KPixmapCache

#include <kpixmapcache.h>

Public Types

enum  RemoveStrategy { RemoveOldest, RemoveSeldomUsed, RemoveLeastRecentlyUsed }
 

Public Member Functions

 KPixmapCache (const QString &name)
 
int cacheLimit () const
 
void discard ()
 
virtual bool find (const QString &key, QPixmap &pix)
 
virtual void insert (const QString &key, const QPixmap &pix)
 
bool isEnabled () const
 
bool isValid () const
 
QPixmap loadFromFile (const QString &filename)
 
QPixmap loadFromSvg (const QString &filename, const QSize &size=QSize())
 
void removeEntries (int newsize=0)
 
RemoveStrategy removeEntryStrategy () const
 
void setCacheLimit (int kbytes)
 
void setRemoveEntryStrategy (RemoveStrategy strategy)
 
void setTimestamp (const QDateTime &time)
 
void setUseQPixmapCache (bool use)
 
int size () const
 
QDateTime timestamp () const
 
bool useQPixmapCache () const
 

Static Public Member Functions

static void deleteCache (const QString &name)
 

Protected Member Functions

void ensureInited () const
 
virtual bool loadCustomData (QDataStream &stream)
 
virtual bool loadCustomIndexHeader (QDataStream &stream)
 
bool recreateCacheFiles ()
 
void setValid (bool valid)
 
virtual bool writeCustomData (QDataStream &stream)
 
virtual void writeCustomIndexHeader (QDataStream &stream)
 

Detailed Description

General-purpose pixmap cache for KDE.

The pixmap cache can be used to store pixmaps which can later be loaded from the cache very quickly.

Its most common use is storing SVG images which might be expensive to render every time they are used. With the cache you can render each SVG only once and later use the stored version unless the SVG file or requested pixmap size changes.

KPixmapCache's API is similar to that of the QPixmapCache so if you're already using the latter then all you need to do is creating a KPixmapCache object (unlike QPixmapCache, KPixmapCache doesn't have many static methods) and calling insert() and find() method on that object:

// Create KPixmapCache object
KPixmapCache* cache = new KPixmapCache("myapp-pixmaps");
// Load a pixmap
QPixmap pix;
if (!cache->find("pixmap-1", pix)) {
// Pixmap isn't in the cache, create it and insert to cache
pix = createPixmapFromData();
cache->insert("pixmap-1", pix);
}
// Use pix

The above example illustrates that you can also cache pixmaps created from some data. In case such data is updated, you might need to discard cache contents using discard() method:

// Discard the cache if it's too old
if (cache->timestamp() < mydataTimestamp()) {
cache->discard();
}
// Now the cache contains up-to-date data

As demonstrated, you can use cache's timestamp() method to see when the cache was created. If necessary, you can also change the timestamp using setTimestamp() method.

Deprecated:
KPixmapCache is susceptible to various non-trivial locking bugs and inefficiencies, and is supported for backward compatibility only (since it exposes a QDataStream API for subclasses). Users should port to KImageCache for a very close work-alike, or KSharedDataCache if they need more control.
See also
KImageCache, KSharedDataCache
Author
Rivo Laks

Definition at line 85 of file kpixmapcache.h.

Member Enumeration Documentation

Describes which entries will be removed first during cache cleanup.

See also
removeEntryStrategy(),
setRemoveEntryStrategy()
Enumerator
RemoveOldest 

oldest entries are removed first.

RemoveSeldomUsed 

least used entries are removed first.

RemoveLeastRecentlyUsed 

least recently used entries are removed first.

Definition at line 216 of file kpixmapcache.h.

Constructor & Destructor Documentation

KPixmapCache::KPixmapCache ( const QString name)
explicit

Constucts the pixmap cache object.

Parameters
nameunique name of the cache

Definition at line 964 of file kpixmapcache.cpp.

Member Function Documentation

int KPixmapCache::cacheLimit ( ) const
Returns
maximum size of the cache (in kilobytes). Default setting is 3 megabytes (1 megabyte = 2^20 bytes).

Definition at line 1103 of file kpixmapcache.cpp.

void KPixmapCache::deleteCache ( const QString name)
static

Deletes a pixmap cache.

Parameters
nameunique name of the cache to be deleted

Definition at line 1197 of file kpixmapcache.cpp.

void KPixmapCache::discard ( )

Deletes all entries and reinitializes this cache.

NOTE: If useQPixmapCache is set to true then that cache must also be cleared. There is only one QPixmapCache for the entire process however so other KPixmapCaches and other QPixmapCache users may also be affected, leading to a temporary slowdown until the QPixmapCache is repopulated.

Definition at line 1207 of file kpixmapcache.cpp.

void KPixmapCache::ensureInited ( ) const
protected

Makes sure that the cache is initialized correctly, including the loading of the cache index and data, and any shared memory attachments (for systems where that is enabled).

Note
Although this method is protected you should not use it from any subclasses.

Definition at line 1013 of file kpixmapcache.cpp.

bool KPixmapCache::find ( const QString key,
QPixmap pix 
)
virtual

Tries to load pixmap with the specified key from cache.

If the pixmap is found it is stored in pix, otherwise pix is unchanged.

Returns
true when pixmap was found and loaded from cache, false otherwise

Definition at line 1253 of file kpixmapcache.cpp.

void KPixmapCache::insert ( const QString key,
const QPixmap pix 
)
virtual

Inserts the pixmap pix into the cache, associated with the key key.

Any existing pixmaps associated with key are overwritten.

Definition at line 1347 of file kpixmapcache.cpp.

bool KPixmapCache::isEnabled ( ) const

Cache will be disabled when e.g.

its data file cannot be created or read.

Returns
true when the cache is enabled.

Definition at line 1029 of file kpixmapcache.cpp.

bool KPixmapCache::isValid ( ) const
Returns
true when the cache is ready to be used. Not being valid usually means that some additional initialization has to be done before the cache can be used.

Definition at line 1035 of file kpixmapcache.cpp.

bool KPixmapCache::loadCustomData ( QDataStream stream)
protectedvirtual

Can be used by subclasses to load custom data from the stream.

This function will be called by KPixmapCache immediately following the image data for a single image being read from stream. (This function is called once for every single image).

See also
writeCustomData
loadCustomIndexHeader
Parameters
streamthe QDataStream to read data from
Returns
true if custom data was successfully loaded, false otherwise. If false is returned then the cached item is assumed to be invalid and will not be available to find() or contains().

Definition at line 1342 of file kpixmapcache.cpp.

bool KPixmapCache::loadCustomIndexHeader ( QDataStream stream)
protectedvirtual

Can be used by subclasses to load custom data from cache's header.

This function will be called by KPixmapCache immediately after the index header has been written out. (This function is called one time only for the entire cache).

See also
loadCustomData
writeCustomIndexHeader
Parameters
streamthe QDataStream to read data from
Returns
true if custom index header data was successfully read, false otherwise. If false is returned then the cache is assumed to be invalid and further processing does not occur.

Definition at line 1020 of file kpixmapcache.cpp.

QPixmap KPixmapCache::loadFromFile ( const QString filename)

Loads a pixmap from given file, using the cache.

If the file does not exist on disk, an empty pixmap is returned, even if that file had previously been cached. In addition, if the file's modified-time is more recent than cache's timestamp(), the entire cache is discarded (to be regenerated). This behavior may change in a future KDE Platform release. If the cached data is current the pixmap is returned directly from the cache without any file loading.

Note
The mapping between filename and the actual key used internally is implementation-dependent and can change without warning. Use insert() manually if you need control of the key, otherwise consistently use this function.
Parameters
filenameThe name of the pixmap to load, cache, and return.
Returns
The given pixmap, or an empty pixmap if the file was invalid or did not exist.

Definition at line 1428 of file kpixmapcache.cpp.

QPixmap KPixmapCache::loadFromSvg ( const QString filename,
const QSize size = QSize() 
)

Same as loadFromFile(), but using an SVG file instead.

You may optionally pass in a size to control the size of the output pixmap.

Note
The returned pixmap is only cached for identical filenames and sizes. If you change the size in between calls to this function then the pixmap will have to be regenerated again.
Parameters
filenameThe filename of the SVG file to load.
sizesize of the pixmap where the SVG is render to. If not given then the SVG file's default size is used.
Returns
an empty pixmap if the file does not exist or was invalid, otherwise a pixmap of the desired size.

Definition at line 1454 of file kpixmapcache.cpp.

bool KPixmapCache::recreateCacheFiles ( )
protected

This function causes the cache files to be recreate by invalidating the cache.

Any shared memory mappings (if enabled) are dropped temporarily as well.

Note
The recreated cache will be initially empty, but with the same size limits and entry removal strategy (see removeEntryStrategy()).

If you use this in a subclass be prepared to handle writeCustomData() and writeCustomIndexHeader().

Returns
true if the cache was successfully recreated.

Definition at line 1137 of file kpixmapcache.cpp.

void KPixmapCache::removeEntries ( int  newsize = 0)

Removes some of the entries in the cache according to current removeEntryStrategy().

Parameters
newsizewanted size of the cache, in bytes. If 0 is given then current cacheLimit() is used.
Warning
This currently works by copying some entries to a new cache and then replacing the old cache with the new one. Thus it might be slow and will temporarily use extra disk space.

Definition at line 1239 of file kpixmapcache.cpp.

KPixmapCache::RemoveStrategy KPixmapCache::removeEntryStrategy ( ) const
Returns
current entry removal strategy. Default is RemoveLeastRecentlyUsed.

Definition at line 1127 of file kpixmapcache.cpp.

void KPixmapCache::setCacheLimit ( int  kbytes)

Sets the maximum size of the cache (in kilobytes).

If cache gets bigger than the limit then some entries are removed (according to removeEntryStrategy()).

Setting the cache limit to 0 disables caching (as all entries will get immediately removed).

Note that the cleanup might not be done immediately, so the cache might temporarily (for a few seconds) grow bigger than the limit.

Definition at line 1108 of file kpixmapcache.cpp.

void KPixmapCache::setRemoveEntryStrategy ( KPixmapCache::RemoveStrategy  strategy)

Sets the removeEntryStrategy used when removing entries.

Definition at line 1132 of file kpixmapcache.cpp.

void KPixmapCache::setTimestamp ( const QDateTime time)

Sets the timestamp of app-specific cache.

It's saved in the cache file and can later be retrieved using the timestamp() method. By default the timestamp is set to the cache creation time.

Definition at line 1053 of file kpixmapcache.cpp.

void KPixmapCache::setUseQPixmapCache ( bool  use)

Sets whether QPixmapCache (memory caching) should be used in addition to disk cache.

QPixmapCache is used by default.

Note
On most systems KPixmapCache can use shared-memory to share cached pixmaps with other applications attached to the same shared pixmap, which means additional memory caching is unnecessary and actually wasteful of memory.
Warning
QPixmapCache is shared among the entire process and therefore can cause strange interactions with other instances of KPixmapCache. This may be fixed in the future and should be not relied upon.

Definition at line 1093 of file kpixmapcache.cpp.

void KPixmapCache::setValid ( bool  valid)
protected

Sets whether this cache is valid or not.

(The cache must be enabled in addition for isValid() to return true.

See also
isEnabled(),
setEnabled()).

Most cache functions do not work if the cache is not valid. KPixmapCache assumes the cache is valid as long as its cache files were able to be created (see recreateCacheFiles()) even if the cache is not enabled.

Can be used by subclasses to indicate that cache needs some additional initialization before it can be used (note that KPixmapCache will not handle actually performing this extra initialization).

Definition at line 1041 of file kpixmapcache.cpp.

int KPixmapCache::size ( ) const
Returns
approximate size of the cache, in kilobytes (1 kilobyte == 1024 bytes)

Definition at line 1084 of file kpixmapcache.cpp.

QDateTime KPixmapCache::timestamp ( ) const
Note
KPixmapCache does not ever change the timestamp, so the application must set the timestamp if it to be used.
Returns
Timestamp of the cache, set using the setTimestamp() method.

Definition at line 1047 of file kpixmapcache.cpp.

bool KPixmapCache::useQPixmapCache ( ) const

Whether QPixmapCache should be used to cache pixmaps in memory in addition to caching them on the disk.

NOTE: The design of QPixmapCache means that the entries stored in the cache are shared throughout the entire process, and not just in this particular KPixmapCache. KPixmapCache makes an effort to ensure that entries from other KPixmapCaches do not inadvertently spill over into this one, but is not entirely successful (see discard())

Definition at line 1098 of file kpixmapcache.cpp.

bool KPixmapCache::writeCustomData ( QDataStream stream)
protectedvirtual

Can be used by subclasses to write custom data into the stream.

This function will be called by KPixmapCache immediately after the image data for a single image has been written to stream. (This function is called once for every single image).

See also
loadCustomData
writeCustomIndexHeader
Parameters
streamthe QDataStream to write data to

Definition at line 1410 of file kpixmapcache.cpp.

void KPixmapCache::writeCustomIndexHeader ( QDataStream stream)
protectedvirtual

Can be used by subclasses to write custom data into cache's header.

This function will be called by KPixmapCache immediately following the index header has being loaded. (This function is called one time only for the entire cache).

See also
writeCustomData
loadCustomIndexHeader
Parameters
streamthe QDataStream to write data to

Definition at line 1025 of file kpixmapcache.cpp.


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