I spent some time the past few weeks tinkering on the GPGPU framework to make it a bit more flexible and more robust. First of all, it got renamed to the acronym Sage (Simple Abstraction for GPU-based Evaluation), mainly so I don't have to type simple GPGPU framework all the time. The main goal of the recent developments was to support the usecases presented by Navier-Stokes fluid simulation as implemented by Epsicode. After quite a bit of pondering and redesign we managed to get it to run 100% on the GPU and I have to say the result looks absolutely stunning:

The main change here is that since this simulation deals exclusively with texture output, the data isn't needed on the CPU at all and the data and computations can remain solely on the GPU. The update to 0.3 turned out to be lacking in terms of flexibility to support this properly and truth be told the GPUBufferUsage.PassThrough flag was far from intuitive. With the upcoming version of the GPGPU framework this will be addressed by having GPUBuffers own their GPU resources, instead of borrowing them from the GPUProcessor. This makes GPUBufferUsage.PassThrough more straightforward, since it's more obvious that a buffer with this flag set will be using its own RT when asked for input, instead of using some RT internal to the GPUProcessor. Perhaps renaming GPUBufferUsage.PassThrough to GPUBufferUsage.UseOutputAsInput would be even more obvious, but it just doesn't sound as mysterious :)

Another change to the GPUBuffer is that the output (the owned RenderTarget) can now be double-buffered. That means that a GPUBuffer can be set as both input and output (texture and RT) simultaneously, while the system transparently takes care of the details. With the help of the excellent 3rd party support by MS, these changes mean the data doesn't need to come back to the CPU at all, which can drastically improve performance. When we started porting the fluid simulation over to Sage we were happy to have it running on a grid of 64x64 data points. With this upcoming version of sage, it can simulate a 512x512 grid smoothly in (mid-to-high end) SM3 hardware and reportedly simulates a 256x256 grid at a leisurely 60fps on the 360.

At the moment the development focus is on migrating the framework into a library project of its own (for easier maintenance and upgrading) and reviewing the design of the new features, to make sure there aren't any gotcha's like GPUBufferUsage.PassThrough in the upcoming release. The samples from the earlier releases will also be ported over and added to the solution. With some more fancy features in the works I don't have a particular release date in mind just yet, so if anyone should want a 'CTP release' in the meantime just drop me an e-mail to feedback@xnainfo.com.

There seem to be a lot of exciting things happening at the moment. XNA 4.0 has been announced which adds Windows Mobile 7 phones to the list of supported platforms, but you already knew that of course. While Shawn is busy at GDC, I took the liberty of stealing his Fractals code. It doesn't improve anything upon his release in 2006, but I happened upon it and I thought I'd be nice to have this available as a ready-to-run sample. On that page you'll also find my take at handling input (inspired by this discussion) which seems to be all the rage these days.

Other than that, I've started tinkering on a little animation pipeline for XNA together with a 3D artist as a learning experience. I have no idea if this will be anywhere near finished any time soon, or if it'd even be useful for the community since there seem to be a lot of libraries out there already. Like any good software project I settled on an acronym for the name anyway before its anywhere near done, so I lay claim to Uxmal. It's a good fit since the artist is working in Maya and I'm on my third rewrite of the codebase already. Xna Model Animation Library also fits, but my development efforts are currently stumped by trying to come up with what the U should mean. Useful would be ideal, but it might also be Unnecessary or Useless.

Time will tell :)

  
I really gotta stop doing things like this. What started out as a Soft Body Physics demo ended up in writing a barebones GPGPU library, which ended up in writing a stand-alone GPU-particle demo for release on XnaInfo (coming soon!), which ended up in a little black hole:

I hope to find some time for the write-ups and posting code soon, please bear with me :)

I've been working on a soft body physics demo (more details). I haven't had time to write up more about it to post here, but I wanted to try to see if posting YouTube videos works on this infernal blog software. Stay tuned for more on this :)

I came across an excellent discussion of setting up a logarithmic depth buffer in Cameni's Journal. I heard of those before, but I was surprised to find implementing them is as easy as adding only one simple line of code to your vertex shader:

output.Position.z = log(C*output.Position.z + 1) / log(C*Far + 1) * output.Position.w;

The C constant allows you to define the resolution you want at the near plane and Far is the value you use for the far plane. More details can be found in the journal linked above. I happened to be tinkering on a model of our solar system with a bunch of stars surrounding us (from Hipparcos data) to scale. The lightyear distances for the stars and the AU distances within the system were a source of woes with the depth buffer, but using this simple line made my z-fighting stars play nice.

I haven't gotten around to writing interesting samples or uncovering any deep XNA truths lately. Instead I've been tinkering on a little beat-em-up game with stylized stick men to do the fighting. These little actors are entirely procedural, so the game itself generates the geometry and animations rather than using models created by artists. Obviously nothing can replace a good artist and this proved painfully true when it came to the animations.

The animations are generated by a particle-based physics system (described here), which works by applying force to the attacking limb towards the victim, checking collisions and letting the simulation run its course. The base skeleton displayed below is set up easily enough, but without additional contraints the resulting movements are far from natural. As noted in the original article, a lot of tweaking can also be done using the mass of particles to get some control over how easily particles (i.e. joints) can move.

So if the skeleton and animations are that hard to tweak, you might be wondering what good this procedural technique is then. The beauty of this -admittedly simple- physics based rendering setup is that you essentially get inverse kinematics for free. If I want to hit my opponent with a hand, I just apply some force on the hand towards where I want to hit him. With sufficient tweaking, this produces convincing animations for accurately hitting the victim anywhere with any part of the attacking actor. Headbutts, kicks and more exotic attacks are just a matter of picking target and subject particles on either side.

Another nice benefit of this procedural approach is that the geometry is very accessibly to the program and thus can be altered in a variety of ways. With a few minutes of tinkering, style variations like those below are easily implemented.

The project is still a pretty long way off from becoming a playable game, but it's already made its way around the office for passive-aggressive stress relief   I'm afraid I can't put a playable build out anytime soon, but in the meantime here's a little movie (WMV, 7mb) showing some basic pummeling and the style so far. Since a lot of tweaking is involved and much of the style is still up in the air, comments and/or suggestions would be much appreciated.

A bit of an off-topic post for any Dutch readers that may come across our little blog. MS decided to revamp their Dutch .NET Magazine and change the subscription to Opt-In, meaning you'll explicitly need to tell them you want to keep receiving the magazine after the next issue of September 22nd. You can find more details and re-subscribe over at this page:

http://www.microsoft.nl/netjesgeregeld

It's quite a risky step for them to take, but they want to make sure they're reaching their reader base and get a clearer picture of the interests of their readers. The magazine remains free and they've drummed up a full-blown redactional team for the revamp, so if you've enjoyed the magazine so far make sure you re-subscribe!

Since the stuff I'm working on for XNAInfo is taking forever to finish, I thought I'd post a link to this little gem here in the meantime. On my forum rounds I find myself linking to Tom's Excellent DirectX Faq at least once a week. Obviously it's DirectX specific, but that easily translates to tons of useful information on XNA development on Windows. It's a great resource that should prove useful for just about anyone.

(Sorry if this pops up twice in your RSS reader, something was off with the publishing) 

Some time ago a topic popped up on GameDev on how to stick a WebBrowser control on a D3D surface, or rather an XNA texture level. After some tinkering we got it to work (obviously Windows only), so it can be used to render any webpage to an XNA texture. The next step was to try and make it interactive, paving the way for HTML and Flash based GUIs. Unfortunately we ran into a strange bug here, which I haven't been able to solve. So I figured I'd post this out here, hoping anyone comes across this who can help out.

Here are the (messy) demo projects:

• Original browser-to-texture code (useful if you're just looking to draw HTML in XNA)
   
• Threaded interactive browser on texture
  

The bug surfaces in the 2nd project. Basically it works fine until the user left-clicks anywhere on the control (doesn't have to be a link), after which WebBrowser.DrawToBitmap fails silently and only an empty white bitmap gets rendered. The strange thing is that the WebBrowser control does load the new webpage. By uncommenting line 241, mouse moves are posted to the control and the window title will show the HREF of links on the (loaded but invisible) page as you hover over them.

Anyway, perhaps someone better versed in window messages can check this out, see if the code for posting mouse presses/releases is correct. While researching this problem, I also came across this MSDN page which states DrawToBitmap isn't supported for the WebBrowser control anyway, so it seems a miracle it works in the first place. If anyone cares to comment on that, please let's hear it.

Having just been badly upstaged by MJP's post, I reckon this might not be too interesting except for a few RTS/AI enthusiasts. Anyway...

In a recent discussion on RTS AI, Matias Goldberg pointed out the quite ancient text The Art of War by Sun Tzu. Since I've been fostering an RTS pet project for years now, I decided to get a copy and it turned out the best $4.95 I probably ever spent (ISBN10 0-486-42557-6).

Obviously it's not a cookbook for writing RTS strategies, but after a first read I can definitely see how various stratagems and axioms could be used to construct a clever AI. In fact, I'm amazed how many clear cut rules of thumb Sun Tzu puts forward that could be readily applied. These however may only serve to highlight the limited scale on which popular RTS games play out.

Food for thought at any rate.