Updates to osg::Transform to allow it subclassed more easily.

include/osg/Transform

@@ -31,7 +31,7 @@ class SG_EXPORT Transform : public Group
 
         META_Node(Transform);
 
-        /** Range of type that the Transform can be.*/
+        /** Range of types that the Transform can be.*/
         enum Type
         {
             DYNAMIC,
@@ -49,12 +49,26 @@ class SG_EXPORT Transform : public Group
 
         /** Get the Transform Type.*/
         inline const Type getType() const { return _type; }
+        
+        
+        
+        /** Get the transform's matrix. */
+        inline const Matrix& getMatrix() const { if (_matrixDirty) computeMatrix(); return *_matrix; }
 
-        inline const Matrix& getMatrix() const { return *_matrix; }
 
+        /** Get the inverse of the transform's matrix.
+          * Automatically compute the inverse if it is not up to date. */
+        inline const Matrix& getInverse() const { if (_inverseDirty) computeInverse(); return *_inverse; }
+
+
+        /** Set the transform's matrix.*/
         inline void setMatrix(const Matrix& mat )
         {
             (*_matrix) = mat;
+
+            _matrixDirty = false; // matrix is valid, so no need to compute
+            _inverseDirty = true; // inverse is now invalid, so will need to recompute.
+            
             dirtyBound();
         }
 
@@ -62,6 +76,10 @@ class SG_EXPORT Transform : public Group
         inline void preMult( const Matrix& mat )
         {
             (*_matrix) =  mat * (*_matrix);
+            
+            _matrixDirty = false; // matrix is valid, so no need to compute
+            _inverseDirty = true; // inverse is now invalid, so will need to recompute.
+            
             dirtyBound();
         }
 
@@ -69,6 +87,10 @@ class SG_EXPORT Transform : public Group
         inline void postMult( const Matrix& mat )
         {
             (*_matrix) =  (*_matrix) * mat;
+
+            _matrixDirty = false; // matrix is valid, so no need to compute
+            _inverseDirty = true; // inverse is now invalid, so will need to recompute.
+
             dirtyBound();
         }
     
@@ -76,10 +98,29 @@ class SG_EXPORT Transform : public Group
     
         virtual ~Transform();
         
+        /** Override's Group's computeBound. 
+          * There is no need to override in subclasses from osg::Transform since this computeBound() uses 
+          * the underlying matrix (calling computeMatrix if required.) */
         virtual const bool computeBound() const;
+        
+        /** If you subclass from osg::Transform you must override computeMatrix() to provide your own mechanism for
+          * setting up the 4x4 matrix. An example of a subclass might a PositionAttitudeTransfrom which is its own
+          * Vec3 and Quat to calculate the matrix.*/
+        virtual void computeMatrix() const { _matrixDirty = false; }
 
-        Type            _type;
-        ref_ptr<Matrix> _matrix;
+        /** If you subclass from osg::Transform it is safe to rely on this default implementation which uses osg::Matrix::invert(getMatrix())
+          * to compute the inverse.  However, you may wish to override this method too since there may well be a more optimal way to
+          * compute the inverse rather than rely on the brute force method of osg::Matrix::invert(..).*/
+        virtual void computeInverse() const { if (_inverseDirty) _inverse->invert(getMatrix()); _inverseDirty = false; }
+
+        Type                    _type;
+        
+        mutable bool            _matrixDirty;
+        mutable ref_ptr<Matrix> _matrix;
+
+        mutable bool            _inverseDirty;
+        mutable ref_ptr<Matrix> _inverse;
+        
 };
 
 };

src/osg/Transform.cpp

@@ -5,15 +5,25 @@ using namespace osg;
 Transform::Transform()
 {
     _type = DYNAMIC;
+    
     _matrix = new Matrix;
     _matrix->makeIdentity();
+    _matrixDirty = false;
+    
+    _inverse = new Matrix;
+    _inverse->makeIdentity();
+    _inverseDirty = false;
 }
 
 
 Transform::Transform(const Matrix& mat )
 {
     _type = DYNAMIC;
+
     _matrix = new Matrix(mat);
+    _matrixDirty = false;
+
+    _inverseDirty = true; // will neeed to recompute.
 }
 
 
@@ -25,6 +35,8 @@ const bool Transform::computeBound() const
 {
     if (!Group::computeBound()) return false;
 
+    if (_matrixDirty) computeMatrix();
+
     Vec3 xdash = _bsphere._center;
     xdash.x() += _bsphere._radius;
     xdash = xdash*(*_matrix);