MJCF: support for default joint limited="true"

examples/Importers/ImportMJCFDemo/BulletMJCFImporter.cpp

@@ -152,6 +152,9 @@ struct BulletMJCFImporterInternalData
 	int m_defaultCollisionMask;
 	btScalar m_defaultCollisionMargin;
 
+	// joint defaults
+	std::string m_defaultJointLimited;
+
 	//those collision shapes are deleted by caller (todo: make sure this happens!)
 	btAlignedObjectArray<btCollisionShape*> m_allocatedCollisionShapes;
 
@@ -243,6 +246,17 @@ struct BulletMJCFImporterInternalData
 			{
 				parseAssets(child_xml,logger);
 			}
+			if (n=="joint")
+			{
+				// Other attributes here:
+				// armature="1"
+				// damping="1"
+				// limited="true"
+				if (const char* conTypeStr = child_xml->Attribute("limited"))
+				{
+					m_defaultJointLimited = child_xml->Attribute("limited");
+				}
+			}
 			if (n=="geom")
 			{
 				//contype, conaffinity 
@@ -366,9 +380,11 @@ struct BulletMJCFImporterInternalData
 		bool isLimited = false;
 		double range[2] = {1,0};
 
+		std::string lim = m_defaultJointLimited;
 		if (limitedStr)
 		{
-			std::string lim = limitedStr;
+			lim = limitedStr;
+		}
 		if (lim=="true")
 		{
 			isLimited = true;
@@ -387,18 +403,34 @@ struct BulletMJCFImporterInternalData
 			}
 			if (sizes.size()==2)
 			{
-					range[0] = sizes[0];
+				// TODO angle units are in "<compiler angle="degree" inertiafromgeom="true"/>
-					range[1] = sizes[1];
+				range[0] = sizes[0] * M_PI / 180;
+				range[1] = sizes[1] * M_PI / 180;
 			} else
 			{
 				logger->reportWarning("Expected range[2] in joint with limits");
 			}
+		}
 
-			}
+		// TODO armature : real, "0" Armature inertia (or rotor inertia) of all
-		} else
+		// degrees of freedom created by this joint. These are constants added to the
-		{
+		// diagonal of the inertia matrix in generalized coordinates. They make the
-//			logger->reportWarning("joint without limited field");
+		// simulation more stable, and often increase physical realism. This is because
-		}
+		// when a motor is attached to the system with a transmission that amplifies
+		// the motor force by c, the inertia of the rotor (i.e. the moving part of the
+		// motor) is amplified by c*c. The same holds for gears in the early stages of
+		// planetary gear boxes. These extra inertias often dominate the inertias of
+		// the robot parts that are represented explicitly in the model, and the
+		// armature attribute is the way to model them.
+
+		// TODO damping : real, "0" Damping applied to all degrees of
+		// freedom created by this joint. Unlike friction loss
+		// which is computed by the constraint solver, damping is
+		// simply a force linear in velocity. It is included in
+		// the passive forces. Despite this simplicity, larger
+		// damping values can make numerical integrators unstable,
+		// which is why our Euler integrator handles damping
+		// implicitly. See Integration in the Computation chapter.
 
 		bool jointHandled = false;
 		const UrdfLink* linkPtr = getLink(modelIndex,linkIndex);