Blender Scale and GGJ

Some more notes on blender. Scaling and dimensions seem to have a strange relationship. To actually modify the dimensions of an object bring up the transform properties ('N') and then press CTRL-A to apply the magic once your done. Weird.

I also revisited the best of global game jam after a gamasutra article on the jam and to my very surprise, zeppelin escape got a comment of being a good game, and when i checked out the leaderboard, were the 10th best game! wow!

Filtering noise

The robotics project I'm working on suffers from some very noisy sensors. A simple 1st order low pass filter doesn't do the trick. The noise has a low frequency cyclic component as well as standard white noise, plus occasional electrical spikes. It's not great.

We tried a number of things including 2nd order filters, bandpass filtering (to try and remove the low frequncy cycle), fuzzy sets and more.

I was hoping to avoid a Kalman filter style approch (since they are painfull to formulate, and they are only meant to handle gausian noise as far as I know). H-infinity filters are another option, (which can handle non-gausian noise and don't require a complete system model) but they are still too complex for my liking.

So we settled on trying an Alpha-Beta filter since that should give a vauge idea of how the Kalman might act, and its looking promising.

I'd never heard of these before, so thank you wikipedia! I'll have to spread the good word.

Physics Engines

Whilst reading Cesar's blog I realised that Pixelux's very impressive physics engine is finally available commercially under a indy license.

Other physics engines that have recently come onto the scene are Virtual Physics (a research physics engine) and Algoryx (a commercial simulation physics engine).

There is also SOFA, not sure what that's all about yet...

PAL evaluation - evaluated

Found a nice post evaluating my evaluation of PAL. Evaluating Physics Engines For Games - PAL.

I'm working with Evan author of Physsim on a more indepth analysis of some of the collision cases in the paper. What a timely post.

Smoothed Particle Hydrodynamics on the GPU

I've been working together with Neil Osbourne on a GPU version of my SPH code. He tried a number of things and managed to get a significant speedup. He presented his results at the iVEC eResearch Forum 2009. Main lessons learnt were to keep the number of CUDA threads approx equal to the number of hardware processors, not to do memory optimizations too early on, and ofcourse, to do shared memory optimizations later on.

Never managed to get a hashed grid going within the time we had, but it was still a cool project. With a bit more effort it should find it's way into PAL or Bullet.

New stuff

So I finially get my internet access back after loosing it for almost a week. Yay.

Did a quick look around to see whats new online, there is a "next-gen" open source COLLADA import/export plug in being developed for MAX and Maya . Sony is involved in the development again.

Whilst on the topic of Sony, apparently Intel is developing the next GPU for the PS4, so no doubt this will be larrabee based. Intel seems to be driving this hard, and since they have about 40% of the GPU market this could get interesting. Especially now that nVidia is picking up x86 engineers as well apparently. So perhaps the new GPU standard will be x86 based GPU's similar to Larabee. AMD/ATI, Intel already have the know-how and nVidia seem to be acquiring it. Why anyone wants to do this is still beyond me.. x86 is cluttered enough as it is...

Blender Physics Links

More on links..

you might want to make things look nicer, or at least have something to indicate the difference between convex/meshed objects and 'physics objects', you can make things look nice by applying a material, and going into the edit mode (after, view,select,object) you should see a mode selector. Then select mesh->faces->set smooth. Press ctrl-alt-numpad0 to realign a camera for rendering. Set the background color in the shading section in the materials mode. F12 to render, F3 to save the render.

You can set link's pivots and axis's. A hinge rotates about its own X axis. The Axyz are set in degrees.

Using generic constrains is a bit funny, if you want a constraint to be active, you need to click on it. (eg LinMinX) and that will stop it from allowing movement (if min and max == 0), otherwise type in the value you want to have constrainted.

For the time being, you can get a great chapter on blenders game physics here:
http://www.cs.brandeis.edu/~tim/Classes/Spr09/usem2c/readings/Ch6.pdf

Unfortunately the COLLADA constraints continue to be plauged by issues, you can't export them as individually enabled/disabled, and the only physics engine that supports the COLLADA link format is Bullet.

Forces/controllers don't export to COLLADA either, so that is all lost too. *sigh*

Blender

Blender has to be one of the hardest packages to use. I don't know why they defy convention and don't let you select objects by CLICKING ON THEM. Although recent versions fix this somewhat by defaulting to object-mode and letting you right click to select. *sigh*.

Using blender for physics is somewhat convenient due to how closely blender follows the physics&COLLADA conventions.

Beginer notes: hold MMB to rotate view, scroll to zoom, shift MMB to pan. on a selected object, "s" will scale, "r" will rotate. ALT-r will clear rotation. translate things by clicking on the relevant axis.
(You can press 'N' to get the transform properties and type in locations. handy!)

To create a physical object, select it (object mode, right click ;)) , go to the logic pannel (F4) make it an dynamic actor, and rigid body.


To create the correct physics shape, select 'Bounds' and change to (eg: box/sphere/convex)

Press 'p' to preview. (ESC to exit the preview)

To add a material, swap to shading mode (F5)
In link to object, delete anything you might see (eg: MA.Material.001) and now you can create your own materials. In the material tab, press the DYN button so you can set friction and restitution.

(you may wish to create another object before trying links, eg: add->mesh->sphere)
To add a physics link or rigid body constraint switch to object mode (F7).
To create a link press the add constraint button and choose Rigid Body Constraint, then choose type (eg: Ball) and which object you are connecting to (eg: "toObject:Cube"). P to preview your swinging cube!


Some tutorial links:
getting started with blender physics & COLLADA.
some info on controllers and physics materials
basics of controllers
global/local forces and more on controllers

Game hardware stats

It's always usefull to know the hardware stats of the big wide world for your next game.
The steam survey is usefull for top-end or "hard-core" "gamer" PC's
Whereas the unity stats tell you more about the casual market.

I'm suprised that so many people have DX10 capable GPU's.

Global Game Jam

The global game jam was on the weekend, and I spent the days there making a game Zeppelin Escape.
There isn't much time in 48 hours, and we were learning Unity, and trying to avoid the beta bugs, so it was an interesting experience. We couldn't figure out how to get Unity's collision code going so I wrote it again from scratch, as well as doing the "AI" for the enemies, movement system, and 'designing' level 2 & 3.

There were about 25 people there and all round a great time was had. Highly recommended.