## Strange velocity bug.

If you have problems installing or running Algodoo, have found a bug or need in-game help - this is it!

### Strange velocity bug.

If the velocity values [x,y] are manually entered into ANY object which is glued to the background, then ALL other objects which are glued to the background will receive that entered value! Also, any non-glued object will propel off any glued object with a velocity that equals the entered velocity value!

See my example scene: Strange Velocity Bug

Xray

Posts: 499
Joined: Sun Jun 17, 2012 6:12 am
Location: USA

### Re: Strange velocity bug.

The cause for this bug is the fact that all glued objects, including things like planes, share the same body group. If you enter a velocity into any of them however, then algodoo assumes that velocity for the entire body group during physics calculations, and since fixed bodies can't have their velocity changed, this velocity becomes permanent. Since glued objects however are strictly prohibited from moving, they still remain in place despite this. The consequence is that every collision with a glued object behaves as if the glued object was moving with the specified velocity, thus transferring a part of that velocity onto the colliding object.
FRA32

Posts: 227
Joined: Wed Dec 03, 2014 9:51 pm

### Re: Strange velocity bug.

Hi FRA32!

I agree. Your explanation seems completely reasonable.

You said: "Since glued objects however are strictly prohibited from moving..."
Well, that is only partially correct. Objects that are glued to the background cannot move by changing their velocity vectors, but they CAN move by changing their POS values (I'm not sure if Algodoo X and Y POS values are considered scalars or vectors).

Thanks for your explanation. It was very helpful!

Xray

Posts: 499
Joined: Sun Jun 17, 2012 6:12 am
Location: USA

### Re: Strange velocity bug.

Well that obviously depends on what your definition of "moving" is. I would define overwriting the POS as less moving, more teleporting, but in the end, isn't movement in a computer program nothing but the perpetual teleportation of objects in tiny increments?

Also, I am pretty sure the POS in thyme itself is stored as a mere array filled with 2 floating-point-numbers. The Algodoo software then interprets those values and puts them into yet another array as part of a "Vector2D" class of sorts for mathematical purposes.
FRA32

Posts: 227
Joined: Wed Dec 03, 2014 9:51 pm

### Re: Strange velocity bug.

Yeah, the term "moving" can be defined multiple ways in Algodoo. Obviously objects in Algodoo do not behave like real world objects. They can be made to do all kinds of magical things that defy our normal laws of physics. That's what makes programming so much fun!

Xray

Posts: 499
Joined: Sun Jun 17, 2012 6:12 am
Location: USA

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