fix uninitialized variable in btMultiBody

use btAssert to detect 0 determinant in btMatrix3x3 inverse
Remove obsolete comment in PosixSharedMemory, the Windows shared memory implementation was done over a year ago

examples/OpenGLWindow/SimpleOpenGL3App.cpp

@@ -172,7 +172,7 @@ SimpleOpenGL3App::SimpleOpenGL3App(	const char* title, int width,int height, boo
     
     b3Assert(glGetError() ==GL_NO_ERROR);
 
-	m_instancingRenderer = new GLInstancingRenderer(128*1024,64*1024*1024);
+	m_instancingRenderer = new GLInstancingRenderer(128*1024,128*1024*1024);
     m_primRenderer = new GLPrimitiveRenderer(width,height);
     
     m_renderer = m_instancingRenderer ;

examples/SharedMemory/PosixSharedMemory.cpp

@@ -2,7 +2,7 @@
 #include "Bullet3Common/b3Logging.h"
 #include "LinearMath/btScalar.h" //for btAssert
 
-//haven't implemented shared memory on Windows yet, just Linux and Mac
+//Windows implementation is in Win32SharedMemory.cpp
 #ifndef _WIN32
 #define TEST_SHARED_MEMORY
 #endif//_WIN32

src/BulletDynamics/Featherstone/btMultiBody.cpp

@@ -122,10 +122,15 @@ btMultiBody::btMultiBody(int n_links,
 		m_useGlobalVelocities(false),
 		m_internalNeedsJointFeedback(false)
 {
+	m_cachedInertiaTopLeft.setValue(0,0,0,0,0,0,0,0,0);
+	m_cachedInertiaTopRight.setValue(0,0,0,0,0,0,0,0,0);
+	m_cachedInertiaLowerLeft.setValue(0,0,0,0,0,0,0,0,0);
+	m_cachedInertiaLowerRight.setValue(0,0,0,0,0,0,0,0,0);
+	m_cachedInertiaValid=false;
+
 	m_links.resize(n_links);
 	m_matrixBuf.resize(n_links + 1);
 
-
     m_baseForce.setValue(0, 0, 0);
     m_baseTorque.setValue(0, 0, 0);
 }
@@ -1012,6 +1017,7 @@ void btMultiBody::computeAccelerationsArticulatedBodyAlgorithmMultiDof(btScalar
 	{
         if (num_links > 0) 
 		{
+			m_cachedInertiaValid = true;
 			m_cachedInertiaTopLeft = spatInertia[0].m_topLeftMat;
 			m_cachedInertiaTopRight = spatInertia[0].m_topRightMat;
 			m_cachedInertiaLowerLeft = spatInertia[0].m_bottomLeftMat;
@@ -1215,6 +1221,14 @@ void btMultiBody::solveImatrix(const btVector3& rhs_top, const btVector3& rhs_bo
         result[5] = rhs_top[2] / m_baseMass;
     } else 
 	{
+		if (!m_cachedInertiaValid)
+		{
+			for (int i=0;i<6;i++)
+			{
+				result[i] = 0.f;
+			}
+			return;
+		}
 		/// Special routine for calculating the inverse of a spatial inertia matrix
 		///the 6x6 matrix is stored as 4 blocks of 3x3 matrices
 		btMatrix3x3 Binv = m_cachedInertiaTopRight.inverse()*-1.f;
@@ -1261,6 +1275,13 @@ void btMultiBody::solveImatrix(const btSpatialForceVector &rhs, btSpatialMotionV
 	{
 		/// Special routine for calculating the inverse of a spatial inertia matrix
 		///the 6x6 matrix is stored as 4 blocks of 3x3 matrices
+		if (!m_cachedInertiaValid)
+		{
+			result.setLinear(btVector3(0,0,0));
+			result.setAngular(btVector3(0,0,0));
+			result.setVector(btVector3(0,0,0),btVector3(0,0,0));
+			return;
+		}
 		btMatrix3x3 Binv = m_cachedInertiaTopRight.inverse()*-1.f;
 		btMatrix3x3 tmp = m_cachedInertiaLowerRight * Binv;
 		btMatrix3x3 invIupper_right = (tmp * m_cachedInertiaTopLeft + m_cachedInertiaLowerLeft).inverse();

src/BulletDynamics/Featherstone/btMultiBody.h

@@ -677,6 +677,7 @@ private:
 	btMatrix3x3 m_cachedInertiaTopRight;
 	btMatrix3x3 m_cachedInertiaLowerLeft;
 	btMatrix3x3 m_cachedInertiaLowerRight;
+	bool m_cachedInertiaValid;
 
     bool m_fixedBase;
 

src/LinearMath/btMatrix3x3.h

@@ -1047,7 +1047,8 @@ btMatrix3x3::inverse() const
 {
 	btVector3 co(cofac(1, 1, 2, 2), cofac(1, 2, 2, 0), cofac(1, 0, 2, 1));
 	btScalar det = (*this)[0].dot(co);
-	btFullAssert(det != btScalar(0.0));
+	//btFullAssert(det != btScalar(0.0));
+	btAssert(det != btScalar(0.0));
 	btScalar s = btScalar(1.0) / det;
 	return btMatrix3x3(co.x() * s, cofac(0, 2, 2, 1) * s, cofac(0, 1, 1, 2) * s,
 		co.y() * s, cofac(0, 0, 2, 2) * s, cofac(0, 2, 1, 0) * s,