One of the goals of the 0.6.0 release is to replace the current IClientAPI interface with something that will improve compatibility down the road with alternative clients. Instead of our current model where we dictate the features that clients must support, the new model will allow clients to pick and choose features we handle, and then implement them.

The basic way this is handled, is through the new ‘IClientCore’ interface. We introduced the IClientCore interface within a few hours of version 0.6.0 being tagged - however switching to the interface internally will take some time - probably a month or two, so any projects using IClientAPI are still safe.

As many of you who have played with writing region modules will know, IClientAPI represents everything you can do to every possible client - as one may guess, this doesnt scale when you begin adding multiple different clients into the mix. It also makes things difficult when two clients have the same feature in radically different ways.

As you can see in the diagram above - all the particulars of IClientAPI are bundled up together as one common interface. It is convenient - but it’s also problematic when it comes to implementing a new client, as you need to stub out every single function - and modules cannot tell whether a particular event or function was simply ignored by the client as unsupported.

Enter IClientCore

IClientCore is presently a very narrow interface - we’re defining it as everything a client must support, whether it likes it or not. As a consequence - we’re sticking to things that every single client has and implements in a common manner.

In practice - this means IClientCore dictates only the Name, ID and other very common internal parameters. It also needs to support two new ’special’ interfaces - Get<IFace>() and TryGet<IFace>(IFace out). These last two are the keys to how the new system works.

Under the new system - we implement interfaces for Chat, Primitives, and each seperate functionality group. It’s then possible to use, ‘IClientCore.TryGet<IClientChat>(…)’ which returns an interface to this clients IChat interface. If the client doesnt support chatting - then TryGet returns false.

The first most obvious question to arise here is related to how this looks more complicated than it used to be, and that’s definetely true - where we differ is that the new model means you need to check a client supports something before attempting to use it.

Previously we had no way from modules to indicate whether a feature was supported on clients - and we also had no way of handling extensions. This also means that if you choose to implement a new Client adapter for OpenSim, you dont need to implement the previous 350 functions and ignore any custom ones. You can write new interfaces for your custom features, and only implement interfaces from the Linden Viewer where you think you share enough functionality to make it useful.

In most cases - the changes arent fairly significant, you can see a comparison of two functions under the old and the new in the porting guide I wrote.

If anyone has any comments or questions relating to this, please let me know.

Previously…

For those who havent been reading up on the OpenSim IRC channels or mailing list, your probably not aware of the work we’re doing at DeepThink for the realXtend team.

For the last month and a half, we’ve been working with the realXtend team to convert their version of OpenSimulator, to something that closer resembles a suite of OpenSim plugins rather than a fork. Part of this work has been some sponsored contributions to improving the modularity of OpenSim itself with alternate clients (like the IClientAPI changes that are currently in progress), the other part has been conversion of the current realXtend server into a single plugin DLL called ‘ModularRex.dll’ which encompasses all the previous internal changes.

The single biggest bit of news however is, once this is done - realXtend is no longer a fork of OpenSim. It’s not opensim stock, but it’s not a seperate codebase either. Patches from realXtend can be applied fairly smoothly towards OpenSim-trunk and vice-versa, because the core files are unchanged.

Now we’re not done yet, but we’re making some pretty steady progress to getting there by the end of the year - today marks the date at which the core architectural bits and pieces are mostly done and the realXtend server developers can get onboard and help finish the rest.

The code for the modular rex DLL’s is located on the forge project for it. It may not always represent the latest testing versions (since we’re working offline a lot), but we’re doing checkins every now and then - if you’re interested in following progress, that’s the best spot to go. Future development will be going on on the forge exclusively however.

Multiple Concurrent Clients

One of the largest feature’s we’ve now got with the latest version is the ability to insert clients into the scene while bypassing the normal login routines. This may not sound like much - but the technology needed to support this, is the same technology that will allow you to login with two completely different virtual world clients and have a conversation between them, while viewing potentially the same content.

The new ModularRex code skips all the current login methods and actually has a new subclassed and derived version which it enables entirely through a shared region module. In future - we may be able to take this same methodology and convert the current login and protocol handling routines into their own modules which allows them to be replaced without effort.

ModRex Support Table

Features

• Rex Avatars - We support all the packeting for the avatars now, however we do not automatically send this on login yet. If you know your rexav address, you can just type “/rexav http://somewhere.com/myav” in chat to set the parameter manually - or you can wait a few days now that we have login implemented and we can get to setting it automatically.
• Rex Logins - You can now login with a traditional rex username, that is you can login with “username@hostname.com”, and your authentication server will authorise you instead of a direct login.

Infrastructure

• Rex Packet Handling via RexClientView - We implement a IClientNetworkServer compatible interface which deals specifically with the modified realXtend protocol. This is subclassed from LLClientView / LLUDPServer / LLPacketServer but contains overrides and new methods to represent realXtend features.
• Rex Methods and Events on ClientView - We now process a number of the realXtend events and packets and fire new ‘OnRexXYZ’ events that you can use to send specific things to users. This does not effect IClientAPI, rather these are members of RexClientView which means you need to check the client supports features before using them. Currently, we’re sitting at about 13 of 36 handlers - however we’re 13/13[?] if you exclude methods related to RexPython (as of 0.31, there are likely going to be new things to support with the upcoming Rex release).

The TODO List

• Conversion to IClientCore - We started a lot of the conversion work before 0.6.0 was tagged, this means that the realXtend modules use a older method for checking client capabilities. We need to convert it to the new IClientCore interface to allow us standardised access to extension capabilities in modules.
• Finish SceneObjectGroup/SceneObjectPart Overloads - We’re inheriting and extending from the SOG/SOP interfaces to add additional rex-only properties to objects. There’s a degree of difficulty involved here which may nessecitate additional metadata fields in SOG/SOP. A post to OpenSim-dev will be coming shortly no doubt with some suggestions there. This is needed to be able to get rex meshes and other special object features working.
• Provide RexCommsManager - One of the limitations right now with the modular rex code is that Rex Logins (see above) dont provide a valid UserProfile class, because the Rex protocol there is different to OGS1. We need to provide an additional comms manager to allow Rex avatars to be handled correctly, or abstract OpenSim to allow ClientView to indicate the type of CommsManager it needs. This will also allow the global inventory features to be re-enabled (however moving them to the client may be a smarter long term move).
• Write generic LibRexAuth - A problem with the current dealings with the authentication server are that they are fairly hard coded for specific features. It would be nice to add a library or static class which can provide simple functions such as ‘GetProfileByAccountName’ or ‘IsUserAuthorised’ - this allows us to communicate better with the authentication server, saving hassle and headache and centralising things so that problems are more easily fixable. A similar class may be useful for the avatar server - however the simulator’s dealings with that server are very limited.
• Python - This needs to be converted a module, but shouldnt be too difficult as most of the code is presently abstracted and modular. With a little bit of work it may be possible to make realXtend python scripts editable in a similar manner to the LSL/C#/etc scripts, which would be very cool.
• Voice - As with the above, the Rex Voice Daemon is fairly seperate from the main codebase, so porting this should be a fairly quick and painless job.
• Update protocols to 0.35 - We’re currently sitting at the 0.31 release of realXtend which means there might be issues when the 0.35 realXtend viewer goes mainstream.
• Minor bits and bobs - Getting things such as the ODE Mesh Collisions working with realXtend collision meshes may nessecitate some additional work (and probably a subclassed version of our current ODE DLLs with additional functionality). There are probably a number of minor features and fixes that will need to be ported over once the main items on the TODO are done.

So overall, we’ve still got a lot of work to do - but the great news is all the architectural bits are just about done, and we’ve proven that such advanced functionality can infact be done entirely with the current OpenSim region modules.

Since we are on the verge of tagging the 0.6 OpenSim release, there’s a number of fundemental architectural changes we are investigating internally towards a path of more vendor neutrality. One of the changes I am proposing we make is to restructure SceneObjectGroup into part of the ClientStack heirachy rather than make assumptions about client representation models.

This is a proposal - it is not beyond reproach or comment.

The Current Model: SceneObjectGroup

Let’s begin by describing the current model - the largest limitation enforced on the current model is it dictates a method of heirachy which is fairly constrained. You have a parent who contains all the properties of the children, plus a few extra, then zero or more child primitives who are linked directly to the parent. The combined whole forms the ‘object’.

When you wish to modify a group property from a child, you need to check if you have a parent, if you do, modify the parent - but beware, certain things like the Position property mean different things as a child or root (why we also have AbsolutePosition and OffsetPosition properties to avoid confusion).

The obvious downsides of this approach are - we’ve made decisions that indicate that heirachical linking will never happen (something clients such as VastPark support via their nesting methods), neither is it possible to not have linking at all (ie say a standard Torque game). We’ve also got a mess of message routing which results in a very large number of if-null checks that perform different tasks depending on the outcome.

What should a revision also contain?

As part of the opportunity to fix this set of classes, we’ve got a chance to fix up some problems with SceneObjectGroup and SceneObjectPart - among them are, Vendor Neutrality (SOG/SOP is highly vendor specific), Multiple Linking models (ie not just Root->Children)

Strengthen IEntity - Derive More.

My personal favoured solution to this problem is to go back to IEntity and strengthen it up a bit. Right now, IEntity is a very minimalist interface dictating almost nothing about entities within the Scene, but it doesnt nessecarily need to be.

There are a number of properties which we can dictate as being universal about every entity regardless of the virtual world platform - these properties can be deemed as appropriate for a core interface, off the top of my head we can say the following are true of every type of ‘Entity’ we want to implement.

• ID - The internal number used to indicate the object ID.
• Position - The position of the entity inworld.
• Serialised Version - A version of the object which can be imported/exported easily (XML?)
• Physics Shell - The bounding box or triangle collection of this collection.
• Name?
• Scale?
• Rotation?
• BoundingBox?
  
• etc…

In the case of the Linden model specified above (SceneObjectGroup), the container becomes harder - we access our information about the object collection via the container. Physics shells are given for the container rather than every object inside, etc.

It also becomes possible to have multiple seperate models sharing the same scene simultaneously, each shares and communicates via the properties on IEntity. As a result, the scenegraph then resembles something like this.

A part overview

IEntity - Basic building block of objects contained in virtual worlds, it contains only properties which can be considered common to every virtual world platform.

LLEntity - This forms a replaceemnt for the current SceneObjectGroup, it contains properties which are applicable to the entire object, such as Owner, Permissions, Position and others. It contains a list of Children in the form of LLPrimitive. Unlike the current SceneObjectGroup, we do not utilise the .Root property from children to store group parameters. For instance, LLEntity.Root.OffsetPosition does not dictate where the entire object is located - as the root object, it will always be [0,0,0].

LLPrimitive - This contains a replacement for SceneObjectPart, unlike the current SOP it contains properties and methods only availible unique to the individual part. Properties which are shared among the group should be members of LLEntity instead. If you wish to access a group property it is always and only availible via LLEntity, and there are never members of LLPrimitive which simply act as ‘pass-thru’s to LLEntity. If you wish to access LLPrimitive - you must always access it via the parent group, it cannot be accessed via Entities directly.

XYZEntity - This is another entity from another world platform, it may have a heirachical linking situation where multiple entities in scene are chained together and share properties between each other internally. To the OpenSim perspective however we only see multiple seperate objects.

Potential Other IEntity Derivatives

In line with the above stated goal of supporting greater vendor neutrality I would like to propose some examples of other representations used today, and how we would be able to implement them under the new scheme mentioned above.

AWEntity (ActiveWorlds™) - While I’m not proposing to actually implement a AW Clientview, it’s representation of objects in scenegraph is fairly common and very similar to how game engines handle them. In ActiveWorlds, the world is a semi-finite plane divided into ‘cells’, each cell contains a number of objects however objects cannot link and have no notion of heirachy.

To implement AWEntity - we would implement all the common IEntity interfaces such as Position, Rotation, ID, etc. Then we would in addition implement some properties for the AW object parameters (Mesh Name, Object Name, Description, Client Script, etc).

We do not need to implement anything complex in terms of parents or children and the classes are without such properties. They contain a fairly ‘bare minimum’ scenegraph representation. (Just to repeat above, I have no plans to implement any such AW entity - this is just a hypothetical example using real world object representations)

Heirachical Entity (VastPark, Melanies Proposal, etc) - In this proposal, the same object consists of multiple independent parts. Each part has a collection of parents and children - however to Scene they are all independent seperate objects.

Each presents a seperate physics shell, each presents seperate property name and ID descriptions - however in special cases such as position or rotation, updating one reflects an update on the entire set simultaneously (or at least any descendants).

Handling the new objects internally

One of the largest problems of doing this (or any change) is that SceneObjectGroup is currently referenced in a very large number of places, making changes to it is likely going to result in a large number of structural changes needing to be done.

As an example of one of those changes - the following is a proposal on how to handle a single event in IClientAPI - OnNewEntity. The following represents the path that two independent IClientAPI implementations would follow in processing the same path.

The goal of this structure is to allow each client the opportunity to attempt to parse foreign object formats - if LLClientView understands XYZEntity enough to write a converter, then it can do so and send the converted result onto the Linden Viewer end user.

Likewise, if XYZClient understands Linden entities, then it can in turn write a converter to it’s internal packet representation and send the same object to it’s viewer.

In practice such converters will not be particularly easy to write - most Virtual Worlds use meshes in a variety of formats, so such converters may need to convert texture formats, mesh formats, etc. For LLClientView converters, it may simply be impossible to convert certain outside representations to something the viewer is capable of displaying and simply choose to display a lower detail representation, such as a bounding box of where the object should be.

To follow this process in detail, we’ll examine the LLClientView’s core processes.

In the first step (1), the Scene fires the OnNewEntity event which each client is listening for - as part of the event payload, the new entity is attached. This gets transmitted as a IEntity interface directly into the clientview.

Here the clientview needs to work out what kind of entity it is dealing with, it may do something like “if(IEntity is LLEntity) { … }” and handle appropriately (2).

As the LLClientStack is innately familiar with the structure of LLEntity, it can pretty much directly package it up to packets and prepare to send it to the end user (3).

However when it sees XYZEntity - XYZEntity is known to the ClientView, so it is capable of understanding it and potentially writing a converter (4) to the own internal packet formats. If we assume for a moment that XYZEntity is a AWEntity described above, then it may choose to create a temporary LLEntity which forms just a single box primitive and then package that up to the viewer.

Finally we’ve got something either in packets or close to it that we can quickly and easily send to the viewer (5). They are capable of seeing ’something’ for each Object in the scene, but naturally you need to be on a suitable client to see ever feature that platform supports.

Things unmentioned

One of the things I have left unmentioned is how to handle certain common tasks such as saving and restoring from the database. For the most part the infrastructure remains fairly similar - we can do a check ‘Is LLEntity’ in the DB adapters and follow the current path, or if we dont have one, we can use the IEntity.Serialise() method to get a text string for each entity which can be saved in the DB fairly easily.

In the case of restoring from the database however we need to in addition implement a IEntityFactory which can take a set of data (such as a serialised version) and restore it to an object, these EntityFactories could be installed via a Application or Region module.

Pardon this being a code-only post, but I figured it might be useful to anyone doing work with both OpenMetaverse and OpenSim - currently we store primitive data in a fairly different manner internally, this code converts between the two, and allows you to take a OpenMV.Primitive and get a OpenSim SOP out of it.

SineWave (with a little bit of help from DeepThink) is running a big Pub Quiz, this Friday on OSGrid.org. For those who are outside of Britan, read the wikipedia article for an overview on what this is, the rules and format.

The short

It’s on OSGrid.org, in the SineWave Region - 5PM GMT / 12PM EST / 9AM PST, Friday the 10th of October (this friday!). Total runtime is expected to be fourty minutes or so. You should register your avatar in advance on this page.

The rest

You should try test logging into SineWave sometime before the event, as we’ll be trying to start promptly. There’ll be other prizes including some hosting from DeepThink and maybe a little more. Performance will be a little slower than usual since the region will be operating under a performance profiler, but should still be acceptable.

As usual, we’ll publish the profiler results to help other developers - if you want to bring friends, feel free as the more avatars logged in, the better the quality of the results we get.

FAQ

Why are you running this, $500 is a lot to give away randomly? We’re doing this as a load test on OpenSim - we’re looking to get about 100 avatars or so and see where OpenSim stresses so we can optimise and fix those areas.

I need to get onto OSGrid - how do I connect? We recommend you grab the Hippo Viewer, it’s free and will connect by default to OSGrid (although it has support for any modern opensim grid)

I’ve been afflicted by this very problem myself lately, which is why this post has been sitting in my head (along with a slight hangover) for the last few days.

It should go without saying that a single developer can only achieve X number of features/fixes/improvements in Y time (and not every value of X is equal), but the moment you substitute “X” with specific feature names, it suddenly becomes urgent priority for everyone to stop work on it and get that done, to hell with everything else - although we want that too … and a pony.

The facts of life

The reality is - we’ve got a finite number amount of time, a finite number of developers, and a not-quite-so-finite list of features and improvements we have to spend time on, this means we prioritise stuff. We say “We think stability is a prerequisite before you go about implementing an example micropayments system.” - and with good cause, if the system didnt have that prerequisite stability, why the hell would you trust it to handle important or sensitive information?

This is not to say some of us havnt devoted time to thinking about it, it’s just that we each have our own ideas about what we think is important, and unless you are actively assisting in some capacity (food, booze, code, testing, etc), your personal wish list probably isn’t going to get any attention.

It’s harsh - but there it is. At the end of the day, each developer has a finite amount of time to work on projects, and when they are working on things - there is a strong chance that a specific goal is in mind and needed. If you want to change that goal, you either must have a convincing reason that that person is interested in and agrees with, or you need to provide an incentive to compensate for time that would otherwise be spent elsewhere. It’s also quite possible to just get in there, and do it yourself then submit those changes back.

Backseat Driving

There’s a lot of developers working on the OpenSim project - and each of them has their own ideas, goals and projects. Some of them are working on commercial projects that rely on OpenSim - and hence have some very specific feature and stability requirements that they work on. Others have more free reign by virtue of doing this in their spare time. There is a common misconception that the OpenSim team has an agenda - there’s somewhere around 200 developers on the project which means there’s 200 sets of agenda’s.

Right now, my personal agenda (which by proxy does carry a little across to what the DeepThink developers are working on) looks something like this:

• Abstract login and client initialisation to a more generalised interface to allow third party login and authentication routines to be fitted more easily as loadable DLLs.
• Find where we have remaining hard-coded references to LLClientView bits and bobs, and recode them in a more vendor neutral manner.
• Have a look at some of the terrain control issues reported on the mailing list recently.

It’s a pretty short list - this list gets revised, updated and changed pretty regularly based on what I need to do at the very moment, it’s the same for a lot of the other central developers - they are built on a task-by-task basis.

So - if you have a feature you really want to see happen, that you really think is important we tackle and address, your options include:

• Do it yourself - the code is there and we dont bite when it comes to new contributions. (Just as long as the code matches our other guidelines about quality, modularity, etc.)
• Convince someone to do it for you - this it the hardest of the options since we’re already very busy as a group, but it’s certainly possible. Make a convincing argument - it helps if you can research it and break it down into specific tasks. (”Improve stability” is not a task - “Fix crashes when/while XYZ happens” is.)
• Hire someone to do it for you - it’s an option on the table too. There’s a lot of developers familiar with the codebase now, lots of them are looking for beer money and can implement your pet project or ideas for a fee.

So in conclusion - if you have something you really think is important, really want to see - think it through, ask yourself “Is this more important than what people are working on already”, “Is this something that OpenSim is ready to support”, “Is this important enough that I am willing to work to see it done?”, and finally “If no-one thinks it’s that important, ready or <insert reason here>, am I willing to pay to see it happen?”. Because at the end of the day, features take time, and time is a non-renewable resource - people like to see it invested wisely.

We’ve got a couple of tickets available for people who can help us explain OpenSim to conference attendees in our very-spacious booth being sponsored by DeepThink, Genkii, RealXtend, SineWave and ISID.

If you want to get a free pass to attend in return for helping us out:

• You must know your stuff - you must be a regular user of OpenSim and/or RealXtend, ideally hanging on the IRC channels or reading the mailing lists too.
• Be prepared to spend at least a couple of hours in our booth (you don’t have to stay for the whole time)

If you are interested - send me an email or leave a comment where I can contact you. We’ve got a number of free passes so the more the merrier.

This one comes up a lot - I hear it in quite a few places “Well, shame it’s in C#.”, it’s usually followed by some nebulous statement about Microsoft, followed by patent threats, embrace extend extinguish, etc etc.

So let’s start with the basics -

• C# is a ECMA and ISO standardized language. It went through the review procedures of ECMA and ISO in a standard fashion (unlike OOXML). Download the ECMA Spec here and the ISO Spec here.
• Yes, the base library is included in that standardization. The primary exceptions are, ADO.NET, ASP.NET, Web Services and Win Forms. Many of these exceptions are however separately covered via Microsoft’s Open Standards Patent program, although we’ve moved to avoiding them entirely in the standard release. (Extensions which use them are however available on the third-party utilities forge)
• The ECMA standard also includes the CIL byte code format.
• If Microsoft decide to add new extensions onto .NET (which they have done with every major release), the OpenSim developers are content to wait until those extensions are available under Mono (which moves fast enough that it isn’t a major problem).
• Microsoft is not known for breaking backwards compatibility to “extinguish” things - the mere fact you can still run Win3.1 applications on Windows Vista should give some assurances there. Microsoft is yet to make any kind of retroactive change to the .NET standard - all .NET 1.1 applications should still run under .NET 3.5 without changes. (and the cost to them of making a change like that would be significant in terms of people using applications under Windows)
• There are two completely F/OSS implementations of C#/.NET and the standard library. Mono (Licensing Concerns Addressed Here) and the FSF’s DotGNU PNET. OpenSim is regularly tested for compatibility under Mono (in fact our automated testing environment uses it). DotGNU is significantly less popular and has not been properly tested with due to not being feature complete yet. There is also a third source-availible implementation from Microsoft called Rotor, however it is not under a OSI-approved license.
• Microsoft maintains a reasonably healthy relationship with the Mono developers and has been known to collaborate in the past (such as for the development of the specialised Moonlight runtime).

The next question usually is “Well, why not write it in Java then?” the answer is multi pronged and highly likely to generate a flame war on the subject - the biggest reason is that coding the same thing in Java would probably take significantly longer to do.

Java is a beast of a language that has had layers of gunk added in every revision resulting in a hodge-podge of inconsistently named items in the standard library that may, or may not address what you want. The second major reason is that the C# standard library is both larger and more functional - the amount of time and effort the Base Class Library has saved is astonishing. Wikipedia has a nice article detailing the differences between the two languages.

However, since both Java and C# share a very similar byte code language - it is possible to do a machine driven cross-compilation so you could run OpenSim under the JVM runtime if you so wish. Source translation between the languages is also reasonably possible however requires a degree of manual work.

Some concluding facts which may actually surprise some people

• One of the largest contributors and users of the project is IBM. One of the first groups inside of IBM to get involved was IBM’s Linux Technology Center. All[?] of the IBM developers are using Linux, Emacs and Mono to develop and test.
• Approximately half the developers working on OpenSim are running under Linux/BSD. As a user base, Linux users represent approximately 80-90% of the casual testers and operators. (Windows is however much better represented in people running commercial operations)
• Our compatibility targets are Mono 1.2.5 (latest is 1.9) and .NET 2.0 - we dont use features which supercede these (although we may raise that to Mono 2.0 once it is out of beta).

What this competition is about

For the upcoming Virtual Worlds 2008 conference in LA, myself and some of the other OpenSim contributors and developers have decided to sponsor a large booth, and we’d like to cover it with screen shots of the best and most innovative uses of OpenSim out there today.

What we need

We need high resolution screen shots from your builds, ideally these should be captured at a minimum of 1600×1200 pixels (if you are using the Second Life™ viewer, the “High Resolution Screen shots” option works well). All settings should be set to maximum, ideally with anti aliasing, screen shots should have a minimal amount of adjustment (limited to cropping, brightness) and originals should be provided.

The Specifics

• High Resolution - We’re printing onto a 300 DPI surface, this means we absolutely need the highest possible resolution when printing to make sure we have crisp clean non-blurry images. While there isnt a definition of what is or isnt high resolution - try submit screenshots at least 1600×1200, higher is preferred.
• Submit in a lossless format - We need images provided in either 24-bit PNG, TIFF or BMP. As these files tend to be rather large, please zip or rar them with maximum compression.
• If you are submitting a manipulated image, the original is required as well. There is no guarantee that the manipulated version will be used. (We are trying to provide accurate but nifty portrayals of what OpenSim can do.)
• Deadline - submit your images before Wednesday, 27th August 2008. Sooner is appreciated as we will begin incorporating images into the layout as soon as they are received.
• How to submit images - Please use a service such as yousendit.com to transfer the archived files, send your message to “adam@deepthink.com.au”. My inbox will reject files larger than 10mb, so please do not send these directly.
• Judging will be done by myself in conjunction with the other people sponsoring the booth. Decisions whether to utilize an image will be based on constraints such as whether or not we can work them into the larger montage and do so in a way which highlights OpenSim in a positive way.
• Some tips - People/avatars always look good. Eye candy is always a plus. Showing scenes where this is in production and potentially useful for people interested in using it are also going to be in demand.

What you get?

Accepted and utilized images will get 6 months free standard-class region hosting from DeepThink to a grid of your choice. The Judges may provide hosting for images of excellent quality which are unable to be used, however this is soley at the discretion of the judges.

Every now and then, this hits me. I fire up OpenSim (or RealXtend), and it crashes instantly with a “BadImageFormatException” - when you see this, you know you have a compatibility problem with an embedded C/C++ binary. In english, 90% of the time this means you are running under a 64-bit environment with a mix of 64 and 32bit code trying to run together.

OpenSim is 64-bit aware

The reason for this happening is that OpenSim by virtue of the .NET platform is quite 64-bit aware, this means natively it can address 16TB of memory just fine if run on a 64-bit operating system. (nb, under Mono you need to make sure Mono is 64bit to get the same benefits).

However unfortunately, some of the libraries we link against have to be compiled ‘one way’ or the ‘other way’ and not both.  When running a 64-bit application, things such as memory pointer lengths are difference, so there is no way to cleanly pass data between a 32-bit and 64bit application - everything must be one or the other.

So how do you fix this?

There’s two routes, the easy route, and the proper route. The easy route is good for 90% of our users - if you dont need to access more than 4GB of memory and dont mind about the slight slowdown when handling double precision numbers, then just run 32-bit.

How? Instead of launching OpenSim.exe launch OpenSim.32BitLaunch.exe instead - this forces OpenSim to run under a 32bit environment (under windows provided by WoW32).

The more detailed fix

The next option is to strip out the sections that are causing problems. OpenSim is modular - so you can swap bits and pieces with their alternatives. The following are components that are not 64-bit compatible by default (however it is possible to fix this, something I will get to in a moment.)

Incompatible Components List

Physics - most problems come from our Physics Engines, since these tend to be written in high performance C/C++ with ASM littered. The following list of physics engines by default are NOT 64-bit compatible.

• OpenDynamicsEngine - The ODE DLL we provide is compiled for a 32bit operating system, however you can fetch the sources for our custom ODE DLL from (SVN) http://opensimulator.org/svn/opensim-libs/ and build it yourself on your native environment.
• AGEIA PhysX - The AGEIA PhysX support (now Nvidia PhysX) relies on a natively compiled 32-bit DLL. At present there is no fix here.

Compatible Engines

• BasicPhysics - This is purely managed but very simple in operation. Collisions are provided only between the avatar and the ground here. This runs without problems regardless of environment
• POSPhysics - POS physics is a more complicated BasicPhysics engine with bounding box collisions between objects. For some tasks this is sufficient.
• BulletX - Our own custom BulletX library is derived from the BulletXNA project, this is a properly developed fully managed physics engine that does proper collisions (however the friction coefficient can be a little low for some users).

Storage Engines - At least one of our storage engines relies on some hard coded components, it’s listed below

• SQLite - Whaaa? SQLite is broken on 64-bit environments? Afraid it’s true. Unfortunately on Windows systems the only solution is to recompile the entire of Mono (including Mono.SQLite.dll) yourself under a 64-bit flag.

Compatible Engines

• MySQL - The DotNetConnector provided by MySQL is 100% compatible and probably the recommended adapter for production installs.
• MSSQL - Windows-only however MSSQL is also free and the adapter is built into .NET itself so is pretty much guarunteed compatible.

Other incompatible components

Perenially we have problems with the following components in addition to the above, this includes libsecondlife’s OpenJPEG version - this can be fixed by compiling libsecondlife and OpenJpeg (using make) on the target system. This may have been fixed recently however as complaints about this DLL have lessened sharply.

Running

Once you have swapped incompatible components out, or recompiled them appropriately, OpenSim should run under a 64-bit environment natively on Windows. As mentioned above, under Linux/Mono you will need to make sure that Mono has been compiled as a 64bit application for this to take effect.

The differences between the two are mostly marginal, however there are some definitve improvements in certain mathematical loops and stability when using large amounts of memory. In production environments, running 64-bit mode can be an attractive option, however will require constant maintainence to compile the above libraries as new releases occur.