User:Andrew Linden/SLDev Forum/2007 10 16

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Transcript of Andrew Linden's office hours:

[10:45] Glenn Linden: Hi, Alice
[10:46] Alice Klinger: oh hi Glenn
[10:46] Alice Klinger: sorry was afk lol
[10:46] Glenn Linden: NP - do you have voice?
[10:46] Alice Klinger: no
[10:47] Glenn Linden: OK, we'll do the session in text
[10:47] Alice Klinger: i could try set it up maybe i get it done in 13 mins lol
[10:48] Alice Klinger: well text is cooler to keep a copy anyways ty
[10:49] Kim Anubis: Hiya :)
[10:49] Alice Klinger: hi kim
[10:50] Alice Klinger: hi timeless
[10:50] Timeless Prototype: hiyas
[10:50] Kim Anubis: scan off
[10:54] Alice Klinger: hi andrew
[10:55] Kim Anubis: Hiya, Andrew
[10:55] Timeless Prototype: lol, hiya Andrew, I didn't even notice, my screen is filled with IMs (IM storm)
[10:55] Andrew Linden: Hello.
[10:55] Andrew Linden: Ah ha, there is a chair for me.
[10:55] Andrew Linden: hehe, I'm not allowed on this land, so I can't sit.
[10:56] Kim Anubis: lol
[10:56] Alice Klinger: hi count
[10:56] Count Bayliss: Hi All
[10:56] Kim Anubis: Hi, Count
[10:56] Timeless Prototype: hi Count
[10:56] Timeless Prototype: hi Itazura
[10:56] Itazura Radio: Hi Timeless
[10:57] Kim Anubis: Good to see you again, Timeless
[10:57] Timeless Prototype: likewise Kim :)
[10:57] Andrew Linden: There we go
[10:57] Andrew Linden: I've never participated in the SLDev forum before.
[10:57] Andrew Linden: How long has this been going on?
[10:57] Itazura Radio: That's makes two of us
[10:58] Itazura Radio: ;)
[10:58] Glenn Linden: I've been running them since May. we've had about 6 at this point.
[10:58] Timeless Prototype: Glenn is a hero
[10:58] Timeless Prototype: seriously
[10:58] Kim Anubis: I agree :)
[10:59] Andrew Linden: Today's topic is Havok4 since that is all I've been doing for the last year.
[10:59] Glenn Linden: Thanks (blush) - we've got such a great group of Solution Providers
[10:59] Andrew Linden: I probably won't say anything that hasn't already been said in another channel, but I can answer questions.
[10:59] Andrew Linden: I've got office hours now that Havok4 is in public preview.
[11:00] Andrew Linden: The next hours are tonight 16:30 - 17:30 at the Brampton Stage
[11:00] Seph Swain: hi.
[11:00] Alice Klinger: hi seph
[11:00] Kim Anubis: Hi
[11:00] Timeless Prototype: hi
[11:00] Andrew Linden: in case anyone doesn't get their questions answered.
[11:00] Itazura Radio: Hi Seph
[11:00] Glenn Linden: Great - thank you for joining us today, Andrew, and thanks all o fyou for coming.
[11:01] Glenn Linden: Andrew, what will we find different in Havok4.
[11:01] Andrew Linden: The main difference is that Havok4 should crash less.
[11:01] Alice Klinger: goodie :-)
[11:01] Andrew Linden: There is a mode where the Havok1 physics engine can block...
[11:02] Andrew Linden: for anywhere from a second to 20 minutes.
[11:02] Andrew Linden: We call it a "deep think"... it doesn't actually crash, but the simulator can't do anything else
[11:02] Andrew Linden: until it is done.
[11:03] Itazura Radio: I do that. Except I call it a brain fart.
[11:03] Andrew Linden: When that happens we eventually kill the simulator with a watchdog signal
[11:03] Andrew Linden: and it appears to be a crash to everybody inside or near the region.
[11:03] Andrew Linden: So, the primary thing changing in Havok4 is that "deep thinks" will hopefully be a thing of the past.
[11:03] Andrew Linden: The smaller changes...
[11:04] Andrew Linden: Some features may change subtlely
[11:04] Andrew Linden: there are some bugs that have been fixed...
[11:04] Andrew Linden: that required fundamental improvements to the physics engine before we coudl fix them
[11:05] Andrew Linden: the main one that comes to mind is that stacks of dynamic objects should "avtivate" whenever a supporting member is moved or deleted from the bottom of the stack.
[11:05] Andrew Linden: Lessee... what else....
[11:05] Andrew Linden: Not many new features
[11:05] Andrew Linden: some small ones are implicit spheres
[11:06] Andrew Linden: perfect spheres should roll like true spheres instead of faceted geometry
[11:06] Andrew Linden: but no new shapes no new LSL calls or big features like that.
[11:06] Andrew Linden: fin (next question)
[11:07] Glenn Linden: Andrew, will Havok 4 require changes to any scripts?
[11:07] Andrew Linden: Yes probably, but I'm not sure exactly which scripts or how the changes will have to be made.
[11:07] Andrew Linden: The problem is that some things will be changing in sublte ways
[11:08] Andrew Linden: and it is possible for scripters to "tune" their scripts to the current quirks of the physics engine
[11:08] Andrew Linden: a good example is when using LLSetForce() or whatever that call is.
[11:09] Andrew Linden: The force required for a particular bit of content may depend strongly on the fricition model of the physics engine
[11:09] Seph Swain: friction
[11:10] Andrew Linden: so the main breakage that will happen in scripts is in those scripts that will have "magic" numbers hard-coded into the script that are not flexible.
[11:10] Andrew Linden: I hope that the set of scripts that start to misbehave in havok4 is small.
[11:11] Andrew Linden: Megaprims...
[11:11] Andrew Linden: Currently the Havok4 preview still has some anti-megaprim code inside. I still need to pull that out.
[11:11] Andrew Linden: The plan for megaprims is to make them still partially supported (as broken as they are under Havok1)
[11:11] Andrew Linden: except...
[11:12] Andrew Linden: prims with dimensions larger than 256 will be clamped to 256.
[11:12] Glenn Linden: And as you have seen, there's a blog post asking for input on Megaprims.
[11:13] Andrew Linden: Glenn, why don't you post submitted questions to the main chat channel.
[11:13] Andrew Linden: That way I don't have to repeat them for everybody her3e.
[11:13] Kriz Janus: hrhr
[11:13] Rhianna Arkin: lol
[11:14] Glenn Linden: Megaprim question: Rhianna Arkin: they will be a limit of huge prims per SIM?
[11:14] Andrew Linden: No, there won't be a prim count limit of megaprims.
[11:14] Andrew Linden: That is, they'll be treated as regular prims, just like in Havok1.
[11:14] Glenn Linden: Question to Andrew: Gene Replacement has suggested making mega prims greater than a certain size forced to phantom, is this worth considering?
[11:14] Andrew Linden: Same semi-broken support for megaprims with the one caveat I mentioned.
[11:15] Andrew Linden: I'm not really interested in forcing the phatom bit for large prims.
[11:15] Andrew Linden: There have been some annecdotal useful uses of large prims for their collision properties
[11:16] Andrew Linden: one example that was given to me by someone here at LL
[11:16] Glenn Linden: Jet Control: How are the collision maps of sculpties to be in HAvok 4?
[11:16] Andrew Linden: was about how someone addd a single large prim to turn a large body of water into ice for a winter themed ice skate party
[11:17] Andrew Linden: As to handling the theoretical performance problems of megaprims..
[11:17] Andrew Linden: I've got some ideas. We may need to force objects above a certain size to be "static" and not allow them to go dynamic.
[11:18] Andrew Linden: If we do that, then there are some optimizations I can make to recover any performance problems they might pose.
[11:18] Andrew Linden: As to the collision shape of sculpties...
[11:18] Andrew Linden: That is a biggish project
[11:18] Andrew Linden: and we won't be working on it until after Havok4 is done
[11:19] Andrew Linden: the most important reason to get proper collision shapes for sculties that I know of
[11:19] Andrew Linden: is to help solve the "my neighbors objects overlap my parcel" problem
[11:19] Andrew Linden: I've got some ideas on how to use the physics engine to do object-parcel collision queries
[11:20] Glenn Linden: Another mega prim question: Rhianna Arkin: What will hapen with the current huge prims more than 256?
[11:20] Andrew Linden: but in order for it to work for sculpties I'll need to have better collision representations for them in the physics engine
[11:21] Andrew Linden: Megaprims larger than 256 on a side will have their scales clamped to 256 on those sides.
[11:21] Glenn Linden: Question: Kim Anubis: Hi, Glenn, here's a question: These days, if you have a bucket of physical prims, they won't ever settle down and completely stop moving. Will they behave this way with Havok 4?
[11:21] Andrew Linden: The problem of pile of objects not settling down may still be a problem in Havok4
[11:21] Andrew Linden: I haven't investigated that much yet.
[11:22] Andrew Linden: All the piles I've played with eventually settled down... unless I was using implicit spheres.
[11:22] Glenn Linden: Seph Swain: Can you tell us more about the time table ? Can I apply for testing it on my MainGrid Sim ?
[11:22] Andrew Linden: There is a known bug right now where large implicit spheres roll for a very loooooooong time... maybe forever.
[11:23] Andrew Linden: If piles don't settle down I may be able to make progress on that problem by tweaking some numbers in the physics engine.
[11:23] Andrew Linden: I suspect the problem is solvable in Havok4.
[11:23] Andrew Linden: I'm terrible at making time estimates.
[11:23] Andrew Linden: I'm always too optimistic.
[11:23] Andrew Linden: But we're getting close now so... a month maybe.
[11:24] Andrew Linden: As long as we don't have any really bad content bugs,
[11:24] Andrew Linden: and people can cross from H1 to H4 regions and back again
[11:25] Andrew Linden: then I'd be inclined to start deploying H4 to some regions early... maybe a sandbox or two in Second Life
[11:25] Andrew Linden: and eventually start allowing estate owners to opt into Havok4 simulators at their request.
[11:25] Andrew Linden: Currently there are two known crash bugs that I don't know how to fix.
[11:26] Andrew Linden: I've opened some support tickets with Havok. Hopefully we'll be able to fix those this week.
[11:26] Glenn Linden: Question from Itazura Radio: What are the implications/limitations of "static" vs "dynamic" megaprims in how they can/can't be used?
[11:26] Andrew Linden: There are some vehicle bugs that need to be fixed
[11:27] Andrew Linden: and the runtime collision control system (RCCS) which does object collision level of detail (LOD) needs work
[11:27] Andrew Linden: at the moment the RCCS might not be smart enough... it causes some objectionable artifacts
[11:28] Andrew Linden: however, the RCCS is the primary thing that prevents a Havok4 simulator from suffering too much lag
[11:28] Andrew Linden: Havok4 is faster than Havok1, but you can always throw more objects at it.
[11:28] Andrew Linden: Until it lags to death.
[11:28] Andrew Linden: Once you throw enough at Havok4 the RCCS is the only thing that keeps it "usable".
[11:29] Andrew Linden: Re the "static" vs "dynamic" megaprim question...
[11:29] Andrew Linden: Dynamic objects are managed by Havok4's "simulation island" system.
[11:30] Andrew Linden: Simulation islands are distinct piles of colliding objects
[11:30] Andrew Linden: and Havok4 uses the list of simulation islands to rapdly cull collision information each simualtion step.
[11:30] Andrew Linden: So....
[11:30] Andrew Linden: A very large prim will tend to bridge all simulation islands into one.
[11:31] Andrew Linden: As a result, the physics engine will not be able to cull the collisions as efficiently --> lag.
[11:31] Andrew Linden: Perhaps lag. How much is not known at this stage. I haven't experimented yet.
[11:31] Glenn Linden: Question from SaintSaens Writer: question for andrew, what steps are being taken to ease the problems related to physical movement with linked sculpted prims and Havok 4?
[11:32] Andrew Linden: If the megaprims are forced to be "static" then I can shift them into a different category of objects in the Havok4 physics engine.
[11:32] Andrew Linden: There is support in Havok4 for large objects that never move
[11:32] Andrew Linden: the simulation islands don't have to manage them, but things still collide correctly.
[11:33] Andrew Linden: But... if they are treated this way we an't allow them to sudddenly go dynamic at the whim of an LSL script.
[11:33] Andrew Linden: What are the problems with physical movement of linked sculpted prims?
[11:34] Andrew Linden: I need more context for that question.
[11:35] SaintSaens Writer: One of my developers has a test with a set number of prims, roughly 20, where he changes the position at the click of a button, if the prim is a sculpt, he can crash the sim with lag.
[11:35] Andrew Linden: Oh? In a Havok4 simulator?
[11:35] SaintSaens Writer: yes
[11:36] Andrew Linden: If so, then that is a bug and we'll try to fix it.
[11:36] Andrew Linden: Er... does the simualtor actually crash? Or does it just lag?
[11:36] SaintSaens Writer: great, there's a bug post on Jira and Dan Linden has the actual test object, I was just curious if you had more information about the issue.
[11:36] Andrew Linden: If it is a crash bug we're certainly going to try to fix it.
[11:37] Andrew Linden: If it is lag, we'll also try to fix that too.
[11:37] SaintSaens Writer: in one case it just lagged, another case I believe it crashed, it depended on the nature of the test.
[11:37] Andrew Linden: Not all bugs will block a release of the Havok4 project onto Second Life proper
[11:37] SaintSaens Writer: but by lag I mean, time dilation dropped to 0.2
[11:37] Andrew Linden: but the really bad ones will block the release.
[11:37] Glenn Linden: Andrew, what's the best way to report problems with Havok4 - via Issue Tracker?
[11:38] SaintSaens Writer: it's currently in the Issue Tracker, I was just curious if this was something that had come up internally.
[11:38] Glenn Linden: Question from Kim Anubis: I was also wondering if you have noticed any remarkable changes to the behavior of vehicles?
[11:38] Andrew Linden: The best way to report Havok4 problems is to file bugs or comment in existing bugs at
[11:38] Andrew Linden: I've been browsing the list and fixing the bugs that people have found.
[11:39] Andrew Linden: One problem with is that there is a little bit of a learning curve.
[11:39] Andrew Linden: There are multiples of categories under which you can file a bug
[11:40] Andrew Linden: and if you file a Havok4 bug as a "viewer bug" or a "web bug" it may get overlooked for a little while.
[11:40] Andrew Linden: Also, the list of bugs can get big, and anyone who doesn't take the time to examine the current list of bugs may enter duplicates.
[11:40] Andrew Linden: However, the system is working pretty well, and that is the recommended way to file a Havok4 bug, and many other sorts of bugs.
[11:41] Andrew Linden: I expect the LL developer interaction with to increase.
[11:41] Andrew Linden: It may eventually become the primary list of known problems.
[11:41] Andrew Linden: At the moment we have an internal system
[11:42] Andrew Linden: but if we wereto move things to then many things would be more transparent
[11:42] Andrew Linden: and we definitely want to move in that direction.
[11:42] Andrew Linden: There are internal discussions goin on about it right now.
[11:43] Andrew Linden: Kim asked about "remarkable changes to the behavior of vehicles"
[11:43] Andrew Linden: Kim could you elaborate on that?
[11:43] Andrew Linden: I wouldn't be suprised to find some vehicles significantly changed.
[11:43] Kim Anubis: Well, I have a book coming out in about a week, and one chapter focuses on an airplane script -- based on your basic airplane script, in fact
[11:44] Andrew Linden: Supporting vehicles as they were has been very difficult, and I don't think I've completely succeeded. I might not be able to succeed 100%
[11:44] Kim Anubis: I was wondering if it'll still fly once your Havok 4 deployment is all debugged and ready to roll out in the main grid.
[11:44] Andrew Linden: especially for vehicles that move along the ground.
[11:45] Andrew Linden: My hope is that airplanes will not be changed at all in the initial release of Havok4
[11:45] Kim Anubis: whew
[11:45] Andrew Linden: I've got some ideas on how to make better airplanes using some simple lift/drag/stall-speed model, but that is a new feature and is months away I'm sure.
[11:46] Andrew Linden: We certainly are not changing the LSL interface to vehicles in the short term
[11:46] Andrew Linden: I'm just working to make the old vehicles work as good or better than they did before.
[11:46] Glenn Linden: Question from Jet Control: How are the "friction" and/or "collision" properties of prim "materials" (glass , rubber, wood ect) effected?
[11:47] Andrew Linden: The friction effect in Havok is a bit different than Havok1.
[11:47] Andrew Linden: As it turns out... friction in Havok4 is probably "more correct" than Havok4.
[11:47] Andrew Linden: That is, a bit more like true friction.
[11:47] Andrew Linden: This has been the main problem with keeping ground vehicles moving along the terrain and roads in Havok4.
[11:48] Andrew Linden: But... I tried to make the friction and collision properties of the various materials equivalent to their behavior in Havok1.
[11:48] Andrew Linden: So my hope is that nothing has changed. If anything is drastically different then it should be filed as a bug.
[11:49] Glenn Linden: Question from Timeless Prototype: will I be able to send a test vehicle for use in testing?
[11:49] Andrew Linden: Currently I don't know of any such bugs. But I'm a little behind in browsing the list this week.
[11:49] Timeless Prototype: sent
[11:50] Andrew Linden: Yes, if you have any broken content you can send it to me. Preferably in the Havok4 preview so it shows up in my inventory there.
[11:51] Andrew Linden: It is better if you can post an example script in the public bug list, or provide some other simple recipe for reproducing the bug.
[11:51] Andrew Linden: That way, other developers beside myself can also work on it.
[11:51] Glenn Linden: Question from Count Bayliss: Question: Will Havok 4 help with sim crossings at all ?
[11:52] Andrew Linden: No, initially Havok4 will not change region crossings.
[11:52] Glenn Linden: Question from crucial Armitage: I don't work for Sun but I was just at the last CEC Sun Microsystems convention last week in Vegas and they announced there latest sun servers at the convention and from the looks of it and the specs of the servers one of these Sun Microsystems servers can run many regions in SL at the same time--is this something that could help ?
[11:52] Andrew Linden: That is... it isn't a problem with the physics engine, so much as a problem with serialization/deserialization of the objects as they cross the boundary.
[11:53] Andrew Linden: Region crossing is distinct from Havok4 and will be it own project when it comes to fixing it.
[11:53] Andrew Linden: Improving region crossings is an important project, and we may very well start it very soon after Havok4 is done.
[11:53] Andrew Linden: That is, I might be working on it. Not sure yet.
[11:54] Andrew Linden: No, I don't imagine we would use Sun servers.
[11:54] Andrew Linden: At the moment we build on inexpensive off the shelf hardware.
[11:54] Andrew Linden: We call it "bronze plated hardware".
[11:55] Andrew Linden: Sun sells silver or gold plated hardware... very expensive.
[11:55] Glenn Linden: We're near the end of our time today - any last questions for Andrew?
[11:55] Andrew Linden: I doubt the cost/performance ratio is right for using Sun.
[11:55] Andrew Linden: That said, I'm sure Ian Linden and some of the other Ops people could supply a better opinion than me on that.
[11:56] Timeless Prototype: just a big thanks from me, no questions outstanding :)
[11:56] Andrew Linden: I'm just guessing. I don't know much about the Sunhardware you're talking about.
[11:56] crucial Armitage: thanks being i was just at the convention i thought i mention it
[11:56] crucial Armitage:
[11:57] crucial Armitage: thats the new server if any one whats to see it
[11:57] Glenn Linden: One unrelated question from Rhianna Arkin: When windows vista will support second life? Is it more end of 2007 or summer 2008?
[11:57] crucial Armitage: just a thought i am in no way a tech expert *~~smiles~~*
[11:57] Andrew Linden: We don't yet have vista support for SL?
[11:57] Seph Swain: I'm using SL on Vista for half a year now.
[11:57] Andrew Linden: We have a couple of developers who are currently using vista on their dev machines.
[11:58] Andrew Linden: That question is somewhat related to Havok4 it turns out...
[11:58] Andrew Linden: one of the things we'll be able to do once Havok4 is merged into the main codebase
[11:58] Rhianna Arkin: sorry
[11:58] Andrew Linden: is to migrate to Visual Studio 2005 or whatever the latest version is
[11:58] Andrew Linden: which many of our developers, and the open source community is looking forward to
[11:59] Timeless Prototype: /me is afk, RL calls
[11:59] Andrew Linden: at the moment we're stuck on Visual Studio 2003 because Havok1 libs development is not available for 2005.
[11:59] Andrew Linden: Upgrading Vis Studio will help our own developers migrate to Vista I suspect.
[12:00] Andrew Linden: Well, I had fun answering all of your questions.
[12:00] Glenn Linden: Andrew, thank you very much for taking time to share with us today.
[12:00] Rhianna Arkin: thank you andrew
[12:00] Glenn Linden: Thank you all for coming. We'll post the transcript shortly.
[12:00] Count Bayliss: Thanks Andrew
[12:00] Itazura Radio: Thank you
[12:00] Kim Anubis: Thanks, Andrew & Glenn :)
[12:00] SaintSaens Writer: Thanks Andrew and Glenn
[12:00] Andrew Linden: Where does the transcript get posted?
[12:00] Alice Klinger: thanks everyone, was very interesting :-)
[12:01] Seph Swain: Yes, thanks! We're really looking forward to less sim crashes.
[12:01] Andrew Linden: As I mentioned, I also hold office hours today 16:30 - 17:30 if you have any more questions.
[12:02] Andrew Linden: An interesting thing about sim crashes under Havok4...
[12:02] Andrew Linden: under Haovk1 we had reached a state of apathy about solving sim crashes since we couldn't solve the deep think problem
[12:03] Andrew Linden: but now under Havok4, as soon as we find a new distinct crash mode we're very motivated to fix it.
[12:03] Seph Swain: 'apathy' is surely the right word :)
[12:03] Andrew Linden: So even if Havok4 goes out with some crash modes... I'm pretty sure we'll be able to fix them faster.
[12:03] Seph Swain: I'll take your word :)
[12:03] Andrew Linden: Yes, well when you've got 100 deep think crashes and you know you can't fix them...
[12:04] Andrew Linden: you're less motivated to search the pile for the 101st crash that wasn't a deep think.
[12:04] Andrew Linden: Just an interesting thing I noticed about "developer motivation"while working on this probject
[12:05] Andrew Linden: Ok, see you all later.
[12:05] Count Bayliss: CU
[12:05] Kim Anubis: Bye, Andrew. Thanks again :)
[12:05] Rhianna Arkin: bye, ty
[12:05] Jet Control: Great Session :)
[12:05] Seph Swain: Bye all.
[12:05] Glenn Linden: Thanks - I
[12:05] Seph Swain: Very interesting - and promosing :)
[12:05] Glenn Linden: I'll send a note to sldevgroup when we post the transcript.
[12:05] Kim Anubis: Thank you, Glenn -- these forums are really helpful
[12:06] Count Bayliss: Thanks Glenn
[12:06] Glenn Linden: Hope to see you next week at the Forum on the Directory and SP program!
[12:06] Kriz Janus: Yes, thank you ;)
[12:06] Kim Anubis: See you then!
[12:06] Glenn Linden: And Message Liberation on the 30th.
[12:06] Kim Anubis: I need to RSVP for that one
[12:06] Glenn Linden: And there's Andrew's office hours every Tuesday afternoon.
[12:07] Glenn Linden: Bye
[12:07] Kim Anubis: Bye, Glenn
[12:07] Rhianna Arkin: tyvm glenn
[12:07] Kriz Janus: Bye ;)
[12:07] Rhianna Arkin: bye
[12:07] Kim Anubis: Have a good afternoon, everyone!
[12:07] Count Bayliss: later gang