mojo3d: Entity in view?

[Cole ChapmanParticipant]

Trying to implement it myself — I have added the class in the bullet module.  I decided to make a new “constraint” class for mojo3d but when I call on the bullet command btPoint2PointConstraint, I get:

bullet3-2.85.1/src/BulletDynamics/ConstraintSolver/btPoint2PointConstraint.h:77:2: note: no known conversion for argument 1 from ‘btRigidBody*’ to ‘btRigidBody&’

It passes the btRigidBody(s) and btVector3(s) but appears Var is still not implemented so I am unsure how to pass references instead of pointers.

Any ideas?

[Mark SiblyKeymaster]

Can you post the stuff you’ve added to bullet.monkey2 (or all of it)?

[Cole ChapmanParticipant]

It’s not anything so far —

Bullet:

Monkey

Class btTypedObject Extends btObject End Class btTypedConstraint Extends btTypedObject End Class btPoint2PointConstraint Extends btTypedConstraint Method New( rbA:btRigidBody, rbB:btRigidBody, pivotInA:btVector3, pivotInB:btVector3 ) Method New( rbA:btRigidBody, pivotInA:btVector3 ) End

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Class btTypedObject Extends btObject End   Class btTypedConstraint Extends btTypedObject End   Class btPoint2PointConstraint Extends btTypedConstraint Method New( rbA:btRigidBody, rbB:btRigidBody, pivotInA:btVector3, pivotInB:btVector3 ) Method New( rbA:btRigidBody, pivotInA:btVector3 ) End

 

mojo3d/scene/components/constraint:

Monkey

Namespace mojo3d Private Class Constraint Extends Component End Class Point2PointConstraint Extends Constraint Method New( rigid1:btRigidBody, rigid2:btRigidBody, pos1:Vec3f, pos2:Vec3f) Local btVec1:=New btVector3(pos1.x, pos1.y, pos1.z) Local btVec2:=New btVector3(pos2.x, pos2.y, pos2.z) _btConstraint = New btPoint2PointConstraint(rigid1, rigid2, btVec1, btVec2) End Field _btConstraint:btPoint2PointConstraint End

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Namespace mojo3d   Private   Class Constraint Extends Component End   Class Point2PointConstraint Extends Constraint   Method New( rigid1:btRigidBody, rigid2:btRigidBody, pos1:Vec3f, pos2:Vec3f) Local btVec1:=New btVector3(pos1.x, pos1.y, pos1.z) Local btVec2:=New btVector3(pos2.x, pos2.y, pos2.z)   _btConstraint = New btPoint2PointConstraint(rigid1, rigid2, btVec1, btVec2) End Field _btConstraint:btPoint2PointConstraint End

[Mark SiblyKeymaster]

Hmm, that’s weird, bullet is using references instead of pointers here.

The easiest way to deal with this right now is probably to just add pointer versions of the ctors, eg:

btPoint2PointConstraint(btRigidBody* rbA,btRigidBody* rbB, const btVector3& pivotInA,const btVector3& pivotInB):
btPoint2PointConstraint(*rbA,*rbB,pivotInA,pivotInB){}

btPoint2PointConstraint(btRigidBody* rbA,const btVector3& pivotInA):
btPoint2PointConstraint(*rbA,pivotInA){}

Add this directly to the btPoint2PointConstraint.h file below the existing ctors – I haven’t tested it but it compiles at least. The nicer way is probably to subclass btPoint2PointConstraint and add the new ctors there, but this should get you going for now.

No idea why he’s done it this way, the joys of c++!

[Mark SiblyKeymaster]

Actually, I’m up for having a go at getting a point2point constraint style component (or whatever) going right now, got nothing else on.

[Cole ChapmanParticipant]

Aww Yiss!

[Mark SiblyKeymaster]

I know little to nothing about constraints though! Should I just start with the simple 1 body, 1 pivot point2point type? How does/should this work? What would be a good little demo for this?

[Cole ChapmanParticipant]

Maybe DruggedBunny can add some input but this is what I have been looking at:

btPoint2PointConstraint Class Reference

Bullet’s Wiki – Constraints

Convoluted Demo

Snippet of Panda3D’s Implementation

Bullet – Chain Tutorial (Using Point2Point/Ball Socket Constraints)

You could start with either but I feel like the 2 body-2pivot point2point will help you see if it’s actually working or not – not really sure when someone would use 1 body-1 pivot.

I was thinking of the actual user-facing code looking something like:

Monkey

Function Setup() Local Cone1:=Model.CreateCone( 2.5, 5, Axis.Y, 32, New PbrMaterial( Color.Red ), Null ) Cone1.Move( 0, 20, 0 ) Local Cone1Rigid:=New RigidBody( Cone1 ) Local Cone1Tip:= New Vec3f '(Position of tip of cone) Local Cone2:=Model.CreateCone( 2.5, 5, Axis.Y, 32, New PbrMaterial( Color.Green ), Null ) Cone2.Move( 0, 20, 0 ) Cone2.Rotate( 0, 0, 180 ) Local Cone2Rigid:=New RigidBody( Cone2 ) Local Cone2Tip:= New Vec3f '(Position of tip of cone) 'Local Link:Constraint = New Point2PointConstraint(Cone1Rigid, Cone2Rigid, Cone1Tip, Cone2Tip) ...Or Local Link:Constraint = New BallSocketConstraint(Cone1Rigid, Cone2Rigid, Cone1Tip, Cone2Tip) #rem Possible Commands: Constraint.SetPivot(someVec3, Null) 'set PivotA and keep/ignore PivotB Constraint.GetPivot(pivA, pivB) 'return pivots/vectors Constraint.SetLimits() 'not 100% on how limits would work #end End

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Function Setup() Local Cone1:=Model.CreateCone( 2.5, 5, Axis.Y, 32, New PbrMaterial( Color.Red ), Null ) Cone1.Move( 0, 20, 0 ) Local Cone1Rigid:=New RigidBody( Cone1 ) Local Cone1Tip:= New Vec3f '(Position of tip of cone) Local Cone2:=Model.CreateCone( 2.5, 5, Axis.Y, 32, New PbrMaterial( Color.Green ), Null ) Cone2.Move( 0, 20, 0 ) Cone2.Rotate( 0, 0, 180 ) Local Cone2Rigid:=New RigidBody( Cone2 ) Local Cone2Tip:= New Vec3f '(Position of tip of cone) 'Local Link:Constraint = New Point2PointConstraint(Cone1Rigid, Cone2Rigid, Cone1Tip, Cone2Tip) ...Or Local Link:Constraint = New BallSocketConstraint(Cone1Rigid, Cone2Rigid, Cone1Tip, Cone2Tip) #rem Possible Commands: Constraint.SetPivot(someVec3, Null) 'set PivotA and keep/ignore PivotB Constraint.GetPivot(pivA, pivB) 'return pivots/vectors Constraint.SetLimits() 'not 100% on how limits would work #end End

Going to be honest I have never really dealt with constraints and if you need me to find some more examples/references I absolutely will.  Having said all that, Point2Point looks like it really dives right into it and I think once you get this, other constraints like Hinge etc. should be a bit easier – if you’re up for the challenge!

Edit: Couple more links:

Bullet Manual – Page 23 (Constraints)

Bullet – Bridge Tutorial (Uses Point2Point Constraints)

[Mark SiblyKeymaster]

Attempt #1 is now up at develop!

There’s a simple test in the tests dir called ‘constraints.monkey2’. It’s just a basic chain of cubes, but it seems to work OK.

One weird thing is the chain should be ‘anchored’ by the cube at the top, and it sort of is, however the bottom cubes shouldn’t touch the ground but they do a little, not sure what’s up there yet…

[Cole ChapmanParticipant]

This is great!  Thank you so much Mark!

[DruggedBunnyParticipant]

Cool, works here. It looks correct — guessing the constraints have a little ‘flex’ in them at first glance, rather than being set to a fixed distance? Will dig in…

EDIT: Hmm, see what you mean…

[DruggedBunnyParticipant]

Little bit of debugging output in attached image… not sure what it means yet!

Once settled, there’s (as expected) ~1.2 distance between each box, with 10 boxes, but their y-position isn’t at the original y-position, so I think the constraints must have a default ‘looseness’ to them. Tried the bullet docs, but they’re impenetrable and don’t actually detail what the constraint settings are for (ERP??).

Attachments:

1. 

   constraints.jpg
   

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