Exemple #1
0
        /// <summary>This returns true if the position errors are within tolerance, allowing an early exit from the iteration loop.</summary>
        /// <param name="positions">The positions of the related bodies.</param>
        /// <returns>
        ///     <c>true</c> if the position errors are within tolerance.
        /// </returns>
        internal override bool SolvePositionConstraints(Position[] positions)
        {
            var cA = positions[_tmp.IndexA].Point;
            var aA = positions[_tmp.IndexA].Angle;
            var cB = positions[_tmp.IndexB].Point;
            var aB = positions[_tmp.IndexB].Angle;

            var qA = new Rotation(aA);
            var qB = new Rotation(aB);

            var mA = _tmp.InverseMassA;
            var mB = _tmp.InverseMassB;
            var iA = _tmp.InverseInertiaA;
            var iB = _tmp.InverseInertiaB;

            // Compute fresh Jacobians
            var rA = qA * (_localAnchorA - _tmp.LocalCenterA);
            var rB = qB * (_localAnchorB - _tmp.LocalCenterB);
// ReSharper disable RedundantCast Necessary for FarPhysics.
            var d = (Vector2)(cB - cA) + (rB - rA);
// ReSharper restore RedundantCast

            var axis = qA * _localXAxisA;
            var a1   = Vector2Util.Cross(d + rA, axis);
            var a2   = Vector2Util.Cross(rB, axis);
            var perp = qA * _localYAxisA;

            var s1 = Vector2Util.Cross(d + rA, perp);
            var s2 = Vector2Util.Cross(rB, perp);

            Vector3 impulse;
            Vector2 c1;

            c1.X = Vector2Util.Dot(ref perp, ref d);
            c1.Y = aB - aA - _referenceAngle;

            var linearError  = System.Math.Abs(c1.X);
            var angularError = System.Math.Abs(c1.Y);

            var active = false;
            var c2     = 0.0f;

            if (_enableLimit)
            {
                var translation = Vector2Util.Dot(ref axis, ref d);
                if (System.Math.Abs(_upperTranslation - _lowerTranslation) < 2.0f * Settings.LinearSlop)
                {
                    // Prevent large angular corrections
                    c2          = MathHelper.Clamp(translation, -Settings.MaxLinearCorrection, Settings.MaxLinearCorrection);
                    linearError = System.Math.Max(linearError, System.Math.Abs(translation));
                    active      = true;
                }
                else if (translation <= _lowerTranslation)
                {
                    // Prevent large linear corrections and allow some slop.
                    c2 = MathHelper.Clamp(
                        translation - _lowerTranslation + Settings.LinearSlop,
                        -Settings.MaxLinearCorrection,
                        0.0f);
                    linearError = System.Math.Max(linearError, _lowerTranslation - translation);
                    active      = true;
                }
                else if (translation >= _upperTranslation)
                {
                    // Prevent large linear corrections and allow some slop.
                    c2 = MathHelper.Clamp(
                        translation - _upperTranslation - Settings.LinearSlop,
                        0.0f,
                        Settings.MaxLinearCorrection);
                    linearError = System.Math.Max(linearError, translation - _upperTranslation);
                    active      = true;
                }
            }

            if (active)
            {
                var k11 = mA + mB + iA * s1 * s1 + iB * s2 * s2;
                var k12 = iA * s1 + iB * s2;
                var k13 = iA * s1 * a1 + iB * s2 * a2;
                var k22 = iA + iB;
// ReSharper disable CompareOfFloatsByEqualityOperator Intentional.
                if (k22 == 0.0f)
// ReSharper restore CompareOfFloatsByEqualityOperator
                {
                    // For fixed rotation
                    k22 = 1.0f;
                }
                var k23 = iA * a1 + iB * a2;
                var k33 = mA + mB + iA * a1 * a1 + iB * a2 * a2;

                Matrix33 k;
                Vector3Util.Set(out k.Column1, k11, k12, k13);
                Vector3Util.Set(out k.Column2, k12, k22, k23);
                Vector3Util.Set(out k.Column3, k13, k23, k33);

                Vector3 c;
                c.X = c1.X;
                c.Y = c1.Y;
                c.Z = c2;

                impulse = k.Solve33(-c);
            }
            else
            {
                var k11 = mA + mB + iA * s1 * s1 + iB * s2 * s2;
                var k12 = iA * s1 + iB * s2;
                var k22 = iA + iB;
// ReSharper disable CompareOfFloatsByEqualityOperator Intentional.
                if (k22 == 0.0f)
// ReSharper restore CompareOfFloatsByEqualityOperator
                {
                    k22 = 1.0f;
                }

                Matrix22 k;
                Vector2Util.Set(out k.Column1, k11, k12);
                Vector2Util.Set(out k.Column2, k12, k22);

                var impulse1 = k.Solve(-c1);
                impulse.X = impulse1.X;
                impulse.Y = impulse1.Y;
                impulse.Z = 0.0f;
            }

            var p  = impulse.X * perp + impulse.Z * axis;
            var lA = impulse.X * s1 + impulse.Y + impulse.Z * a1;
            var lB = impulse.X * s2 + impulse.Y + impulse.Z * a2;

            cA -= mA * p;
            aA -= iA * lA;
            cB += mB * p;
            aB += iB * lB;

            positions[_tmp.IndexA].Point = cA;
            positions[_tmp.IndexA].Angle = aA;
            positions[_tmp.IndexB].Point = cB;
            positions[_tmp.IndexB].Angle = aB;

            return(linearError <= (Settings.LinearSlop + Settings.Epsilon) && angularError <= (Settings.AngularSlop + Settings.Epsilon));
        }