400/moving-to-open-plan-offices-makes-employees-less-productive-less-happy-and-more-likely-to-get-sick/

http://blogs.wsj.com/atwork/2014/02/25/study-open-offices-are-making-us-all-sick/

http://www.newyorker.com/business/currency/the-open-office-trap

Narcissistic Leadership
http://www.maccoby.com/Articles/NarLeaders.shtml
http://www.spring.org.uk/2011/09/the-problem-with-narcissistic-leaders.php

Talks on the Science Behind Motivation, or why bonuses don't work

Dan Pink: The puzzle of motivation (transcript):

http://www.ted.com/talks/dan_pink_on_motivation?language=en

Kathy Sierra: "The Secrets of the Whisperers" (motivation and gamification)
https://www.youtube.com/watch?v=QNsl5D-V8T0&app=desktop

For Best Results, Forget the Bonus
http://www.alfiekohn.org/managing/fbrftb.htm

Why Bonus Systems Don't Work
http://brodzinski.com/2013/11/bonus-systems-dont-work.html

Joel on Software

Things you Should Never Do (or why code rewrites don't work)
http://www.joelonsoftware.com/articles/fog0000000069.html

Great offices for programmers:
http://www.joelonsoftware.com/articles/FieldGuidetoDevelopers.html
http://www.joelonsoftware.com/articles/BionicOffice.html

The Joel Test: 12 Steps to Better Code
http://www.joelonsoftware.com/articles/fog0000000043.html

Incentive Pay Considered Harmful
http://www.joelonsoftware.com/articles/fog0000000070.html

The Price of Dev Happiness
http://blog.fogcreek.com/the-price-of-dev-happiness-part-one/
http://blog.fogcreek.com/the-price-of-dev-happiness-part-two/

Whaddaya Mean, You Can't Find Programmers?

http://www.joelonsoftware.com/articles/fog0000000050.html

Good History Lesson on OpenGL vs. Direct3D
http://programmers.stackexchange.com/questions/60544/why-do-game-developers-prefer-windows

Alex St. John: OpenGL vs Direct3D
http://www.alexstjohn.com/WP/2014/03/25/opengl-vs-direct3d-yawn/

Alex St. John: "Recruiting Giants"
http://www.alexstjohn.com/WP/download/Recruiting%20Giants.pdf

Paying Down Your Technical Debt
http://blog.codinghorror.com/paying-down-your-technical-debt/

Your Most Important Skill: Empathy
http://chadfowler.com/blog/2014/01/19/empathy/

The Unreasonable Effectiveness of C
http://damienkatz.net/2013/01/the_unreasonable_effectiveness_of_c.html

Moving back to Texas!

My five year, mostly sunless odyssey in the Seattle area is finally coming to an end. I'll be visiting occasionally, but I can't wait to move back to Dallas next month. Thanks to everyone at Valve for making the place such an amazing company to work at. Also, a huge thanks to the truly world class developers at Rad Game Tools for their key help during the Steam Linux launch and helping us kick start vogl's development. Without the devs at Rad a lot of the stuff we did over the past few years just would not have happened. (Umm Gabe, why don't you just buy these guys already and officialize the Valve "satellite office" in Kirkland?)

To the Linux and GL community, I feel bad about quitting Valve before completing vogl. (Not that something like vogl could ever really be completed!) In the couple months before I quit I did everything I could think of (wrote the wiki, got UE 4 compatibility, built the regression suite, wrote up a 6+ month itemized task roadmap, etc.) to ensure vogl's development would continue moving forward without me. From studying the changes made on vogl's github repo after I quit it certainly looks like the devs at Valve and LunarG have done a good job moving it forward.

I think it'll be 3 years or more before OpenGL-Next is usable and relevant to shipping products. So even though vogl's has little chance of scaling beyond GL v4.x, it should remain a useful tool for a long time. I may fork it one day if I have to do any hardcore GL development again.

More apitest related links and notes

More apitest related links:

OpenGL Stop Breaking my Heart

apitest results on AMD comparing various OpenGL and D3D11 approaches

Some important things about apitest and the results worth pointing out:

1. apitest results should not be compared vendor vs. vendor.

The test was not originally designed to be used in this way. Accurate benchmarking is surprisingly hard, and it's possible apitest's results are flawed or misleading in some way when compared vendor vs. vendor.

2. In many cases AMD's GL driver is within the same ballpark, or faster, compared to their D3D11 driver.

3. The relative sorted order of techniques is approximately the same on both vendors. 

This is good, because apps tend to use the slowest techniques and the authors are encouraging developers to use the faster approaches.

4. We're taking possible performance gains of 15x-20x, on drivers from both vendors.

5x-10x would be fantastic, 15x+ is amazing. 

Now all that's needed are drivers from all vendors that not only support these techniques, but handle them reliably and with reasonably consistent performance.

State of GL 4.x revealed via "apitest" benchmark

This excellent GL 4.x micro-benchmark that has been making waves recently is really interesting. Now that it's on Phoronix it's about as mainstream as it's going to get: NVIDIA Slaughters AMD Catalyst On Linux In OpenGL 4.x Micro-Benchmarks

At first glance the results sound great for NV: "The AMD Catalyst driver gets absolutely annihilated for these GL4 micro-benchmarks". But unfortunately it's bad news for everyone working in GL because it clearly demonstrates just how fractured and inconsistent the GL driver landscape actually is when the rubber hits the road.

Article: "DirectX Creator Says Apple’s Metal Heralds the End of OpenGL"

Links:

Alex. St John: "Direct3D, OpenGL, Metal, Full Circle"
Time: "DirectX Creator Says Apple’s Metal Heralds the End of OpenGL"

According to St. John: "Nearly twenty years later OpenGL still sucks for games, OpenGL drivers are STILL consistently broken across devices, OpenGL is still driven by CAD applications".

BTW - I'm no longer at Valve or working on vogl. And no, I'm not being paid by, nor do I know anyone still at Apple, lol.

How I learned to stop worrying and love OpenGL

Good summary of the OpenGL developer debate with links:

http://www.dayonepatch.com/index.php?/topic/107633-a-pretty-huge-debate-about-opengl-has-erupted-in-the-dev-community-involving-devs-from-valve-epic-firaxis-and-amd/

"This is quite technical, but I think this is very interesting considering what Valve is staking on OpenGL in regard to its future plans:

1. The debate started when Rich Geldreich from Valve (who is working on Vogl, Valve's OpenGL debugger) posted an entry on his blog called Things That Drive Me Nuts About OpenGL.  He also made a couple of Twitter posts here and here.

2. In response, Timothy Lottes, a senior rendering programmer at Epic who developed FXAA and TXAA while at Nvidia, posted this response on his personal blog.

3. Rick Geldreich the posted The Truth on OpenGL Driver Quality on his blog.  His Twitter post on this entry features quite a few responses.

4. Joshua Barczak, Firaxis's lead graphics engineer for the Civilization, agrees with Geldreich and posted this blog entry OpenGL Is Broken.

5. Epic's Timothy Lottes (as naturally expected) posted this response.

6. This caused AMD's OpenGL developer to post an angry tweet and another one from a former Nvidia developer who now works at Valve.

7.  Michael Marks, the tech director from Aspyr, shared his thoughts.  He also posted OpenGL Stop Breaking My Heart and The Impact of Apple's Limited OpenGL Support On Gaming.

8.  A Unity developer chimed in with Rant About Rants About OpenGL.

9.  Barczak posted a follow-up regarding OpenGL driver quality.

10.  Lastly, and somewhat unrelated, a Naughty Dog dev said LOL DX12 LOL."

"OpenGL Is Broken"

Good writeup by Joshua Barczak:
http://www.joshbarczak.com/blog/?p=154

Apple Metal API

Apple (a Khronos Group "promoter" member) "is introducing a new 3D API called Metal, which takes the place of OpenGL, allowing games to get ’10x’ faster draw rates":

https://developer.apple.com/library/prerelease/ios/documentation/Miscellaneous/Conceptual/MTLProgGuide/Introduction/Introduction.html

http://www.anandtech.com/show/8116/some-thoughts-on-apples-metal-api

So now we have DX12, Mantle, and now Metal..

The Truth on OpenGL Driver Quality

The driver landscape is something that any practicing GL dev must face unless you like having only a fraction of potential customers able to enjoy your product. (These are the drivers you'll have to work with in order to actually ship a product today or within the next year or so. If you're just a dev playing at home with one driver you'll probably not have to deal with any of this gritty real-world stuff.) 

If all you've ever done is use D3D then you better strap yourself in because the available GL drivers for Windows/Linux are all over the map. Here's my current opinion on driver quality:

Vendor A

What most devs use because this vendor has the most capable GL devs in the industry and the best testing process. It's the "standard" driver, it's pretty fast, and when given the choice this vendor's driver devs choose sanity (to make things work) vs. absolute GL spec purity. Devs playing at home use this driver because it has the sexiest, most fun to play with extensions and GL support. Most of what you hear about the amazing things GL will be able to do in order to compete against D3D12/Mantle are by devs playing with this driver. Unfortunately, we can't just target this driver or we miss out on large amounts of market share. 

Even so, until Source1 was ported to Linux and Valve devs totally held the hands of this driver's devs they couldn't even update a buffer (via a Map or BufferSubData) the D3D9/11-style way without it constantly stalling the pipeline. We're talking "driver perf 101" stuff here, so it's not without its historical faults. Also, when you hit a bug in this driver it tends to just fall flat on its face and either crash the GPU or (on Windows) TDR your system. Still, it's a very reliable/solid driver.

Vendor A supports a zillion extensions (some of them quite state of the art) that more or less work, but as soon as you start to use some of the most important ones you're off the driver's safe path and in a no man's land of crashing systems or TDR'ing at the slightest hickup.

This vendor's tools historically completely suck, or only work for some period of time and then stop working, or only work if you beg the tools team for direct assistance. They have enormous, perhaps Dilbert-esque tools teams that do who knows what. Of course, these tools only work (when they do work) on their driver.

This vendor is extremely savvy and strategic about embedding its devs directly into key game teams to make things happen. This is a double edged sword, because these devs will refuse to debug issues on other vendor's drivers, and they view GL only through the lens of how it's implemented by their driver. These embedded devs will purposely do things that they know are performant on their driver, with no idea how these things impact other drivers.

Historically, this vendor will do things like internally replace entire shaders for key titles to make them perform better (sometimes much better). Most drivers probably do stuff like this occasionally, but this vendor will stop at nothing for performance. What does this mean to the PC game industry or graphics devs? It means you, as "Joe Graphics Developer", have little chance of achieving the same technical feats in your title (even if you use the exact same algorithms!) because you don't have an embedded vendor driver engineer working specifically on your title making sure the driver does exactly the right thing (using low-level optimized shaders) when your specific game or engine is running. It also means that, historically, some of the PC graphics legends you know about aren't quite as smart or capable as history paints them to be, because they had a lot of help.

Vendor A is also jokingly known as the "Graphics Mafia". Be very careful if a dev from Vendor A gets embedded into your team. These guys are serious business.

Vendor B

A complete hodgepodge, inconsistent performance, very buggy, inconsistent regression testing, dysfunctional driver threading that is completely outside of the dev's official control. Unfortunately this vendor's GPU is pretty much standard and is quite capable hardware wise, so you can't ignore these guys even though as an organization they aren't very good with software. Basic stuff like glTexStorage() crashes (on a shipped title) for months on end with this driver. B's driver devs try to follow the spec more closely than Vendor A, but in the end this tends to do them no good because most devs just use Vendor A's driver for development and when things don't work on Vendor B they blame the vendor, not the state of GL itself.

Vendor B driver's key extensions just don't work. They are play or paper extensions, put in there to pad resumes and show progress to managers. Major GL developers never use these extensions because they don't work. But they sound good on paper and show progress. Vendor B's extensions are a perfect demonstration of why GL extensions suck in practice.

This vendor can't get key stuff like queries or syncs to work reliably. So any extension that relies on syncs for CPU/GPU synchronization aren't workable. The driver devs remaining at this vendor pine to work at Vendor A. 

Vendor B can't update its driver without breaking something. They will send you updates or hotfixes that fix one thing but break two other things. If you single step into one of this driver's entrypoints you'll notice layers upon layers of cruft tacked on over the years by devs who are no longer at the company. Nobody remaining at vendor B understands these barnacle-like software layers enough to safely change them.

I've occasionally seen bizarre things happen on Vendor B's driver when replaying GL call streams of shipped titles into this driver using voglreplay. The game itself will work fine, but when the GL callstream is replayed we'll see massive framebuffer corruption (that goes away if we flush the GL pipeline after every draw). My guess: this driver is probably using app profiles to just turn off entire features that are just too buggy.

Interestingly, Vendor B has a tiny tools team that actually makes some pretty useful debugging tools that actually work much of the time - as long as you are using vendor B's GPU. Without Vendor B's tools togl and Source1 Linux would have taken much longer to ship.

This could be a temporary development, but Vendor B's driver seems to be on a downward trend on the reliability axis. (Yes, it can get worse!)

On the bright side, and believe it or not, Vendor B knows the OpenGL spec inside and out - to the syllable. If you can get them to assist you, their advice is more or less reasonable about plain GL matters (not extensions).

Vendor C - Driver #1

It's hard to ever genuinely get angry at Vendor C. They don't really want to do graphics, it's really just a distraction from their historically core business, but the trend is to integrate everything onto one die and they have plenty of die space to spare. They are masters at hardware, but at software they aren't all that interested really. They are the leaders in the open source graphics driver space, and their hardware specs are almost completely public. These folks actually have so much money and their org charts are so deep and wide they can afford two entirely different driver teams! (That's right - for this vendor, on one platform you get GL driver #1, and another you get GL driver #2, and they are completely different codebases and teams.)

Anyhow, this vendor's HR team is smart: it directly hires open source wiz kids to keep driver #1 plodding forward. This driver is the least advanced of the major drivers, but it more or less works as long as you don't understand or care what "FPS" means. If it doesn't work and you're really motivated you can git your hands dirty and try to fix it and submit a patch. If you're really good at fixing this driver and submitting patches then you may get a job offer from this vendor.

Anyhow, driver #1 is unfortunately pretty far behind on the GL standard, but maybe in 1-2 years they'll catch up and implement the spec as of last year. But you can't ignore this driver because they have a significant and strategically growing market share. So as a developer who wants to reach this market, you can't afford to use those fancy extensions or the latest trendy "modern" GL supported by vendors A and B. You must do a min() operation across all the drivers and in many cases this driver gates what you can do.

Vendor C has no GL tools at all for either platform. Sorry - want to debug that graphics problem you're having? Welcome to 1999.

Vendor C - Driver #2

A complete disaster. This team's driver is barely used by any titles because GL on this platform is totally a second class citizen, so many codepaths in there just don't work. They can't update a buffer without massive, random corruption. This team will do stuff like give you a different, unique, buggy driver drop for every title in your back catalog for perf analysis or testing. This team will honestly ask you if "perf" or "correctness" is more important.

I've seen one well-known engine team spend over a year attempting to get their latest GL 4.x+trendy extensions backend working at all on this team's driver. Hey guys - this driver just doesn't work, just move on already and implement a plain GL 3.x backend with workarounds (just like togl and other shipping titles do today).

On the bright side, Vendor C feeds this driver team more internal information about their hardware than the other team. So it tends to be a few percent faster than driver #1 on the same title/hardware - when it works at all.

Other drivers:

In addition to the above major drivers, there are several open source drivers, mostly developed by the community, for hardware from vendors A and B. They tend to be behind the times from a GL perspective, but I hear they mostly work. I don't have any real experience or hard data with these drivers, because I've been fearful that working with these open source/reverse engineered drivers would have pissed off each vendor's closed source teams so much that they wouldn't help.

Vendor A hates these drivers because they are deeply entrenched in the current way things are done. These devs have things like mortgages and college funds (or whatever) to keep funding, so there's a massive amount of inertia from this camp. There's no way they are going to release their Top Secret GPU Specs to the public, or (gasp!) open source their driver. Vendor A will have to jump on the open source driver bandwagon soon in order to better compete against Vendor C's open model, whether they like it or not.

Vendor B halfheartedly helps their open source driver by funding a tiny team to keep the thing working. At some point, the open source driver for Vendor B's GPU may be a more viable path forward then their half-functional closed source driver.

Conclusion

To ship a major GL title you'll need to test your code on each driver and work around all the problems. May the "GL Gods" help you if you experience random GPU corruption, heap corruption, lockups, or TDR's. Be very nice to the driver teams and their managers/execs, because without them your chances aren't nearly as good.

Things that drive me nuts about OpenGL

Here's a brain dump of the things that sometimes drive me crazy about OpenGL. (Note these are strictly my own opinions, not those of Valve or my coworkers. I'm also in a ranty-type mood today after grappling with OpenGL for several years now..) My major motivation to posting this: the GL API needs a reboot because IMO Mantle/D3D12 are going to most likely eat it for lunch soon, so we should start talking and thinking about this stuff now.

Some are minor issues, and some are specific to tracing the API, but all these issues add up to API "friction" that sometimes make it difficult to encourage other devs to get into the GL API or ecosystem:

1. 20 years of legacy, needs a reboot and major simplification pass
Circle the wagons around a core-style API only with no compatibility mode cruft.
Simplify, KISS principle, "if in doubt throw it out"!
Mantle and D3D12 are going to thoroughly leave GL behind (again!) on the performance and developer "mindshare" axes very soon.
Global context state and the binding pattern sucks. The DSA (direct state access)-style API should be standard/required.

Some bitter medicine/tough love: Most devs will take the easy path and port their PS4/Xbone rendering code to D3D12/Mantle. They will not bother to re-write their entire rendering pipeline to use super-aggressive batching, etc. like the GL community has been recently recommending to get perf up. GL will be treated like a second-class citizen and porting target until the API is modernized and greatly simplified.

2. GL context creation hell:
Creating modern GL contexts can be hair raisingly and mind numbingly tricky and incredibly error prone ("trampoline" contexts anyone?). The process is so error prone, and platform (and occasionally even driver) specific that I would almost always recommend to never go directly to the glX, wgl, etc. API's, and instead always use a library such as SDL or GLFW (and something like GLEW to retrieve the function/extension pointers).

The de-facto requirement to always pick from a small set of large 3rd party libraries just to get a real context rolling sucks. The API should be simplified and standardized so using a 3rd party lib shouldn't be a requirement just to get a real context going.

3. The thread's current context may be an implied "this" pointer:
Function pointers returned by GetProcAddress() cannot (or should not - depending on the platform!) be used globally because they may be strongly tied to the context ("context-dependent" vs. "context-independent" in GL-speak). In other words, calling GetProcAddress() on one context and using the returned func pointer on another is either bad form or just crashes.
So is GL a C API or not?
Can we just simplify and standardize all this cruft?

4. glGet() API deficiencies:
This is probably too tracing specific, but it impacts regular devs indirectly because if the tools suck or are non-existent because the API is hard to trace your life as a developer will be harder.
The glGet() series of API's (glGetIntegerv, glGetTexImage, etc.) don't have a "max_size" parameter, so it's possible for the driver to overwrite the passed in buffer depending on the passed in parameters or even the global context state. These functions should accept a "max_size" parameter and the functions should fail if the supplied max_size is too small, not overwrite memory.
Computing the exact size of texture buffers the driver will read or write depends on various global context state - bad bad bad.
There are hundreds of possible glGet() pname enum's, some accepted by only some drivers. If you're writing a tracer or some sort of debug helper, there is no official way to determine how many values will be written by the driver given a specific pname enum. There are no official tables to determine if the indexed variants of glGet() can be used with a specified enum, or determine the optimal (lossless) type to use given a specific enum.
Also, the behavior of indexed vs. non-indexed gets & sets is not always clear to new users of the API.
Alternately, perhaps just add some glGet() metadeta API's vs. publishing tables.

5. glGetError()
There is no glSetLastError() API like Win32, making tracing needlessly complex.
Some apps never call it, some call it once per frame, some only call it while creating resources. Some call it thousands of times at init, and never again. I've seen major shipped GL apps with per-frame GL errors. (Is this normal? Does the developer even know?)

6. Can't query key things such as texture targets
(I know some of this is being worked on - thanks Cass!) This makes tracing/snapshotting more complex due to shadowing.
Shadowing deeply interacts with glGetError()'s (we can't update our shadow until we know the call succeeded, which involves a call to glGetError(), which absorbs the context's current GL error requiring even more fancy footwork to not diverge the traced app's view of GL errors).

About the recent talk of getting rid of all glGet()'s: IMO either all state should be queryable (which is almost the case today), or the API should be written with maximum perf and scalability in mind like D3D12/Mantle. The value added by the API is clearly understood in either of these extremes.
Getting rid of glGet()'s will make writing tracers & context snapshotters even trickier.

7. DSA (Direct State Access) API variants are still not standard and used/supported everywhere
DSA can make a huge difference to call overhead in some apps (such as Source1's GL backend). Just get rid of the reliance on global state, please, and make DSA standard for once and for all.

8. Official spec is still not complete in 2014:
The XML spec still lacks strongly typed param information everywhere. For example:

 <command>
    <proto>void <name>glBindVertexArray</name></proto>
    <param><ptype>GLuint</ptype> <name>array</name></param>
    <glx type="render" opcode="350"/>
  </command>

apitrace's glapi.py is still the only known public, reliable source of this information that I know of:

  GlFunction(Void, "glBindVertexArray", [(GLarray, "array")]),

Notice how glapi.py defines the type as "GLarray", while the official spec just has the nondescript "GLuint" type.

Add glGet info() to official spec: Mentioned above. How many values does the pname enum return? What are the optimal types to use to losslessly retrieve the driver's shadow of this state? Is the pname ok to use with the indexed variants?

9. GLSL version of the week hell:
For early versions, the GLSL version may not sync up with the GL version it was first defined in, making things even more needlessly confusing. And this is before you add in things like GLSL extensions (*not* GL extensions). Can be overwhelming to beginners.

10. No equivalent of standard/official D3DX lib+tools for GL:
Texture/pixel format conversion helpers that don't rely on using the driver or a GL context
KTX format interchange hell: The few tools that read/write the KTX format (GL's equivalent of DDS) can't always read/write eachother's files.
Devs just need the equivalent of Direct3D's DXTEX tool, with source.
The KTX examples just show how to load a KTX file into a GL texture. We need tools to convert KTX files to/from other standard formats, such as DDS, PNG, etc.
A GLSL compiler should be part of this lib (just like you can compile HLSL shaders with D3DX).

11. GL extensions are written as diffs vs the official spec
So if you're not a OpenGL Specification Expert it can be extremely difficult to understand some/many extensions.

Related: The official spec is written for too many audiences. Most consumers of the spec will not be experts in parsing it. The spec should be divided up into a developer-friendly spec vs a deeper spec for the driver writers. Extensions should not be pure delta's vs. the spec - who can really understand that?

12. Documentation hell
We've got 20 years of GL API cruft out there that adds noise to Google searching for GL API information, and beginners can get easily tripped up by bad/legacy documentation/examples.

13. MakeCurrent() hell
Can be extremely expensive, hidden extra variable cost with some extensions (I'm looking at you NV bindless texturing!), can crash drivers (or even the GPU!) if called within a glBegin/glEnd bracket, etc.
The behavior and performance of this call needs to be better specified and communicated to devs.

14. Drivers should not crash the GPU or CPU, or lock up when called in undefined ways via the API
Should be obvious by now. Please hire real testers and bang on your drivers!
Better yet: Structure the API to minimize the # of undefined or unsafe patterns that are even possible to express via the API.

15. Object deletion with multiple contexts, cross-context refcounting rules, "zombie" objects:
Good luck if the object being deleted is currently bound on another context.
Trying to call glGet()'s on a deleted object (that is still partially "live" because it's bound or attached somewhere) - behavior can differ between drivers.
All of this is needless overhead/complexity IMO.
Makes 100% reliable snapshotting and restoring GL context state very, very difficult.
I see world-class developers screw this up without knowing it, which is a clear sign that the API and/or tool ecosystem is broken.

16. Shader compiling/program linking hell
Major performance implications to shader compiling/linking.
Tokenized shader programs work. Direct3D is the existence proof that this approach works. The overall amount of pain GLSL has caused developers porting from D3D and end users (due to slow load times) is incredible, yet GL still only accepts textual GLSL shaders.
Performance drastically varies between drivers. Shader compiling can be effectively a no-op on some drivers, but extremely expensive on others.
Program linking can take *huge* amounts of time.
Some drivers cache linked programs, some don't.
Program linking time can be unpredictable: fast if the program is cached, but there's no way to query if the program is already cached or not. Also no way to query if the driver even supports caching.
Some drivers support threaded compilation, some don't. No way to query if the driver supports threaded compilation.
Some drivers just deadlock or have race conditions when you try to exploit threaded compilation.
Just a bad API, making it hard to trace and snapshot: Shaders can be detached after linking. Lots of linked program state is just not queryable at all, requiring link time shadowing by tracers.
Just copy & paste what D3D is doing (again, it works and devs understand it).

17. Difficult API to trace, replay, and snapshot/restore
Hurts tool ecosystem, ultimately impacts all users of API.
API should either be written to be easily traced/replayed/snapshotted, or incredibly performant/scalable like Mantle/D3D12. Right now GL has none of these properties, putting it in a bad spot from a value proposition perspective.
API authors should focus more on VALUE ADDED and less on how things should work, or how we are different from D3D because we're smarter.

18. Endless maze of GL functions (thousands of them!)
Hey - do we really need dozens of glVertexAttrib variants? Who really even uses this API?
API needs a reboot/simplification pass. Boost the "signal to noise" ratio, please.

19. Legacy complexities around v3.x API transition:
"Forward compatible", "compatibility" vs. "core" profiles etc. etc. etc.
Devs should not have to master this stuff to just use the API to render shaded triangles.
"Core" should not even be in the lexicon.

20. Reliably locking a buffer with DISCARD-semantics on all drivers without stalling the pipeline:
Do you use a map flag? BufferData() with NULL? Both, either, etc.?
What lock flag or flags do you use? Or does the driver just completely ignore the flag?
Trivial in D3D, difficult to do reliably in GL without being an expert or having direct access to driver developers.
This stuff is incredibly important!
Special note to driver developers: What separates the REAL driver devs from wannabees is how well you implement and test stuff like this. Pipeline stalling is not an option in 2014!

21. BufferSubData() stalls when called with "too much" data on threaded drivers
No way to query what "too much" data is. Is it 4k? 8k? 256k?

22. Pipeline stalling
No official (or any) way to get a callback or debug message when the driver decides to throw up its hands and insert a giant pipeline stall into your rendering thread
This can be the #1 source of rendering bottlenecks, yet we still have almost zero tools (or API's to help us build these tools) to track them down

23. Threaded drivers hell
Some manufacturers decide to forceably auto-enable their buggy multithreaded drivers months after titles have been shipped & thoroughly tested by the developer. (And to make matters worse, they do this without informing the developer of the "app profile" change or additions.)
Some multithreaded drivers have buggy glGet()'s when threading is enabled - makes snapshotting a nightmare.
No official way to query or control whether or not the driver will use multithreading.
No way to specify to the driver that a tracer is active which may issue a lot of glGet()'s (that the app would not normally do)
Bone headed threaded drivers that slow to an absolute crawl and stay there when an app or tracer constantly issues glGet()'s (just use a heuristic and automatically turn threading off!)

24. Timestamp queries can stall the pipeline on some drivers
Makes them useless for cross platform, reliable GPU profiling. GL spec should strongly define when the driver is allowed to stall on these queries. Unnecessary stalling should be redefined as a driver bug (by sometimes lazy/incompetent driver developers who don't understand how key these little API's can be).
For reference, NVidia does this stuff correctly. If you are a driver writer working on pipeline query code, please measure your implementation vs. NVidia's driver before bothering to release it.

25. GL is really X different API's (one per driver, sometimes per platform!) masquerading as a single API.
You can't/shouldn't ship a GL product until after you've thoroughly tested for correctness and performance on all drivers (in both threaded and non-threaded modes). You will be surprised at the driver differences. This came as a big shock to me after working for so long with D3D.
This indicates to me that Khronos needs to be more proactive at testing and validating the drivers. GL needs the equivalent of the WHQL process.

26. Extension hell
One of the touted advantages of GL is its support for extensions. I argue that extensions actually harm the API overall, not help it.

I've been through a large amount of major and minor GL callstreams (intricately!) over the previous ~1.5 years. (Before that I was the dev actually making togl work and be shippable on all the drivers. I can't even begin to communicate how difficult and stressful that process was 2+ years ago.) Excluding the driver devs I've probably worked with more real GL callstreams than most GL devs out there. Sadly, in many cases, some to many of the most advanced "modern" extensions barely work yet (and sometimes vendors will even admit this fact publicly). Or, if you try to use a cool-sounding extension you quickly discover that you're pushing a little-used (and tested) path down the driver and the thing is useless for all practical purposes.

From studying and working with the callstreams, it's apparent that devs do a massive MIN() operation across the functionality implemented on the available/targeted drivers. This typically means core profile v3.x, maybe also a 4.x backend with very simple/safe operations. (Or it's a small title that just uses compatiblity GL like it was still 1998 or 2003 - because that's all they need.) They don't bother with most extensions (especially the "modern" ones) because they either don't work reliably (because the driver paths that implement them are not tested on real apps at all - the classic chicken and egg problem), or they are only supported (sometimes barely) by 1 driver, or the value add just isn't there to justify expanding the product testing matrix even more.

Additionally, some of these modern extensions are very difficult to trace, which means that whatever debugging tools employed by the developer aren't compatible with them. So you need a fallback anyway, and if the devs must implement a fallback they might as well just ship the fallback (which works everywhere) and not worry about the extension (unless it adds a significant amount of value to the product).

So unless it's non-extended GL it might as well not be there to a large number of devs who just want to ship a reliable/working product.

Replay Divergence Hell

We've had a handful of traces in vogl that don't replay correctly hanging around in our regression test suite. One g-truc sample (gl-320-fbo-blit) was randomly failing -- turns out it wasn't clearing the backbuffer every frame. It was rendering a checkerboard of quads, so half the pixels in the backbuffer were not being written. Sometimes it would play back seemingly correctly (black pixels where quads weren't being rendered), and sometimes we would see random-looking bits in there.

Anyhow, I'm now trying to figure out why the g-truc sample gl-330-blend-rtt diverges when replayed with vogl. It's also randomly failing. Beyond Compare's image comparison mode can be pretty helpful in cases like this.

Update: OK, I found the problem. The sample uses a FBO with 3 texture attachments, but it was only clearing the first one in display(). The fix is simple:

for (int i = 0; i < 3; i++)
  glClearBufferfv(GL_COLOR, i, &glm::vec4(1.0f)[0]);

vogl Windows port, new regression test system, new vogl_chroot repo

Windows Port Progress

John McDonald has officially begun the Windows port of vogl. The voglcore lib and voglgen (our code generator tool) are now running on Windows as of this morning!

New Regression Test System

vogl has a shiny new tracing/replaying/trimming regression and smoke test system written by Mike Sartain that runs the following steps on a library of traces:

• Plays back either an apitrace or a vogl trace, captures its output using the libvogltrace SO, and records the backbuffer CRC's (or per-component checksums on traces with multisampling) to a text file.
• Plays back this trace and diffs the backbuffer CRC's vs. the CRC's seen during tracing.
• Finally, we trim the test trace, then play back the trimmed trace and compare the backbuffer CRC's vs. the original trace's CRC's. Trimming involves playing back the test trace up to a predetermined point, capturing the entire GL state vector to memory and serializing it out, so we get a lot of good coverage in this step.

The system is located in the test directory of vogl's chroot repository, here. The script that runs the test is run_tests.sh. (This little script actually compiles and launches a small .C file that contains the entire test system.) The file tests.json configures which traces are tested and the parameters to the various test steps. 

Currently, only our smallest traces (from the g-truc 3.x suite) are pushed up to vogl_chroot. We also have many GB's of game traces (please drop me a message if you would like these traces). It's pretty easy to add your own traces - I'll be documenting how on vogl's wiki this afternoon.

Here are some shots of it in action on our dual Xeon (20 core/40 HW thread) test machine, using "/run_tests.sh -j 6" - to spawn up to 6 parallel processes at a time vs. the default 4:

Interestingly, the limiting scaling factor on this system seems to primarily be GPU video memory, not raw CPU or GPU performance. Metro Last Light, TF2, and DotA2 each can use ~1 GB of VRAM (and we only have a 3GB 780 Ti on this system). We don't try to order the trace replay order in any particular way to optimize overall throughput, which would be a nice addition.

vogl_src and vogl_chroot repos

Thanks to Carl Worth (Intel OTC) and Sir Anthony for submitting some patches to help us break up the previously huge vogl repo into two smaller repos. The primary one on github contains only the (buildable) source:

https://github.com/ValveSoftware/vogl

And vogl_chroot is the optional portion we use internally to simplify building and testing vogl:

https://bitbucket.org/raddebugger/vogl_chroot

You don't strictly need vogl_chroot, but beware you'll need to manually figure out the build dependencies if you don't. Building both 32-bit and 64-bit vogl without using the chroot approach can be a huge pain due to sometimes unresolvable/obscure i386 vs. amd64 system dependency issues. (If you disagree, I claim you haven't tried to actually do it. And no, gcc-multilib is not enough.)

Next Steps

We've been supplied with more test traces from various teams working on titles that will be released later this year on Steam Linux. (Hey - if you're working on a new GL game or port, feel free to send us more traces!) Also, Rad Game Tools just provided us with a fresh drop of Bink video, which now supports using compute shaders to massively accelerate video decoding. I'll be adding support for its GL 4.x callstream next week.

vogl support for Unreal Engine 4

We're extremely excited that Epic is porting Unreal Engine 4 to Linux -- see the official announcement or some press here and here. Once we heard UE4 Linux was coming we pretty much dropped everything to ensure vogl can handle UE4 callstreams. The latest code on github now supports full-stream tracing/replaying and trimming of UE4 callstreams in either GL3 or GL4 mode. UI support for UE4 is still in the early stages, but now that we can snapshot/restore UE4 and continue to play back the callstream without diverging it's only matter of time before the UI comes up to speed.

UE4's OpenGL renderer is the most advanced we've worked with so far. It has provided us with valuable real-world test cases for several modern GPU features we've not had traces to validate our code against, such as compute shaders and cubemap arrays. We'll be making UE4 GL callstreams part of our regression test suite going forward.

Here are some shots of a trace of UE4's test game being replayed in voglreplay64's --interactive mode (which relies on state snapshotting/restoring):

Here's a trimmed trace loaded in the editor:

Known problems:

• UI: Peter Lohrmann just added a dropdown that lets you select which context's state to view. This code is hot off the presses and is a bit fiddly at the moment. Also, UE4 uses several texture formats that the vogl UI can't display right now (LunarG is helping us fix this, see below.)
• Snapshotting UE4 during tracing is currently unsupported (but snapshotting during replaying works), because the tracer can't snapshot state while any buffers are mapped. (We also have this problem with the Steam Big Picture renderer.) We have a fix in the works.
• We're seeing several query related warnings/errors while snapshotting and replaying UE4 callstreams. (This problem is in vogl's replayer, not UE4.) These need to be investigated, but they don't seem to cause the replayer to diverge.
• There are several "zombie" buffer objects that have been deleted on one context but remain bound on another, which causes the snapshot system to report handle remapping errors on these objects during snapshotting. These buffers don't appear to be actually referenced after they are deleted, so this doesn't cause the replay to diverge. We've got some ideas on how to improve vogl's handling of this scenario (which is unfortunately very easy to do by accident in GL).

Other news:

LunarG has provided us with the first drop of their universal OpenGL texture format converter/transformer module, which will be going open source soon. This module allows us to convert any type of OpenGL/KTX texture data to various canonical formats (such as 8-bit or float RGBA) in a driver independent manner, with the optional transforms we need to build a good texture/framebuffer viewer UI. The current vogl UI uses some temporary and very incomplete stand-in code to convert textures to formats Qt accepts, so we're really looking forward to switching to LunarG's solution.

Finally, John McDonald recently joined Valve and the SteamOS team and is currently getting up to speed on the vogl codebase.

couple vogl debugger/editor UI screenshots

vogl's UI (being worked on by Peter Lohrmann) has come far in the past month. I used it today while debugging what seemed to be a replay bug in Xonotic (reported by a dev named blackout24 on github). I first trimmed a single frame that clearly showed the problem, then played back this trimmed trace in a endless loop to verify the issue still showed up in the trim. I manually trimmed the source trace using voglreplay64, but I think initial support for doing all this directly from the UI just went in.

The UI helped me quickly pinpoint the first draw affected by the rendering problem. I then drilled down and examined all the GL state, textures, shaders, etc. on and around this draw. Clicking on a GL command that already had a snapshot was fast, only around a second in debug, and around 3-4 seconds on commands without snapshots. I still dumped the trimmed trace to JSON+loose files, more out of habit than anything, but using the UI was much faster than doing things the old way (which involved dumping massive amounts of PNG's on each major event, then using voglreplay -find and/or grep on huge JSON files).

Here's the pinpointed draw showing the problem (a completely opaque foliage billboard that should have been rendered transparently):

Depth and stencil buffers are currently displayed by mapping their individual bytes directly to image components - we're working on that.

Here's the foliage texture. I enabled alpha blending in the UI to double check the texture's alpha channel was reasonable:

Xonotic replay showing the problem, with the powerful QtCreator IDE in the background:

Turns out the problem was caused by Xonotic's usage of alpha to coverage on a multisampled default framebuffer. We don't currently support automatically enabling multisampling on default framebuffers during replaying. (We do of course support MSAA renderbuffers/textures/FBO's, but not on the default framebuffer yet.)

For now, I added a "-msaa X" command line option to the replayer to enable MSAA on the default framebuffer until we address this. This is crappy, but the vast majority of GL apps just don't enable MSAA this way and we have bigger fish to fry at the moment. (Also, I don't want to touch vogl's GLX/X-Windows related code until we abstract it away into SDL or something.)