[ODE] AMotor question

[Bill]

Back in the days of Atari, they didn't have ODE. They had animations for 
rotations, boxes for collisions, and vectors for controlling the 
"physical simuation" of each sprite. 2 vectors, 1 for position, and 
another for the velocity. The rotation is just an animation, since 
rotating a sprite is costly CPU-wise. Collisions with bullets are 
handled with simple boxes. I'm sure you can do all that yourself in 
under 20 minutes.

Oh, BTW, they didn't actually use vector math. I don't think Atari had 
floating point math ;) so it'd have to be done in an integer way, rise 
over run. Precomputed of course. But since we have plenty of CPU and 
fancy C/C++ you can use vectors for easy math.

~Bill

Terence Lewis wrote:

>Hi,
>
>First, although it's a bit late, I'd like to say
>thanks for the timely responses to my last question to
>the list (about 4-6 weeks ago already?).
>
>Now, I have a couple of new questions :). First,
>looking back through the archives (a painful process
>in notepad), I've seen this question asked, but
>haven't been able to find an answer. I need to attach
>an AMotor to a single body. I.e, between the body and
>the world.
>
>The reason is as follows. I'm writing a 2D game, an
>aircraft game, like the old 1942 games for the Atari.
>I'm not interested in a realistic physical simulation,
>I want speed and an easy to use collision detection
>library.
>
>Now, the problem I'm having is that when my plane
>moves left or right, I'd like to have it bank. So I
>added a torque around the y-axis, and everything was
>fine, until the plane flew upside down, and then
>continued rotating around.
>
>So, for a while, I threw ODE away for this type of
>situation (using a flag to use ODE for position, but
>not for Rotation). I wrote an interpolator to change
>the correct Euler angle for the rotation I wanted, and
>got a constant angular velocity, until I hit a maximum
>rotation around the Y-Axis, which I could specify.
>
>However, this approach always felt like a 'cheap hack'
>to me, and I'd like to go back to using ODE. So I read
>through the user guide and found a section on angular
>motors that seem to have just what I need. I can
>specify maximum and minimum positions for rotation
>around the Y-Axis, and ODE will handle the rest for
>me.
>
>However, I get an assert when I attempt to add this
>motor, because I'm trying to attach it to the world,
>which the manual says is possible (or at least, the
>manual isn't clear on which joints/motors need two
>bodies).
>
>Also, currently, when the user presses say, the up
>arrow, I'm adding a force in the plane's relative
>y-direction, to provide some acceleration. I see in
>the manual however, that direct application of forces
>isn't a good idea, and so I'd like to know if I can
>use slider's for this? Again, they'd need to be
>attached to only one body. 
>
>I'd like to try this approach, because I'm not
>impressed with the handling of the plane at present,
>and I believe being able to set the velocity to zero
>in one time-step (when the user releases the up-arrow)
>will provide me with much better (though I admit far
>from realistic) handling.
>
>The next question I have is in regards to timestep. As
>this is a game that needs to run in realtime, I find
>that large fluctuations in framerate can cause certain
>weapons (projectiles fired from the player's ship) to
>misbehave.
>
>I've got a weapon that works fine when there's not too
>many enemies in the game, but the second there's more
>than about 5, it suddenly manages to disappear. I
>presume it's being given a large velocity and is being
>driven off the top of the screen between time-steps.
>
>Can anybody provide suggestions to get around this? Is
>it very bad to run the physics in non-constant
>timesteps? If so, does anyone know how I can run at
>fixed intervals in a game, and still keep graphics and
>physics synchronised? 
>
>I've tried StepFast1 as well, but I'm not sure yet if
>this alleviates the problem (I changed the level file
>so that there's not so many enemies at once).
>
>My last question is in regards to the archives. I've
>had much trouble trying to browse through the old
>posts because I'm using Notepad. I read in one of the
>posts that Netscape can read the format and
>significantly enhance the output. Is this true? Do I
>need anything special for Netscape, like some kind of
>plug-in, or will it just work as is if I download it
>(Netscape 7.1, full install).
>
>Thanks for taking the time to read this rather
>long-winded post, and I'd appreciate any help
>regarding any of the questions I've posed.
>
>Thanks
>
>$£¥
>
>=====
>We scratch, our eternal itch
>A twentieth century bitch
>And we are grateful for
>Our Iron Lung
>
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