A physics constraint class implementing a universal joint, ported from Bullet. It builds local frames from given world-space anchor and two orthogonal axes, sets 6DOF limits to restrict linear motion and allow the two rotational degrees, and exposes getters and setters for anchor, axes and angular limits.
/* * C# / XNA port of Bullet (c) 2011 Mark Neale <[email protected]> * * Bullet Continuous Collision Detection and Physics Library * Copyright (c) 2003-2008 Erwin Coumans http://www.bulletphysics.com/ * * This software is provided 'as-is', without any express or implied warranty. * In no event will the authors be held liable for any damages arising from * the use of this software. * * Permission is granted to anyone to use this software for any purpose, * including commercial applications, and to alter it and redistribute it * freely, subject to the following restrictions: * * 1. The origin of this software must not be misrepresented; you must not * claim that you wrote the original software. If you use this software * in a product, an acknowledgment in the product documentation would be * appreciated but is not required. * 2. Altered source versions must be plainly marked as such, and must not be * misrepresented as being the original software. * 3. This notice may not be removed or altered from any source distribution. */ // Adapted from BulletXNA 73b2e1b9: namespace isolation, no XNA rendering, one type per file. #nullable disable #pragma warning disable CS1591, CS0168, CS0219, CS0414, CS0660, CS0661, CS0659, CS0693, CS8981, CS0108, CS0114 using HumanoidRetargeter.Core.Formats.Mmd.Bullet.LinearMath; namespace HumanoidRetargeter.Core.Formats.Mmd.Bullet.BulletDynamics; internal class UniversalConstraint : Generic6DofConstraint { private const float UNIV_EPS = 0.01f; protected IndexedVector3 m_anchor; protected IndexedVector3 m_axis1; protected IndexedVector3 m_axis2; // constructor // anchor, axis1 and axis2 are in world coordinate system // axis1 must be orthogonal to axis2 public UniversalConstraint(RigidBody rbA, RigidBody rbB, ref IndexedVector3 anchor, ref IndexedVector3 axis1, ref IndexedVector3 axis2) : base(rbA, rbB, ref BulletGlobals.IdentityMatrix, ref BulletGlobals.IdentityMatrix, true) { m_anchor = anchor; m_axis1 = axis1; m_axis2 = axis2; // build frame basis // 6DOF constraint uses Euler angles and to define limits // it is assumed that rotational order is : // Z - first, allowed limits are (-PI,PI); // new position of Y - second (allowed limits are (-PI/2 + epsilon, PI/2 - epsilon), where epsilon is a small positive number // used to prevent constraint from instability on poles; // new position of X, allowed limits are (-PI,PI); // So to simulate ODE Universal joint we should use parent axis as Z, child axis as Y and limit all other DOFs // Build the frame in world coordinate system first IndexedVector3 zAxis = IndexedVector3.Normalize(m_axis1); IndexedVector3 yAxis = IndexedVector3.Normalize(m_axis2); IndexedVector3 xAxis = IndexedVector3.Cross(yAxis, zAxis); // we want right coordinate system IndexedMatrix frameInW = IndexedMatrix.Identity; frameInW._basis = new IndexedBasisMatrix(xAxis.X, yAxis.X, zAxis.X, xAxis.Y, yAxis.Y, zAxis.Y, xAxis.Z, yAxis.Z, zAxis.Z); frameInW._origin = anchor; // now get constraint frame in local coordinate systems //m_frameInA = MathUtil.inverseTimes(rbA.getCenterOfMassTransform(),frameInW); //m_frameInB = MathUtil.inverseTimes(rbB.getCenterOfMassTransform(),frameInW); m_frameInA = rbA.GetCenterOfMassTransform().Inverse() * frameInW; m_frameInB = rbB.GetCenterOfMassTransform().Inverse() * frameInW; // sei limits SetLinearLowerLimit(IndexedVector3.Zero); SetLinearUpperLimit(IndexedVector3.Zero); SetAngularLowerLimit(new IndexedVector3(0.0f, -MathUtil.SIMD_HALF_PI + UNIV_EPS, -MathUtil.SIMD_PI + UNIV_EPS)); SetAngularUpperLimit(new IndexedVector3(0.0f, MathUtil.SIMD_HALF_PI - UNIV_EPS, MathUtil.SIMD_PI - UNIV_EPS)); } // access public IndexedVector3 GetAnchor() { return m_calculatedTransformA._origin; } public IndexedVector3 GetAnchor2() { return m_calculatedTransformB._origin; } public IndexedVector3 GetAxis1() { return m_axis1; } public IndexedVector3 GetAxis2() { return m_axis2; } public float GetAngle1() { return GetAngle(2); } public float GetAngle2() { return GetAngle(1); } // limits public void SetUpperLimit(float ang1max, float ang2max) { SetAngularUpperLimit(new IndexedVector3(0.0f, ang1max, ang2max)); } public void SetLowerLimit(float ang1min, float ang2min) { SetAngularLowerLimit(new IndexedVector3(0.0f, ang1min, ang2min)); } public override void SetAxis(ref IndexedVector3 axis1, ref IndexedVector3 axis2) { IndexedVector3 zAxis = IndexedVector3.Normalize(axis1); IndexedVector3 yAxis = IndexedVector3.Normalize(axis2); IndexedVector3 xAxis = IndexedVector3.Cross(yAxis, zAxis); // we want right coordinate system IndexedMatrix frameInW = IndexedMatrix.Identity; frameInW._basis = new IndexedBasisMatrix(xAxis.X, yAxis.X, zAxis.X, xAxis.Y, yAxis.Y, zAxis.Y, xAxis.Z, yAxis.Z, zAxis.Z); // now get constraint frame in local coordinate systems m_frameInA = m_rbA.GetCenterOfMassTransform().Inverse() * frameInW; m_frameInB = m_rbB.GetCenterOfMassTransform().Inverse() * frameInW; CalculateTransforms(); } }