Drag box2d at fixture at position clicked without bouncy point

Pkeod · November 3, 2020, 5:46am

I’m trying to mimic something like this

Here’s my wip. I’m not sure how phaser does it. I tried making the joint 0 length but it’s still bouncy around the joint point which I don’t want. The phaser example does a good job o finding the point and sticking to it, no matter what I do with Defold it’s always bouncy and never finds the point easily (or is not strong enough to follow the mouse / even then it feels weird).

Any ideas on how to improve this?

Videos below showing current behavior / closer to what I want

Pkeod · November 3, 2020, 6:17am

I think I want a Mouse Joint?

defold/engine/physics/src/box2d/Box2D/Dynamics/Joints at 869a87718757bdb7bfd6ed078047fa7bfb451de9 · defold/defold · GitHub

So it would need to be added here and a few other places with the right settings…

github.com/defold/defold

engine/physics/src/physics/physics_2d.cpp

a0c1b01f6


      
              return true;
          }
          
          bool GetJointParams2D(HWorld2D world, HJoint _joint, dmPhysics::JointType type, ConnectJointParams& params)
          {
              float inv_scale = world->m_Context->m_InvScale;
          
              b2Joint* joint = (b2Joint*)_joint;
              params.m_CollideConnected = joint->GetCollideConnected();
          
              switch (type)
              {
                  case dmPhysics::JOINT_TYPE_SPRING:
                      {
                          b2DistanceJoint* typed_joint = (b2DistanceJoint*)joint;
                          params.m_SpringJointParams.m_Length = typed_joint->GetLength() * inv_scale;
                          params.m_SpringJointParams.m_FrequencyHz = typed_joint->GetFrequency();
                          params.m_SpringJointParams.m_DampingRatio = typed_joint->GetDampingRatio();
                      }
                      break;
                  case dmPhysics::JOINT_TYPE_FIXED:

Repository search results · GitHub

britzl · November 3, 2020, 7:16am

From the description it does indeed sound like what you want. Is there an equivalent kind of joint in Bullet?

Pkeod · November 3, 2020, 7:24am

I think btPoint2PointConstraint would be it?

Existing joints don’t work in 3D though, they are only for 2D?

Mathias_Westerdahl · November 3, 2020, 7:46am

We chose the first set of constraints since there were versions of them in 3D as well.

Pkeod · November 3, 2020, 7:55am

What do you think the naming should be for a joint like this?

I’ve made an issue for the feature Add physics.JOINT_TYPE_POINT · Issue #5309 · defold/defold · GitHub

https://storage.googleapis.com/google-code-archive-downloads/v2/code.google.com/bullet/bullet-2.77.zip under demos / opengl / DemoApplication.cpp there is a demo of mouse picking / moving