Develop Reference

Unity 3D - How to gllobaly rotate one object based on second

I have got a very large problem with rotation in Unity. What I want:
I have two 3D objects. Just one is for player manipulating, second object Transform.rotation and Transform.position is dependent on object number one with scale of 1/10. It means if I will move first object from (0,0,0) to (10,30,90) then obj.2 will move from (0,0,0) to (1,3,9). It's simple. But I have got LARGE problem with rotation.
I can't make rotation on normal transform because it's based on "local position".
Below I present my problem with simplest 2D object situation:
As you can see when I rotate red object +90 degrees the second object rotate +9 degrees and the axes become different in relation to the world. After more transformations in 3D world it make a large mess. For example after some transformations if I will want to rotate 3D object from me (like using accelerator on motocycle) on first make second object rotating from left to right (because it's based on object axis).
Of course using Transform.Rotate instead of Transform.localRotate (or Transform.EulerAngles instead of Transform.localEulerAngles) is not a solutions because it's means only if objects are childrens (it this this case are not).
WHAT I FOUND:
Using Transform.Rotate(Xdegree,Ydegree,Zdegree, Space.World) is solution for rotating second object !
What I need:
Xdegree, Ydegree and Zdegree from first (manipulated by player) object.
Transform.EulerAngles and Transform.Rotation DOESN'T work because it's returns "local objects" rotations.
So... I know that if 3D obj.2 rotation is (0;30;0) and i use obj2.Rotate(45,0,0) then the obj.2 rotation will be (~37.76;~39.23;~26.56) and it's okay. But I dont know how to convert the other way (from "local" rotation XYZ to degrees that I can use on Transform.Rotate() (of course I will divided this values (xyz) by 10 at the end because I have got 1/10 moving scale))

If you need one GameObject to have 1/10 of the rotation and position of another, you could use something like:
//the player-controlled cube
public Transform t1;
//the 1/10 cube
public Transform t2;
void Update(){
//set the position of t2 to 1/10 of the position of t1
t2.position = 0.1f * t1.position;
//get the axis and angle of t1's rotation
t1.rotation.ToAngleAxis(out float angle, out Vector3 axis);
//t2 should be rotated in the same direction (axis), but with 1/10th of the angle
t2.rotation = Quaternion.AngleAxis(angle * 0.1f, axis);
}
Edit: To allow resetting delta rotation and changing targets, you could do something like this. Note: this glitches when it wraps more than a full circle, I'm not an expert on Quaternions so you'd have to figure it out yourself.
//the player-controlled cube
public Transform t1;
//the 1/10 cube
public Transform t2;
private Vector3 t1originalPosition;
private Quaternion t1originalRotation;
private Vector3 t2originalPosition;
private Quaternion t2originalRotation;
void Start()
{
ResetTarget(t1);
}
void Update()
{
if (t1 != null)
{
//set the position of t2 to 1/10 of the position of t1
t2.position = t2originalPosition + 0.1f * (t1.position - t1originalPosition);
Quaternion t1Rotation = t1.rotation * Quaternion.Inverse(t1originalRotation);
//get the axis and angle of t1's rotation
t1Rotation.ToAngleAxis(out float angle, out Vector3 axis);
//t2 should be rotated in the same direction (axis), but with 1/10th of the angle
t2.rotation = Quaternion.AngleAxis(angle * 0.1f, axis) * t2originalRotation;
}
}
public void ResetTarget(Transform target = null)
{
t2originalPosition = t2.position;
t2originalRotation = t2.rotation;
t1 = target;
t1originalPosition = t1.position;
t1originalRotation = t1.rotation;
}

Use quaternions instead of the euler angles (xyz rotation angles). And simply give the global rotation value (quaternion) of one object to the other.
To add together quaternions, you just multiply them together.

Stabilize object on one axis only

i am trying to stabilize my object to not fall aside. This code works pretty good, but it also stabilize the object to not fall forward or backward.
Is there any possibility to restrict this to only one axis?
var deltaQuat = Quaternion.FromToRotation(_rBody.transform.up, Vector3.up);
deltaQuat.ToAngleAxis(out var angle, out var axis);
_rBody.AddTorque(-_rBody.angularVelocity * 2f, ForceMode.Acceleration);
_rBody.AddTorque(axis.normalized * angle * 5f, ForceMode.Acceleration);

Use the contrints in the rigidbody component:

As I understand your goal is to constraint the rotation on a certain local axis.
You could probably do it somewhat similar to this post just not for positions but rotations going through Rigidbody.angularVelocity.
// get the angularVelocity but in local space relative to the current rigidbody orientation
var localAngularVelocity = Quaternion.Inverse(rigidbody.rotation) * rigidbody.angularVelocity;
// get the euler space representation
var localAngularEulers = localAngularVelocity.eulerAngles;
// now constraint according to your needs e.g. on the local forward axis
localEulerAngles.z = 0;
// now convert back and assign
rigidbody.angularVelocity = rigidbody.rotation * Quaternion.Euler(localAngularEulers);
Note: Typing on smartphone so can't test it right now but I hope the idea gets clear

Diagonal speed is too fast

How can I keep the diagonal speed to be the same as the horizontal and vertical speed without clamping any value or using ".normaized". I tryed to normalize the values but I lost the joystick values between 1 and 0. Here is my code :
void ListenInput()
{
Vector3 rightDirection = camera.right;
Vector3 frontDirection = camera.GetForwardFromAngleY();
move = new Vector2(
Input.GetAxis("Horizontal"),
Input.GetAxis("Vertical")
);
MoveCharacter(rightDirection * move.x);
MoveCharacter(frontDirection * move.y);
}
void MoveCharacter(Vector3 velocity)
{
transform.position += velocity * Time.deltaTime * runningSpeed;
}

Here, you should clamp the magnitude of the input Vector2.
For example with Vector2.ClampMagnitude() from the Unity API.
That will keep the input non-binary and prevent the diagonal from getting larger than purely horizontal/vertical inputs.
void ListenInput()
{
Vector3 rightDirection = camera.right;
Vector3 frontDirection = camera.GetForwardFromAngleY();
move = new Vector2(
Input.GetAxis("Horizontal"),
Input.GetAxis("Vertical")
);
move = Vector2.ClampMagnitude(move, 1f);
MoveCharacter(rightDirection * move.x);
MoveCharacter(frontDirection * move.y);
}
void MoveCharacter(Vector3 velocity)
{
transform.position += velocity * Time.deltaTime * runningSpeed;
}

If you normalize a vector you will make sure it's length is 1. This is a great way to avoid quirks like "diagonal movement is faster than normal movement".
However, the fact that the length is always 1 also means that there is no "move slowly" or "move at full speed" distinction from the joystick. When you say "I lost the joystick values between 1 and 0" is due to this fact.
One way developers get around this is by using a mathematical formula to scale the speed.
You could:
Use the largest value (horizontal or vertical) to control the speed
Use the smallest value
Use a combination of the two
Another way to do this is to store how long ago the movement started, then scale the speed based on that. This method has its own challenges, but is very familiar to players.
Examples
For instance, if I have:
horizontalInput = 1
verticalInput = 0.5
This means my normalized vector looks like this:
I could:
Use the largest value
Move at full speed (1) on the direction of my vector.
Use the smallest value
Move at half speed (0.5) on the direction of my vector.
Use a Use a combination of the two values
For this instance, lets use the following formula: (x+y)/2.
Move at 3/4 speed (0.75) on the direction of my vector.
NOTE: This formula will not "feel" as nice if you have x=0 and y=1, this is just an example. You most likely want to use Min, Max, Avg and if-clauses to control how the speed works.
You can use different formulas and different techniques to make the movement in your game feel like what you want, but take the time to analyze WHY it feels like that.

Physics Simulation Ensuring Circles Do Not Overlap - C# XNA 4.0

Okay, so I am trying to simulate the collision of balls on a 2-Dimensional plane. I can detect the collisions pretty easily using a simple comparison of positions and the sum of radii, however, sometimes the simulation gets ahead of itself and the circles overlap, which plays havoc with the rest of the simulation.
So I have figured that finding the normal vector between the two circles at the point of contact and adding onto the position vectors in that direction is what I need to do basically, and luckily I had a similar algorithm handling the velocity changes due to collisions so I adapted it thusly:
Vector2 normal = orgA.getCenterPosition() - orgB.getCenterPosition();
Vector2 tangent = new Vector2((normal.Y * -1), normal.X);
float diff = (orgA.getRadius() + orgB.getRadius()) - normal.Length();
normal.Normalize();
float PAn = Vector2.Dot(normal, orgA.position);
float PAt = Vector2.Dot(tangent, orgA.position);
PAn += diff;
float PBn = Vector2.Dot(normal, orgB.position);
float PBt = Vector2.Dot(tangent, orgB.position);
PBn -= diff;
Vector2 PA = (PAn * normal) + (PAt * tangent);
Vector2 PB = (PBn * normal) + (PBt * tangent);
orgA.position = PA;
orgB.position = PB;
The trouble is that when I run the simulation, and two balls meet, the whole thing goes crazy and they're suddenly going all over the shop.
Can anyone see the flaw in my algorithm? I've looked at it loads and I still can't find what's causing this.

Hey buddy i think what you need is a loop. Its going crazy because once the balls touch they are constantly being upgraded with a new logic....
im not amazing at this but try putting the collision in a loop... should look something like this:
if ( diff < (orb radius))
{
Vector2 PA = (PAn * normal) + (PAt * tangent);
Vector2 PB = (PBn * normal) + (PBt * tangent);
orgA.position = PA;
orgB.position = PB;
}
something like that... I really hope this helps a little :/
from my understanding is this is in your update method, so keep in mind update runs constantly every millisecond... so its fine when your getting the difference between the spheres and sizes but after they collide and you you want them to move in a certain way you are calculating the same equation over and over...
Better yet make a bool such as isCollided and make sure you switch that true/false according to that statement
hope it helps i have an example project of collision if you want i can send it to you, samerhachem#hotmail.com

Distance between Matrix Objects, relative to parents orientation, using XNA?

I would like to understand how to measure the distance between two 3D objects, let's call them a parent object and a child object. Think of the parent as the body of a car and the child being a wheel of the car.
I understand how to get the difference based on the objects position in world space but I would like to get the difference as a measurement based on the parents relative object space. 
E.g if the parent is facing East and the child is 2X, 3Y from the parent, measured in a relative sense. Such that if the parent rotated 60 degrees, the relative location of the child remains at a distance of 2x, 3y in the object space. Where as in a world space sense the child objects measurement as a Vector3 would be quite different. 
Basically I just want a predictable way to get the difference so that a child object which is on the right of the patent can always stay right of the parent object. 
This is the parent component, this update is run every frame:
[Serializable]
public class Component_Parent : BaseComponentAutoSerialization<ISceneEntity>
{
public override void OnUpdate(GameTime gameTime)
{
PassThrough.ParentMatrix = ParentObject.World;
PassThrough.ParentTranslation = ParentObject.World.Translation;
}
}
This next part is the child component:
[Serializable]
public class Component_Child : BaseComponentAutoSerialization<ISceneEntity>
{
Vector3 _parentOffset;
Quaternion _parentQuaternionOffset;
public override void OnUpdate(GameTime gameTime)
{
// Get a sceneobject from the ParentObject
SceneObject sceneobject = (SceneObject)ParentObject;
// This relies on the position never being at 0,0,0 for setup, so please don't do that
// or change it with more look ups so that you don't need to rely on a Zero Vector3 :-)
if (PassThrough.GroupSetupMode || _parentOffset == Vector3.Zero)
{
if (PassThrough.ParentTranslation != Vector3.Zero)
{
_parentOffset = sceneobject.World.Translation - PassThrough.ParentTranslation;
// Decompose World Matrix (Parent)
Quaternion parentQ = new Quaternion();
Vector3 parentSpot = new Vector3();
Vector3 parentScale = new Vector3();
PassThrough.ParentMatrix.Decompose(out parentScale, out parentQ, out parentSpot);
Matrix identity = Matrix.Identity;
// Decompose Identity Matrix (Parent)
Quaternion identityQ = new Quaternion();
Vector3 identitySpot = new Vector3();
Vector3 identityScale = new Vector3();
identity.Decompose(out identityScale, out identityQ, out identitySpot);
_parentQuaternionOffset = identityQ - parentQ;
}
}
else
{
if (_parentOffset != Vector3.Zero)
{
// Decompose World Matrix (Child)
Quaternion rotationQ = new Quaternion();
Vector3 spot = new Vector3();
Vector3 scale = new Vector3();
sceneobject.World.Decompose(out scale, out rotationQ, out spot);
// Decompose World Matrix (Parent)
Quaternion parentQ = new Quaternion();
Vector3 parentSpot = new Vector3();
Vector3 parentScale = new Vector3();
PassThrough.ParentMatrix.Decompose(out parentScale, out parentQ, out parentSpot);
Matrix location = Matrix.CreateTranslation(PassThrough.ParentTranslation);
Matrix rotation = Matrix.CreateFromQuaternion(parentQ);
Matrix rotation2 = Matrix.CreateFromQuaternion(_parentQuaternionOffset);
Matrix newWorld = rotation * location;
Vector3 testTranslation = newWorld.Translation + ((newWorld.Left * _parentOffset.X) + (newWorld.Up * _parentOffset.Y) + (newWorld.Forward * _parentOffset.Z));
Matrix scaleM = Matrix.CreateScale(scale);
//sceneobject.World = scaleM * (rotation * (Matrix.CreateTranslation(testTranslation)));
sceneobject.World = (Matrix.CreateTranslation(testTranslation));
}
}
}
}
I think it has something to do with keeping track of an offset rotation, from the identity matrix and I have started trying to add some code to that effect but really unsure of what next now.
Additional:
If I have the parent object facing the direction of the world space it all works, if it's facing a different direction then it's an issue and the child seems to rotate by the same amount when they are grouped together.
I've uploaded a demo video to try and explain:
http://www.youtube.com/watch?v=BzAKW4WBWYs
I've also pasted up the complete code for the components, the static pass through and the scene entity.
http://pastebin.com/5hEmiVx9
Thanks

Think wheels on a car. I want the right wheel to always be in the same
spot relative to the body of the car.
It sounds like you want to be able to locate the position of the wheel for any given orientation or position of the car. One built in method that XNA has to help here is Model.CopyAbsoluteBoneTransformsTo(Matrix[]); However, your code looks like you want to handle parent child relationship manually. So here is a way to do it without using the built in method. It assumes you do have offset information at load time:
Before the game loops starts (say, in the LoadContent method), after loading the car & wheel and assuming they load into the proper positions, you can then create your offset vector ( _parentOffset )
Vector3 _parentOffset = wheel.meshes[?].ParentBone.Transform.Translation - car.meshes[?].ParentBone.Transform.Translation;//where ? is the mesh index of the mesh you are setting up.
Save that vector and don't modify it.
Later, after the car's matrix has been rotationally and or positionally displaced, set the wheel's matrix like this:
Matrix wheelMatrix = carMatrix;
wheelMatrix.Translation += (wheelMatrix.Right * _parentOffset.X) +
(wheelMatrix.Up * _parentOffset.Y) +
(wheelMatrix.Backward * _parentOffset.Z);
This allows that the wheel matrix will inherit any rotational and translational information from the car but will displace the wheel's position appropriately regardless of car's orientation/position.

The distance between two objects is NOT a function of either orientations.
What you basically want is the distance of the child object to the orientation line of the parent object. Assuming you have a global cartesian coordinate system this can be simply calculated as h=sqrt(x^2+y^2)*sin(Theta), x and y being the relative coordinates of the child with respect to the parent and Theta the orientation of the parent measured from x axis.
But still the question is a little bit confusing to me. If you only want to make sure that the child is on the right side of the parent why don't you simply check the relative x? If it's positive it's on the right and if it's negative it's on the left?

The issue was the way I was trying to use the offset of the world space.
Thanks to flashed from #XNA on EFnet, this code works perfectly:
[Serializable]
public class Component_Child_fromxna : BaseComponentAutoSerialization<ISceneEntity>
{
Vector3 _parentOffset;
Matrix _ParentMatrixOffset;
public override void OnUpdate(GameTime gameTime)
{
// Get a sceneobject from the ParentObject
SceneObject sceneObject = (SceneObject)ParentObject;
// This relies on the position never being at 0,0,0 for setup, so please don't do that
// or change it with more look ups so that you don't need to rely on a Zero Vector3 :-)
if (PassThrough.GroupSetupMode || _parentOffset == Vector3.Zero)
{
if (PassThrough.ParentTranslation != Vector3.Zero)
{
// The old offset - This is just in world space though...
_parentOffset = sceneObject.World.Translation - PassThrough.ParentTranslation;
// Get the distance between the child and the parent which we keep as the offset
// Inversing the ParentMatrix and multiplying it by the childs matrix gives an offset
// The offset is stored as a relative xyz, based on the parents object space
_ParentMatrixOffset = sceneObject.World * Matrix.Invert(PassThrough.ParentMatrix);
}
}
else
{
if (_parentOffset != Vector3.Zero)
{
//Matrix pLocation = Matrix.CreateTranslation(_parentOffset);
//sceneObject.World = Matrix.Multiply(pLocation, PassThrough.ParentMatrix);
sceneObject.World = Matrix.Multiply(_ParentMatrixOffset, PassThrough.ParentMatrix);
}
}
}
}