How to rotate a 3d physics object to a target rotation?

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Mambazo

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Posted: 17th May 2020 11:33

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Hello!

Having fun with AGKVR.

Moving a physics object gradually to a desired position is working perfectly. (Like a Jedi using the force

)

+ Code Snippet


// target position

opos_x# = GetObjectX( my_object )
opos_y# = GetObjectY( my_object )
opos_z# = GetObjectZ( my_object )

tpos_x# = AGKVR.GetLeftHandX()
tpos_y# = AGKVR.GetLeftHandY()
tpos_z# = AGKVR.GetLeftHandZ()	
		
x_diff# = tpos_x# - opos_x#
y_diff# = tpos_y# - opos_y#
z_diff# = tpos_z# - opos_z#
				
direction = CreateVector3( x_diff#, y_diff#, z_diff# )
		
object_pos = CreateVector3( opos_x#, opos_y#, opos_z#  )
target_pos = CreateVector3( tpos_x#, tpos_y#, tpos_z# )
		
SetObject3DPhysicsLinearVelocity( my_object, direction, GetVector3Distance( object_pos, target_pos ) * 10 )

However I'm having trouble rotating the physics object to a desired angle.

I seem to encounter gimbal lock issues and the object rotation begins to twitch erratically.

Any ideas on how to do it?

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blink0k

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Posted: 17th May 2020 21:27

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Have a look at SetObject3DPhysicsAngularVelocity()

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Mambazo

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Posted: 17th May 2020 21:50

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I was using SetObject3DPhysicsAngularVelocity() and seeing erratic rotation behaviour. I am obviously doing it wrong but I'm having trouble finding any information about how to do it right.

In the VR example projects, they are using contact and joints, which is fine if you don't want the object to snap to a specific rotation when it reaches your hand (such as a ball) but that doesn't suit something like a sword.

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blink0k

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Posted: 18th May 2020 21:40

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Do you have some sample code?

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Mambazo

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Posted: 18th May 2020 22:20 Edited at: 18th May 2020 23:54

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This is what I have so far. It seems to work in limited ranges, but goes bananas at certain angles.

This function is supposed to apply angular force to an object so that it will eventually reach the same orientation as the target_obj

Thanks

function rotate_toward_physics( obj, target_obj )
	
	trot_x# = GetObjectWorldAngleX( target_obj )
	trot_y# = GetObjectWorldAngleY( target_obj )
	trot_z# = GetObjectWorldAngleZ( target_obj )
	
	if trot_x# < 0 then trot_x# = trot_x# + 360
	if trot_y# < 0 then trot_y# = trot_y# + 360
	if trot_z# < 0 then trot_z# = trot_z# + 360

if trot_x# >  360 then trot_x# = trot_x# - 360
	if trot_y# >  360 then trot_y# = trot_y# - 360
	if trot_z# >  360 then trot_z# = trot_z# - 360
	
	crot_x# = GetObjectWorldAngleX( obj )
	crot_y# = GetObjectWorldAngleY( obj )
	crot_z# = GetObjectWorldAngleZ( obj )
	
	if crot_x# < 0 then crot_x# = crot_x# + 360
	if crot_y# < 0 then crot_y# = crot_y# + 360
	if crot_z# < 0 then crot_z# = crot_z# + 360
	
	if crot_x# > 360 then crot_x# = crot_x# - 360
	if crot_y# >  360 then crot_y# = crot_y# - 360
	if crot_z# >  360 then crot_z# = crot_z# - 360		
	
	x_rot# = trot_x# - crot_x#
	y_rot# = trot_y# - crot_y#
	z_rot# = trot_z# - crot_z#

if x_rot# < 0 then x_rot# = x_rot# + 360
	if y_rot# < 0 then y_rot# = y_rot# + 360
	if z_rot# < 0 then z_rot# = z_rot# + 360

if x_rot# > 360 then crot_x# = crot_x# - 360
	if y_rot# >  360 then crot_y# = crot_y# - 360
	if z_rot# >  360 then crot_z# = crot_z# - 360

if x_rot# >= 180 then x_rot# = -(360 - x_rot#)
	if y_rot# >= 180 then y_rot# = -(360 - y_rot#)
	if z_rot# >= 180 then z_rot# = -(360 - z_rot#)

if x_rot# <= -180 then x_rot# = (360 + x_rot#)
	if y_rot# <= -180 then y_rot# = (360 + y_rot#)
	if z_rot# <= -180 then z_rot# = (360 + z_rot#)
			
	direction = CreateVector3( x_rot#, y_rot#, z_rot# )
	cube_rot = CreateVector3( crot_x#, crot_y#, crot_z# )
	target_rot = CreateVector3( trot_x#, trot_y#, trot_z# )

SetObject3DPhysicsAngularVelocity( obj, direction, GetVector3Length( direction ) * 0.5 )
endfunction

+ Code Snippet

function rotate_toward_physics( obj, target_obj )
	
	trot_x# = GetObjectWorldAngleX( target_obj )
	trot_y# = GetObjectWorldAngleY( target_obj )
	trot_z# = GetObjectWorldAngleZ( target_obj )
	
	if trot_x# < 0 then trot_x# = trot_x# + 360
	if trot_y# < 0 then trot_y# = trot_y# + 360
	if trot_z# < 0 then trot_z# = trot_z# + 360

	if trot_x# >  360 then trot_x# = trot_x# - 360
	if trot_y# >  360 then trot_y# = trot_y# - 360
	if trot_z# >  360 then trot_z# = trot_z# - 360
	
	crot_x# = GetObjectWorldAngleX( obj )
	crot_y# = GetObjectWorldAngleY( obj )
	crot_z# = GetObjectWorldAngleZ( obj )
	
	if crot_x# < 0 then crot_x# = crot_x# + 360
	if crot_y# < 0 then crot_y# = crot_y# + 360
	if crot_z# < 0 then crot_z# = crot_z# + 360
	
	if crot_x# > 360 then crot_x# = crot_x# - 360
	if crot_y# >  360 then crot_y# = crot_y# - 360
	if crot_z# >  360 then crot_z# = crot_z# - 360		
	
	x_rot# = trot_x# - crot_x#
	y_rot# = trot_y# - crot_y#
	z_rot# = trot_z# - crot_z#

	if x_rot# < 0 then x_rot# = x_rot# + 360
	if y_rot# < 0 then y_rot# = y_rot# + 360
	if z_rot# < 0 then z_rot# = z_rot# + 360

	if x_rot# > 360 then crot_x# = crot_x# - 360
	if y_rot# >  360 then crot_y# = crot_y# - 360
	if z_rot# >  360 then crot_z# = crot_z# - 360		

	if x_rot# >= 180 then x_rot# = -(360 - x_rot#)
	if y_rot# >= 180 then y_rot# = -(360 - y_rot#)
	if z_rot# >= 180 then z_rot# = -(360 - z_rot#)

	if x_rot# <= -180 then x_rot# = (360 + x_rot#)
	if y_rot# <= -180 then y_rot# = (360 + y_rot#)
	if z_rot# <= -180 then z_rot# = (360 + z_rot#)
			
	direction = CreateVector3( x_rot#, y_rot#, z_rot# )
	cube_rot = CreateVector3( crot_x#, crot_y#, crot_z# )
	target_rot = CreateVector3( trot_x#, trot_y#, trot_z# )

	SetObject3DPhysicsAngularVelocity( obj, direction, GetVector3Length( direction ) * 0.5 )
endfunction

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blink0k

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Posted: 19th May 2020 00:22

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Try SetObject3DPhysicsCanSleep(obj, 0)
You will need to check the rotation values are close enough in order to stop the rotation when they match

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Mambazo

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Posted: 19th May 2020 00:36 Edited at: 19th May 2020 00:37

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Thanks, but perhaps this video will illustrate better the issue I'm having

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blink0k

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Posted: 19th May 2020 01:15

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So this is a different problem then?

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Mambazo

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Posted: 19th May 2020 10:06

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The desired result is that the object (rubiks cube) matches the orientation of the hand (the yellow box).

The problem is that it doesn't always match the orientation of the hand.

So I am obviously doing something wrong and would like some help figuring it out.

¯\_(ツ)_/¯

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Anthony Brian Cox

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Posted: 19th May 2020 18:30

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have you tryed usin a vector 3 from the hand angle (vector3=createvector3(getobjecanglex(ob),(getobjecangley(ob)(getobjecanglez(ob))

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Mambazo

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Posted: 19th May 2020 18:35

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Thanks for taking a look.

Quote: "have you tryed usin a vector 3 from the hand angle (vector3=createvector3(getobjecanglex(ob),(getobjecangley(ob)(getobjecanglez(ob))"

I don't quite understand. Can you elaborate on what you would do with the vector in relation to the code snippet above?

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Mambazo

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Posted: 19th May 2020 23:07 Edited at: 19th May 2020 23:08

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Here is a test using Create3DPhysicsFixedJoint() to attach the cube to the hand object.

The hand object is a KinematicBody positioned at the RightController by SetObjectPosition and SetObjectRotation.

I've added the X, Y and Z axis (Red, Green, Blue respectively) so you can see the orientation of the hand.

This appears to be exhibiting the same orientation behaviour as seen in the previous video.

Am I doing something wrong or is there a bug?

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blink0k

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Posted: 19th May 2020 23:31

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I think you will have a problem when you are crossing axis. Like going from 5 to -160 for example.
If the cube is ALWAYS going to match the rotation of the hand object. Maybe make the cube NOT a physics object and simply match the rotations of the Hand.
If you want to do something else, like throw the cube, then you could create a physics body then and apply the appropriate forces.

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Mambazo

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Posted: 20th May 2020 00:20

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Quote: "I think you will have a problem when you are crossing axis. Like going from 5 to -160 for example."

I notice the 6DOFJoint doesn't have this issue. It can swing in all directions quite happily.

Quote: "If the cube is ALWAYS going to match the rotation of the hand object. Maybe make the cube NOT a physics object and simply match the rotations of the Hand.
If you want to do something else, like throw the cube, then you could create a physics body then and apply the appropriate forces."

Yes this is something I tried, and it works, but I wasn't sure if there was a better way. I had tried it so that when you grab a cube it would turn into a Kinematic body, so that I could use SetObjectRotation and still have the held cube affect other physics objects, which works perfectly up until you want to throw it, like you said.

I will implement it this way again and apply forces when the grip is released.

Thanks for the help

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