prevent twist limits being created with equal lower and upper limits

Signed-off-by: greerdv <greerdv@amazon.com>

Gems/PhysX/Code/Source/Joint/PhysXJointUtils.cpp

@@ -224,8 +224,22 @@ namespace PhysX {
                 physx::PxJointLimitCone limitCone(swingLimitY, swingLimitZ);
                 joint->setSwingLimit(limitCone);
 
-                const float twistLower = AZ::DegToRad(AZStd::GetMin(configuration.m_twistLimitLower, configuration.m_twistLimitUpper));
+                float twistLower = AZ::DegToRad(AZStd::GetMin(configuration.m_twistLimitLower, configuration.m_twistLimitUpper));
-                const float twistUpper = AZ::DegToRad(AZStd::GetMax(configuration.m_twistLimitLower, configuration.m_twistLimitUpper));
+                float twistUpper = AZ::DegToRad(AZStd::GetMax(configuration.m_twistLimitLower, configuration.m_twistLimitUpper));
+                // make sure there is at least a small difference between the lower and upper limits to avoid problems in PhysX
+                const float minSwingLimitRangeRadians = AZ::DegToRad(JointConstants::MinTwistLimitRangeDegrees);
+                if (const float twistLimitRange = twistUpper - twistLower;
+                    twistLimitRange < minSwingLimitRangeRadians)
+                {
+                    if (twistUpper > 0.0f)
+                    {
+                        twistLower -= (minSwingLimitRangeRadians - twistLimitRange);
+                    }
+                    else
+                    {
+                        twistUpper += (minSwingLimitRangeRadians - twistLimitRange);
+                    }
+                }
                 physx::PxJointAngularLimitPair twistLimitPair(twistLower, twistUpper);
                 joint->setTwistLimit(twistLimitPair);
 

Gems/PhysX/Code/Source/Joint/PhysXJointUtils.h

@@ -18,9 +18,11 @@ namespace PhysX
 {
     namespace JointConstants
     {
-        // Setting swing limits to very small values can cause extreme stability problems, so clamp above a small
+        // Setting joint limits to very small values can cause extreme stability problems, so clamp above a small
         // threshold.
         static const float MinSwingLimitDegrees = 1.0f;
+        // Minimum range between lower and upper twist limits.
+        static const float MinTwistLimitRangeDegrees = 1.0f;
     } // namespace JointConstants
 
     namespace Utils