Posts Tagged 'physics'

Relativistic lattice

How would the space look like if you were going really fast? You could find some videos if you know the key words, but not enough interactive stuff, so here goes one:

development screenshot Continue reading ‘Relativistic lattice’

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Gyroscope adventure

In case you can’t fully understand yet what Adobe means by focusing on (desktop) gaming and video and not general purpose apps, allow me to demonstrate. Suppose you are making mobile app and for whatever reason you want to track device orientation. How hard can that be? Check it out:

Apple way

If you’re native iOS app developer, you are dealing with ecosystem that does support general purpose apps. You have simple CMDeviceMotion class that performs sensor data fusion, filtering, bias removal, etc, and gives you orientation data in any form you want (roll + pitch + yaw, or matrix, or quaternion). Case closed. The same class conveniently splits accelerometer data into gravity and user applied acceleration, btw. In a word, it’s perfect.

Adobe way

If you’re AIR app developer, prepare yourself – you’re going on the adventure. You can start by looking at flash.sensors package – for some mysterious reason, it has accelerometer API for desktop, but no gyroscope API for mobile. Why? Because Adobe does not feel obliged to include every piece of code you might think of in their runtime. But don’t give up your hope yet – Adobe has the solution for this kind of problems – AIR native extensions. And, it turns out that Adobe made one for you to access gyroscope data. Despite of being abandoned in 2011, apparently just before Adobe’s focus shift kicked in, this ANE still works with current AIR 3.x.

Okay, this is the part where you’re happy that you don’t have to write ANE yourself, and it seems that getting your hands on device orientation data is now only a matter of few additional build settings. Well…

This extension API, designed to be Accelerometer class twin, has two major problems in the way. Number one is that it only exposes raw gyroscope data, i.e. rotation rate. Since this is not something that flash developers do every day, you probably have no idea how to go from radians per second to orientation quaternion, or transformation matrix. So to use this ANE, you will have to learn some new tricks, such as finding approximate differential equation solutions, Taylor expansion of matrix functions, series summation and evaluating indeterminate forms. If you are still with me, good guy Oliver J. Woodman will guide you through this hell (pages 21 to 23).

Ok, now you’re done reading that and ready for action, right? Not so fast – there is problem number two. Let me just quote this comment from ANE source code:

// The singleton ExtensionContext object listens for StatusEvent events that
// the native implementation dispatches. These events contain the device’s
// gyroscope x,y,z data.
//
// However, each Gyroscope instance has its own interval timer. When the timer
// expires, the Gyroscope instance dispatches a GyroscopeEvent that contains
// the current x,y,z data.

Thank you, Adobe engineer, for this brilliant idea. Because there just can’t be enough lag or noise in my data. Sigh… so what do you do about this? You bypass ANE AS3 wrapper, and access its internal methods over low level interface. Of course, this means that you have to study both wrapper and native code beforehand :(

And here, my friend, we come to the end of our wonderful journey. I will go back to work on my AIR app, and you will maybe go and write your own ANE, with blackjack and hookers. Or you may choose to continue where I left off – maybe add Kalman filter or something. And don’t forget to write back, if you do :)

Convex hulls

What kind of freak would code things on Dec 31st? That’s right, it’s me.

So. Suppose you are making a game using 3D engine for graphics and 2D engine for physics (that uses convex shapes only). So, most probably, you would need to project your model onto your physics plane, find convex hull of resulting points set and create corresponding shape from that. Since today (rev 891 I think) you have one part of this done for you by sandy, namely 2D convex hull.

Check it out, and see ya’all in 2009.

Physics in Alternativa3D

This little experiment explores possibilities of Alternativa3D engine to simulate physics.

This is probably the simplest thing one could do – bouncing ball. Also, I have added previously developed custom sprite and light materials – you’re going to need them in case you plan to mess with sources. Continue reading ‘Physics in Alternativa3D’


Old stuff

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