content: /*
   * FXGL - JavaFX Game Library. The MIT License (MIT).
   * Copyright (c) AlmasB (almaslvl@gmail.com).
   * See LICENSE for details.
   */
  package com.almasb.fxgl.physics.box2d.dynamics.joints;
  
  import com.almasb.fxgl.core.math.FXGLMath;
  import com.almasb.fxgl.core.math.Vec2;
  import com.almasb.fxgl.core.math.Vec3;
  import com.almasb.fxgl.physics.box2d.common.JBoxSettings;
  import com.almasb.fxgl.physics.box2d.common.Mat22;
  import com.almasb.fxgl.physics.box2d.common.Mat33;
  import com.almasb.fxgl.physics.box2d.common.Rotation;
  import com.almasb.fxgl.physics.box2d.dynamics.Body;
  import com.almasb.fxgl.physics.box2d.dynamics.SolverData;
  import com.almasb.fxgl.physics.box2d.pooling.IWorldPool;
  
  //Point-to-point constraint
  //C = p2 - p1
  //Cdot = v2 - v1
  //   = v2 + cross(w2, r2) - v1 - cross(w1, r1)
  //J = [-I -r1_skew I r2_skew ]
  //Identity used:
  //w k % (rx i + ry j) = w * (-ry i + rx j)
  
  //Motor constraint
  //Cdot = w2 - w1
  //J = [0 0 -1 0 0 1]
  //K = invI1 + invI2
  
  /**
   * A revolute joint constrains two bodies to share a common point while they are free to rotate
   * about the point. The relative rotation about the shared point is the joint angle. You can limit
   * the relative rotation with a joint limit that specifies a lower and upper angle. You can use a
   * motor to drive the relative rotation about the shared point. A maximum motor torque is provided
   * so that infinite forces are not generated.
   *
   * @author Daniel Murphy
   */
  public final class RevoluteJoint extends Joint {
  
      // Solver shared
      final Vec2 m_localAnchorA = new Vec2();
      final Vec2 m_localAnchorB = new Vec2();
      private final Vec3 m_impulse = new Vec3();
      private float m_motorImpulse;
  
      private boolean m_enableMotor;
      private float m_maxMotorTorque;
      private float m_motorSpeed;
  
      private boolean m_enableLimit;
      private float m_referenceAngle;
      private float m_lowerAngle;
      private float m_upperAngle;
  
      // Solver temp
      private int m_indexA;
      private int m_indexB;
      private final Vec2 m_rA = new Vec2();
      private final Vec2 m_rB = new Vec2();
      private final Vec2 m_localCenterA = new Vec2();
      private final Vec2 m_localCenterB = new Vec2();
      private float m_invMassA;
      private float m_invMassB;
      private float m_invIA;
      private float m_invIB;
      private final Mat33 m_mass = new Mat33(); // effective mass for point-to-point constraint.
      private float m_motorMass; // effective mass for motor/limit angular constraint.
      private LimitState m_limitState;
  
      RevoluteJoint(IWorldPool argWorld, RevoluteJointDef def) {
          super(argWorld, def);
          m_localAnchorA.set(def.localAnchorA);
          m_localAnchorB.set(def.localAnchorB);
          m_referenceAngle = def.referenceAngle;
  
          m_motorImpulse = 0;
  
          m_lowerAngle = def.lowerAngle;
          m_upperAngle = def.upperAngle;
          m_maxMotorTorque = def.maxMotorTorque;
          m_motorSpeed = def.motorSpeed;
          m_enableLimit = def.enableLimit;
          m_enableMotor = def.enableMotor;
          m_limitState = LimitState.INACTIVE;
      }
  
      @Override
      public void initVelocityConstraints(final SolverData data) {
          m_indexA = m_bodyA.m_islandIndex;
          m_indexB = m_bodyB.m_islandIndex;
          m_localCenterA.set(m_bodyA.m_sweep.localCenter);
          m_localCenterB.set(m_bodyB.m_sweep.localCenter);
          m_invMassA = m_bodyA.m_invMass;
          m_invMassB = m_bodyB.m_invMass;
          m_invIA = m_bodyA.m_invI;
          m_invIB = m_bodyB.m_invI;
  
          // Vec2 cA = data.positions[m_indexA].c;
          float aA = data.positions[m_indexA].a;
          Vec2 vA = data.velocities[m_indexA].v;
          float wA = data.velocities[m_indexA].w;
  
          // Vec2 cB = data.positions[m_indexB].c;
          float aB = data.positions[m_indexB].a;
          Vec2 vB = data.velocities[m_indexB].v;
          float wB = data.velocities[m_indexB].w;
          final Rotation qA = pool.popRot();
          final Rotation qB = pool.popRot();
          final Vec2 temp = pool.popVec2();
  
          qA.set(aA);
          qB.set(aB);
  
          // Compute the effective masses.
          Rotation.mulToOutUnsafe(qA, temp.set(m_localAnchorA).subLocal(m_localCenterA), m_rA);
          Rotation.mulToOutUnsafe(qB, temp.set(m_localAnchorB).subLocal(m_localCenterB), m_rB);
  
          // J = [-I -r1_skew I r2_skew]
          // [ 0 -1 0 1]
          // r_skew = [-ry; rx]
  
          // Matlab
          // K = [ mA+r1y^2*iA+mB+r2y^2*iB, -r1y*iA*r1x-r2y*iB*r2x, -r1y*iA-r2y*iB]
          // [ -r1y*iA*r1x-r2y*iB*r2x, mA+r1x^2*iA+mB+r2x^2*iB, r1x*iA+r2x*iB]
          // [ -r1y*iA-r2y*iB, r1x*iA+r2x*iB, iA+iB]
  
          float mA = m_invMassA, mB = m_invMassB;
          float iA = m_invIA, iB = m_invIB;
  
          boolean fixedRotation = iA + iB == 0.0f;
  
          m_mass.ex.x = mA + mB + m_rA.y * m_rA.y * iA + m_rB.y * m_rB.y * iB;
          m_mass.ey.x = -m_rA.y * m_rA.x * iA - m_rB.y * m_rB.x * iB;
          m_mass.ez.x = -m_rA.y * iA - m_rB.y * iB;
          m_mass.ex.y = m_mass.ey.x;
          m_mass.ey.y = mA + mB + m_rA.x * m_rA.x * iA + m_rB.x * m_rB.x * iB;
          m_mass.ez.y = m_rA.x * iA + m_rB.x * iB;
          m_mass.ex.z = m_mass.ez.x;
          m_mass.ey.z = m_mass.ez.y;
          m_mass.ez.z = iA + iB;
  
          m_motorMass = iA + iB;
          if (m_motorMass > 0.0f) {
              m_motorMass = 1.0f / m_motorMass;
          }
  
          if (!m_enableMotor || fixedRotation) {
              m_motorImpulse = 0.0f;
          }
  
          if (m_enableLimit && !fixedRotation) {
              float jointAngle = aB - aA - m_referenceAngle;
              if (FXGLMath.abs(m_upperAngle - m_lowerAngle) < 2.0f * JBoxSettings.angularSlop) {
                  m_limitState = LimitState.EQUAL;
              } else if (jointAngle <= m_lowerAngle) {
                  if (m_limitState != LimitState.AT_LOWER) {
                      m_impulse.z = 0.0f;
                  }
                  m_limitState = LimitState.AT_LOWER;
              } else if (jointAngle >= m_upperAngle) {
                  if (m_limitState != LimitState.AT_UPPER) {
                      m_impulse.z = 0.0f;
                  }
                  m_limitState = LimitState.AT_UPPER;
              } else {
                  m_limitState = LimitState.INACTIVE;
                  m_impulse.z = 0.0f;
              }
          } else {
              m_limitState = LimitState.INACTIVE;
          }
  
          if (data.step.warmStarting) {
              final Vec2 P = pool.popVec2();
              // Scale impulses to support a variable time step.
              m_impulse.x *= data.step.dtRatio;
              m_impulse.y *= data.step.dtRatio;
              m_motorImpulse *= data.step.dtRatio;
  
              P.x = m_impulse.x;
              P.y = m_impulse.y;
  
              vA.x -= mA * P.x;
              vA.y -= mA * P.y;
              wA -= iA * (Vec2.cross(m_rA, P) + m_motorImpulse + m_impulse.z);
  
              vB.x += mB * P.x;
              vB.y += mB * P.y;
              wB += iB * (Vec2.cross(m_rB, P) + m_motorImpulse + m_impulse.z);
              pool.pushVec2(1);
          } else {
              m_impulse.setZero();
              m_motorImpulse = 0.0f;
          }
          // data.velocities[m_indexA].v.set(vA);
          data.velocities[m_indexA].w = wA;
          // data.velocities[m_indexB].v.set(vB);
          data.velocities[m_indexB].w = wB;
  
          pool.pushVec2(1);
          pool.pushRot(2);
      }
  
      @Override
      public void solveVelocityConstraints(final SolverData data) {
          Vec2 vA = data.velocities[m_indexA].v;
          float wA = data.velocities[m_indexA].w;
          Vec2 vB = data.velocities[m_indexB].v;
          float wB = data.velocities[m_indexB].w;
  
          float mA = m_invMassA, mB = m_invMassB;
          float iA = m_invIA, iB = m_invIB;
  
          boolean fixedRotation = iA + iB == 0.0f;
  
          // Solve motor constraint.
          if (m_enableMotor && m_limitState != LimitState.EQUAL && !fixedRotation) {
              float Cdot = wB - wA - m_motorSpeed;
              float impulse = -m_motorMass * Cdot;
              float oldImpulse = m_motorImpulse;
              float maxImpulse = data.step.dt * m_maxMotorTorque;
              m_motorImpulse = FXGLMath.clamp(m_motorImpulse + impulse, -maxImpulse, maxImpulse);
              impulse = m_motorImpulse - oldImpulse;
  
              wA -= iA * impulse;
              wB += iB * impulse;
          }
          final Vec2 temp = pool.popVec2();
  
          // Solve limit constraint.
          if (m_enableLimit && m_limitState != LimitState.INACTIVE && !fixedRotation) {
  
              final Vec2 Cdot1 = pool.popVec2();
              final Vec3 Cdot = pool.popVec3();
  
              // Solve point-to-point constraint
              Vec2.crossToOutUnsafe(wA, m_rA, temp);
              Vec2.crossToOutUnsafe(wB, m_rB, Cdot1);
              Cdot1.addLocal(vB).subLocal(vA).subLocal(temp);
              float Cdot2 = wB - wA;
              Cdot.set(Cdot1.x, Cdot1.y, Cdot2);
  
              Vec3 impulse = pool.popVec3();
              m_mass.solve33ToOut(Cdot, impulse);
              impulse.negateLocal();
  
              if (m_limitState == LimitState.EQUAL) {
                  m_impulse.addLocal(impulse);
              } else if (m_limitState == LimitState.AT_LOWER) {
                  float newImpulse = m_impulse.z + impulse.z;
                  if (newImpulse < 0.0f) {
                      final Vec2 rhs = pool.popVec2();
                      rhs.set(m_mass.ez.x, m_mass.ez.y).mulLocal(m_impulse.z).subLocal(Cdot1);
                      m_mass.solve22ToOut(rhs, temp);
                      impulse.x = temp.x;
                      impulse.y = temp.y;
                      impulse.z = -m_impulse.z;
                      m_impulse.x += temp.x;
                      m_impulse.y += temp.y;
                      m_impulse.z = 0.0f;
                      pool.pushVec2(1);
                  } else {
                      m_impulse.addLocal(impulse);
                  }
              } else if (m_limitState == LimitState.AT_UPPER) {
                  float newImpulse = m_impulse.z + impulse.z;
                  if (newImpulse > 0.0f) {
                      final Vec2 rhs = pool.popVec2();
                      rhs.set(m_mass.ez.x, m_mass.ez.y).mulLocal(m_impulse.z).subLocal(Cdot1);
                      m_mass.solve22ToOut(rhs, temp);
                      impulse.x = temp.x;
                      impulse.y = temp.y;
                      impulse.z = -m_impulse.z;
                      m_impulse.x += temp.x;
                      m_impulse.y += temp.y;
                      m_impulse.z = 0.0f;
                      pool.pushVec2(1);
                  } else {
                      m_impulse.addLocal(impulse);
                  }
              }
              final Vec2 P = pool.popVec2();
  
              P.set(impulse.x, impulse.y);
  
              vA.x -= mA * P.x;
              vA.y -= mA * P.y;
              wA -= iA * (Vec2.cross(m_rA, P) + impulse.z);
  
              vB.x += mB * P.x;
              vB.y += mB * P.y;
              wB += iB * (Vec2.cross(m_rB, P) + impulse.z);
  
              pool.pushVec2(2);
              pool.pushVec3(2);
          } else {
  
              // Solve point-to-point constraint
              Vec2 Cdot = pool.popVec2();
              Vec2 impulse = pool.popVec2();
  
              Vec2.crossToOutUnsafe(wA, m_rA, temp);
              Vec2.crossToOutUnsafe(wB, m_rB, Cdot);
              Cdot.addLocal(vB).subLocal(vA).subLocal(temp);
              m_mass.solve22ToOut(Cdot.negateLocal(), impulse); // just leave negated
  
              m_impulse.x += impulse.x;
              m_impulse.y += impulse.y;
  
              vA.x -= mA * impulse.x;
              vA.y -= mA * impulse.y;
              wA -= iA * Vec2.cross(m_rA, impulse);
  
              vB.x += mB * impulse.x;
              vB.y += mB * impulse.y;
              wB += iB * Vec2.cross(m_rB, impulse);
  
              pool.pushVec2(2);
          }
  
          // data.velocities[m_indexA].v.set(vA);
          data.velocities[m_indexA].w = wA;
          // data.velocities[m_indexB].v.set(vB);
          data.velocities[m_indexB].w = wB;
  
          pool.pushVec2(1);
      }
  
      @Override
      public boolean solvePositionConstraints(final SolverData data) {
          final Rotation qA = pool.popRot();
          final Rotation qB = pool.popRot();
          Vec2 cA = data.positions[m_indexA].c;
          float aA = data.positions[m_indexA].a;
          Vec2 cB = data.positions[m_indexB].c;
          float aB = data.positions[m_indexB].a;
  
          qA.set(aA);
          qB.set(aB);
  
          float angularError = 0.0f;
          float positionError = 0.0f;
  
          boolean fixedRotation = m_invIA + m_invIB == 0.0f;
  
          // Solve angular limit constraint.
          if (m_enableLimit && m_limitState != LimitState.INACTIVE && !fixedRotation) {
              float angle = aB - aA - m_referenceAngle;
              float limitImpulse = 0.0f;
  
              if (m_limitState == LimitState.EQUAL) {
                  // Prevent large angular corrections
                  float C =
                          FXGLMath.clamp(angle - m_lowerAngle, -JBoxSettings.maxAngularCorrection,
                                  JBoxSettings.maxAngularCorrection);
                  limitImpulse = -m_motorMass * C;
                  angularError = FXGLMath.abs(C);
              } else if (m_limitState == LimitState.AT_LOWER) {
                  float C = angle - m_lowerAngle;
                  angularError = -C;
  
                  // Prevent large angular corrections and allow some slop.
                  C = FXGLMath.clamp(C + JBoxSettings.angularSlop, -JBoxSettings.maxAngularCorrection, 0.0f);
                  limitImpulse = -m_motorMass * C;
              } else if (m_limitState == LimitState.AT_UPPER) {
                  float C = angle - m_upperAngle;
                  angularError = C;
  
                  // Prevent large angular corrections and allow some slop.
                  C = FXGLMath.clamp(C - JBoxSettings.angularSlop, 0.0f, JBoxSettings.maxAngularCorrection);
                  limitImpulse = -m_motorMass * C;
              }
  
              aA -= m_invIA * limitImpulse;
              aB += m_invIB * limitImpulse;
          }
          // Solve point-to-point constraint.
          {
              qA.set(aA);
              qB.set(aB);
  
              final Vec2 rA = pool.popVec2();
              final Vec2 rB = pool.popVec2();
              final Vec2 C = pool.popVec2();
              final Vec2 impulse = pool.popVec2();
  
              Rotation.mulToOutUnsafe(qA, C.set(m_localAnchorA).subLocal(m_localCenterA), rA);
              Rotation.mulToOutUnsafe(qB, C.set(m_localAnchorB).subLocal(m_localCenterB), rB);
              C.set(cB).addLocal(rB).subLocal(cA).subLocal(rA);
              positionError = C.length();
  
              float mA = m_invMassA, mB = m_invMassB;
              float iA = m_invIA, iB = m_invIB;
  
              final Mat22 K = pool.popMat22();
              K.ex.x = mA + mB + iA * rA.y * rA.y + iB * rB.y * rB.y;
              K.ex.y = -iA * rA.x * rA.y - iB * rB.x * rB.y;
              K.ey.x = K.ex.y;
              K.ey.y = mA + mB + iA * rA.x * rA.x + iB * rB.x * rB.x;
              K.solveToOut(C, impulse);
              impulse.negateLocal();
  
              cA.x -= mA * impulse.x;
              cA.y -= mA * impulse.y;
              aA -= iA * Vec2.cross(rA, impulse);
  
              cB.x += mB * impulse.x;
              cB.y += mB * impulse.y;
              aB += iB * Vec2.cross(rB, impulse);
  
              pool.pushVec2(4);
              pool.pushMat22(1);
          }
          // data.positions[m_indexA].c.set(cA);
          data.positions[m_indexA].a = aA;
          // data.positions[m_indexB].c.set(cB);
          data.positions[m_indexB].a = aB;
  
          pool.pushRot(2);
  
          return positionError <= JBoxSettings.linearSlop && angularError <= JBoxSettings.angularSlop;
      }
  
      public Vec2 getLocalAnchorA() {
          return m_localAnchorA;
      }
  
      public Vec2 getLocalAnchorB() {
          return m_localAnchorB;
      }
  
      public float getReferenceAngle() {
          return m_referenceAngle;
      }
  
      @Override
      public void getAnchorA(Vec2 argOut) {
          m_bodyA.getWorldPointToOut(m_localAnchorA, argOut);
      }
  
      @Override
      public void getAnchorB(Vec2 argOut) {
          m_bodyB.getWorldPointToOut(m_localAnchorB, argOut);
      }
  
      @Override
      public void getReactionForce(float inv_dt, Vec2 argOut) {
          argOut.set(m_impulse.x, m_impulse.y).mulLocal(inv_dt);
      }
  
      @Override
      public float getReactionTorque(float inv_dt) {
          return inv_dt * m_impulse.z;
      }
  
      public float getJointAngle() {
          final Body b1 = m_bodyA;
          final Body b2 = m_bodyB;
          return b2.m_sweep.a - b1.m_sweep.a - m_referenceAngle;
      }
  
      public float getJointSpeed() {
          final Body b1 = m_bodyA;
          final Body b2 = m_bodyB;
          return b2.getAngularVelocity() - b1.getAngularVelocity();
      }
  
      public boolean isMotorEnabled() {
          return m_enableMotor;
      }
  
      public void enableMotor(boolean flag) {
          m_bodyA.setAwake(true);
          m_bodyB.setAwake(true);
          m_enableMotor = flag;
      }
  
      public float getMotorTorque(float inv_dt) {
          return m_motorImpulse * inv_dt;
      }
  
      public void setMotorSpeed(final float speed) {
          m_bodyA.setAwake(true);
          m_bodyB.setAwake(true);
          m_motorSpeed = speed;
      }
  
      public void setMaxMotorTorque(final float torque) {
          m_bodyA.setAwake(true);
          m_bodyB.setAwake(true);
          m_maxMotorTorque = torque;
      }
  
      public float getMotorSpeed() {
          return m_motorSpeed;
      }
  
      public float getMaxMotorTorque() {
          return m_maxMotorTorque;
      }
  
      public boolean isLimitEnabled() {
          return m_enableLimit;
      }
  
      public void enableLimit(final boolean flag) {
          if (flag != m_enableLimit) {
              m_bodyA.setAwake(true);
              m_bodyB.setAwake(true);
              m_enableLimit = flag;
              m_impulse.z = 0.0f;
          }
      }
  
      public float getLowerLimit() {
          return m_lowerAngle;
      }
  
      public float getUpperLimit() {
          return m_upperAngle;
      }
  
      public void setLimits(final float lower, final float upper) {
          assert lower <= upper;
          if (lower != m_lowerAngle || upper != m_upperAngle) {
              m_bodyA.setAwake(true);
              m_bodyB.setAwake(true);
              m_impulse.z = 0.0f;
              m_lowerAngle = lower;
              m_upperAngle = upper;
          }
      }
  }
  