NAME

       SoCache -

       The SoCache class is the superclass for all internal cache classes.

       It organizes reference counting to make it possible to share cache instances. It also
       organizes a list of elements that will affect the cache. If any of the elements have
       changed since the cache was created, the cache is invalid.

SYNOPSIS

       #include <Inventor/caches/SoCache.h>

       Inherited by SoBoundingBoxCache, SoConvexDataCache, SoGLRenderCache, SoNormalCache,
       SoPrimitiveVertexCache, and SoTextureCoordinateCache.

   Public Member Functions
       SoCache (SoState *const state)
       void ref (void)
       void unref (SoState *state=NULL)
       void addElement (const SoElement *const elem)
       virtual void addCacheDependency (const SoState *state, SoCache *cache)
       virtual SbBool isValid (const SoState *state) const
       const SoElement * getInvalidElement (const SoState *const state) const
       void invalidate (void)

   Protected Member Functions
       virtual void destroy (SoState *state)
       virtual ~SoCache ()

Detailed Description

       The SoCache class is the superclass for all internal cache classes.

       It organizes reference counting to make it possible to share cache instances. It also
       organizes a list of elements that will affect the cache. If any of the elements have
       changed since the cache was created, the cache is invalid.

       The cache element test algorithm in Coin works like this:

       Every element that is read before it's written when a cache is created is stored in the
       SoCache's element list. This is done to detect when something outside the cache changes.

       Example: you have a SoCoordinate3 node outside an SoSeparator, but an SoIndexedFaceSet
       inside the SoSeparator. If the SoSeparator creates a cache, SoIndexedFaceSet will read
       SoCoordinateElement, and since SoCoordinateElement hasn't been set after the cache was
       opened, the cache stores that element in the cache's list of element dependencies.

       At the next frame, the SoSeparator will test if the cache is valid, and will then test all
       dependency elements. If one of the elements doesn't match, the cache is not valid and
       can't be used.

       That's the basics. There are some steps you have to do when creating a cache to make the
       cache dependencies work. Basically you have to do it like this:

       SbBool storedinvalid = SoCacheElement::setInvalid(FALSE);
       state->push();
       SoMyCache * cache = new SoMyCache(state);
       cache->ref();
       SoCacheElement::set(state, cache);
       buildMyCache();
       state->pop();
       SoCacheElement::setInvalid(storedinvalid);

       First you reset and store the old value of the cache invalid-flag. Then you push the state
       so that the cache can detect when something outside the cache is changed (and to be able
       to change the cache element). Next, you create the cache - don't forget to ref it.
       Finally, set the current cache in the cache element and build the cache. After building
       the cache, you pop the state and restore the invalid-cache flag.

       When building the cache, all elements that are read will be copied into the cache (using
       SoElement::copyMatchInfo()), and these copied elements are used to test the validity of
       the cache (in SoCache::isValid()).

       You don't have to manually add element dependencies. They will automatically be picked up
       when creating the cache. This is handled in SoElement::getConstElement().

       If you want the cache to be invalidated when some field inside your node is changed, it's
       common to overload the notify()-method, and call SoCache::invalidate() whenever the
       notify()-method for your node is called. See for instance SoShape::notify().

       Also, don't delete the cache in your notify() method. Wait until the next time the cache
       is needed before unref-ing the old cache.

Constructor & Destructor Documentation

   SoCache::SoCache (SoState *conststate)
       Constructor with state being the current state.

   SoCache::~SoCache () [protected],  [virtual]
       Destructor

Member Function Documentation

   void SoCache::ref (void)
       Increases the reference count by one.

   void SoCache::unref (SoState *state = NULL)
       Decreases the reference count by one. When the reference count reaches zero, the cache is
       deleted. The SoCache::destroy() method is called before the destructor is called.

   void SoCache::addElement (const SoElement *constelem)
       Adds elem to the list of elements this cache depends on.

   void SoCache::addCacheDependency (const SoState *state, SoCache *cache) [virtual]
       Adds dependencies from cache to this cache.

   SbBool SoCache::isValid (const SoState *state) const [virtual]
       Return TRUE if this cache is valid, FALSE otherwise.

       Reimplemented in SoPrimitiveVertexCache, and SoGLRenderCache.

   const SoElement * SoCache::getInvalidElement (const SoState *conststate) const
       Returns the element that caused the invalidation. Returns NULL if the cache is valid, or
       if the cache was not invalidated bacause of an element.

   void SoCache::invalidate (void)
       Forces a cache to be invalid.

   void SoCache::destroy (SoState *state) [protected],  [virtual]
       Can be overridden by subclasses to clean up before they are deleted. Default method does
       nothing.

       Reimplemented in SoGLRenderCache.

Author

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