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How to make continuous rotation ?


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#1 ryt   Members   -  Reputation: 294

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Posted 28 October 2013 - 01:24 PM

I have a rotation:

 

rotation = Quaternion.AngleAxis(45, Vector3.right);

rotation *= Quaternion.AngleAxis(5*Time.deltaTime, Vector3.up);

 

where "rotation" is a quaternion and angle is in degrees.

 

This rotation does not rotate, but instead it stands still. This is because Time.deltaTime is small value and it doesn't increase.

We could make the angle of 5 increase or make Time.deltaTime into Time.time. This way we would get an object always rotating around Vector3.up.

 

The first line rotates around global coord system and it must be the first one.

I really don't want to use Time.time, so I don't know how to transform this rotation to use Time.deltaTime.

 



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#2 Nypyren   Crossbones+   -  Reputation: 3646

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Posted 28 October 2013 - 01:30 PM

Keep a "rotationAngle" variable at class scope and increment it by the desired angle*deltatime once per frame.


Edited by Nypyren, 28 October 2013 - 01:31 PM.


#3 ryt   Members   -  Reputation: 294

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Posted 28 October 2013 - 02:24 PM

This way I would get the same as Time.time.

I thought maybe doing it like:

 

rotation = Quaternion.AngleAxis(45, Vector3.right) * rotation;

rotation *= Quaternion.AngleAxis(5*Time.deltaTime, Vector3.up);

 

but that wont work.



#4 Madhed   Crossbones+   -  Reputation: 2452

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Posted 28 October 2013 - 02:46 PM


rotation = Quaternion.AngleAxis(45, Vector3.right) 

 

This line always resets the rotation so you will of course get *almost* the same rotation every frame.

What Nypyren wrote is right: Increment a counter and use that instead of deltatime.


Edited by Madhed, 28 October 2013 - 02:47 PM.


#5 Nypyren   Crossbones+   -  Reputation: 3646

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Posted 28 October 2013 - 09:12 PM

This way I would get the same as Time.time.


You'll get a value which seems similar to Time.time, but you have much more control:

- You can control the rotation with the keyboard. For example, rotate left if the left arrow is pressed or rotate right if the right arrow is pressed.
- You can keep track of different rotations for different objects.
- If your game pauses but Time.time continues, you can pause your rotation without it jumping ahead when you unpause.

#6 Paradigm Shifter   Crossbones+   -  Reputation: 5094

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Posted 28 October 2013 - 09:25 PM

You should have 2 clocks anyway... real time and virtual time, the real time clock keeps ticking when the game is paused. Virtual time only runs when game is running and you can scale it for time control effects too.

 

If OP is worried about accuracy with a constantly increasing time you can use fmodf to do a floating point modulo style operation so values wrap around at multiples of the periodicity, or just subtract the periodicity when the counter overflows.

 

EDIT: I also saw an article or blog from a guy a Valve who says they use double precision time but start off at a large value so it keeps the same precision for a long time (something like weeks or months, maybe years), but my google fu failed me.

 

EDIT2: Google fu didn't fail me for long, when I remembered it was in a blog post! http://www.altdevblogaday.com/2012/02/05/dont-store-that-in-a-float/

 

EDIT3: I'm sure there was something in the blog about starting the time not at zero but I guess I misremembered. Maybe that was in another article in his discussion of floating point stuff, so check the other articles as well.


Edited by Paradigm Shifter, 28 October 2013 - 09:35 PM.

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#7 ryt   Members   -  Reputation: 294

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Posted 30 October 2013 - 11:23 AM

I think you misunderstood, probably I should gave more information, sorry for that but thx for your replies.

I was looking for continuous rotation, the rotation I wrote it stands still, not by changing time variables.

 

I found the solution and the two lines just need to be replaced with one another.

 

rotation *= Quaternion.AngleAxis(5*Time.deltaTime, Vector3.up);

rotation = Quaternion.AngleAxis(45*Time.deltaTime, Vector3.right) * rotation;



#8 Nypyren   Crossbones+   -  Reputation: 3646

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Posted 30 October 2013 - 01:18 PM

Well, now you're just accumulating everything in the quaternion.



#9 ryt   Members   -  Reputation: 294

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Posted 30 October 2013 - 01:59 PM

Yea, is that good ? The rotation is rotating around Vector3.right in global coord system.






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