[InverseDynamics] Add custom namespaces per configuration

BulletInverseDynamics can be configured to compile using Eigen
instead of Bullet's LinearMath.

Adds a preprocessor defined specific namespace for each
configuration to produce linker errors if incompatible
libraries are linked (eg, builtin core library and
utilities for bullet types).

src/BulletInverseDynamics/IDConfig.hpp

@@ -24,7 +24,11 @@
 #define INVDYN_INCLUDE_HELPER_2(x) #x
 #define INVDYN_INCLUDE_HELPER(x) INVDYN_INCLUDE_HELPER_2(x)
 #include INVDYN_INCLUDE_HELPER(BT_CUSTOM_INVERSE_DYNAMICS_CONFIG_H)
+#ifndef btInverseDynamics 
+#error "custom inverse dynamics config, but no custom namespace defined"
+#endif
 #else
+#define btInverseDynamics btInverseDynamicsBullet3
 // Use default configuration with bullet's types
 // Use the same scalar type as rest of bullet library
 #include "LinearMath/btScalar.h"

src/BulletInverseDynamics/IDConfigBuiltin.hpp

@@ -1,6 +1,7 @@
 ///@file Configuration for Inverse Dynamics Library without external dependencies
 #ifndef INVDYNCONFIG_BUILTIN_HPP_
 #define INVDYNCONFIG_BUILTIN_HPP_
+#define btInverseDynamics btInverseDynamicsBuiltin
 #ifdef BT_USE_DOUBLE_PRECISION
 // choose double/single precision version
 typedef double idScalar;

src/BulletInverseDynamics/IDConfigEigen.hpp

@@ -1,6 +1,7 @@
 ///@file Configuration for Inverse Dynamics Library with Eigen
 #ifndef INVDYNCONFIG_EIGEN_HPP_
 #define INVDYNCONFIG_EIGEN_HPP_
+#define btInverseDynamics btInverseDynamicsEigen
 #ifdef BT_USE_DOUBLE_PRECISION
 // choose double/single precision version
 typedef double idScalar;

src/BulletInverseDynamics/MultiBodyTree.hpp

@@ -1,6 +1,7 @@
 #ifndef MULTIBODYTREE_HPP_
 #define MULTIBODYTREE_HPP_
 
+#include "IDConfig.hpp"
 #include "IDMath.hpp"
 
 namespace btInverseDynamics {
@@ -304,5 +305,4 @@ private:
     InitCache* m_init_cache;
 };
 }  // namespace btInverseDynamics
-
 #endif  // MULTIBODYTREE_HPP_

src/BulletInverseDynamics/details/IDMatVec.hpp

@@ -4,6 +4,8 @@
 
 #include <cstdlib>
 
+#include "../IDConfig.hpp"
+
 namespace btInverseDynamics {
 class vec3;
 class vecx;