Problem with node->SetRotation

Scarabol · Post by **Scarabol** » Sat Apr 18, 2009 11:11 am

Hi,

i have a node, which is rotated to vector3df(360,0,0).

The problem is, when i call setRotation(vector3df(0,0,0), the node rotates 1 time around himself, which looks very ugly and crazy too if the rotations is not 360 but 720 or more...

How can i make vector3df(360,0,0) and vector3df(0,0,0) equal, that the user does not see any difference?

Greetings
Scarabol

arras · Post by **arras** » Sat Apr 18, 2009 12:13 pm

I dont understand your question. 360 and 0 degrees rotations ARE equal. 720 degree rotation does not exist at all. Rotations can exist only between 0-360 degrees.

Scarabol · Post by **Scarabol** » Sat Apr 18, 2009 12:25 pm

Well, i know that they are equal, but Irrlicht doesn't know this...

So if i call node->setRotation(0,0,0);
and then node->setRotation(360,0,0); Irrlicht Rotates the node one the Screen...

Or if the node->getRotation() is (720,0,0) (<< it is possible to make this) and i call node->setRotation(0,0,0) Irrlicht rotates the node twice around his axis

(

Greetings
Scarabol

vipergc · Post by **vipergc** » Sat Apr 18, 2009 12:45 pm

setrotation first converts the degrees to radians by multiplying the angle by DEGTORAD64 and then calculating the sine and cosine in order to apply the rotation...

THEORY:
the trig value of sin(0) = sin(360) = 0
and cos(0) = cos(360) = 1

PRACTICAL:
sin(0) = 0
sin(360) = sin(360 * pi/180) = sin(.0174) = .000303 (not zero)
this is due to floating point limitations on a computing device and the fact that pi is an irrational number. I would suggest that you limit the values to 0-360 from within your code because rotations beyond 360 are essentially wrapped to fit within 0-360 anyway by the trig functions. you cant force the function to do two rotations by passing 720 degrees.

are you hard coding the values you are passing or are they calculated values? if they are calculated, then you may be experiencing errors due to floating point limitations (jitter is a common problem here)
for example sin(360.1) = 0.00174, not zero

Scarabol · Post by **Scarabol** » Sat Apr 18, 2009 12:51 pm

I just use:

Code: Select all

node->setRotation(node->getRotation() + vector3df(-((receiver.mouseY()-device->getVideoDriver()->getScreenSize().Height/2))*0.01f*mainplayer.turnspeed*masterspeed, ((receiver.mouseX()-device->getVideoDriver()->getScreenSize().Width/2))*0.01f*mainplayer.turnspeed*masterspeed, 0)

So it is possible that the node rotates all the time left and in my debug view node->getRotation increase equal to this, also over 360 degree...

Im just looking for a way that the node is just set to the Rotation not rotated to...
So node->setRotation() seems not to do what it should do

Greetings
Scarabol

vipergc · Post by **vipergc** » Sat Apr 18, 2009 1:10 pm

rememeber, setrotation is a RELATIVE rotation and if your calculations are off even by a slight bit, and the function is called numerous times.. it will appear to be showing a slight rotation...

computers are stupid,
they do what we tell them to do,
not what we want them to do

Scarabol · Post by **Scarabol** » Sat Apr 18, 2009 1:57 pm

Is there a function for absolute rotation?

The problem is that the node is rotated and not set to the rotation...

Greetings
Scarabol

vipergc · Post by **vipergc** » Sun Apr 19, 2009 12:41 am

Are you looking for something that will actually animate the rotation?
The setrotation() function will simply perform rotation in the 3D sense, that is the object will be rotated into a particular position..
if you are looking to spin an object, then you can either use an animated mesh object or program the rotation angle as a varying quantity and then call the setrotation() within that loop

Scarabol · Post by **Scarabol** » Sun Apr 19, 2009 12:52 am

I think this shows what i mean:

Code: Select all

while (device->run())
{
node->setrotation(vector3df(180,0,0)-node->getrotation());
}

Well first, i know there is some code missing, but not necessary

I think the node should only have 2 states on screen, one with xangle = 0 and one with xangle = 180, but as u can see the node has some interstates which make him flip around, like a gyroscope...

Greetings
Scarabol

arras · Post by **arras** » Sun Apr 19, 2009 7:47 am

I think either we misunderstand your question or you misunderstand rotations in Irrlicht.

If you call setRotation on node, it will change nodes rotation relative to its parent node. If node does not have parent, than relative to global space which means it will be absolute rotation.

If you want to rotate node relative to its own rotation, not rotation of its parent, than you have to use different approach.

If you execute code:

Code: Select all

while (device->run())
{
node->setrotation(vector3df(180,0,0)-node->getrotation());
}

and your node flips like a gyroscope, then thats perfectly fine. You ordered it to do so:

Say original rotation is 0
1th loop: 180 - 0 = 180
2nd loop: 180 - 180 = 0
3rd loop: 180 - 0 = 180
4th loop: 180 - 180 = 0

As you see you turn your node 180 degrees each frame.

Scarabol · Post by **Scarabol** » Sun Apr 19, 2009 10:36 pm

I'm have to say sorry to everyone, who helped me in this case, it was my mistake, i'm sorry

[CLOSED]

Greetings
Scarabol

vipergc · Post by **vipergc** » Mon Apr 20, 2009 12:05 am

Not a problem... kudos to you... there are those.. who will never admit having screwed up...