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

◆ RemoveStrategy

enum KPixmapCache::RemoveStrategy

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::KPixmapCache ( const QString & name )

explicit

Constucts the pixmap cache object.

Parameters

name	unique name of the cache

Definition at line 962 of file kpixmapcache.cpp.

Member Function Documentation

◆ cacheLimit()

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 1101 of file kpixmapcache.cpp.

◆ deleteCache()

void KPixmapCache::deleteCache ( const QString & name )

static

Deletes a pixmap cache.

Parameters

name	unique name of the cache to be deleted

Definition at line 1195 of file kpixmapcache.cpp.

◆ discard()

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 1205 of file kpixmapcache.cpp.

◆ ensureInited()

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 1011 of file kpixmapcache.cpp.

◆ find()

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 1251 of file kpixmapcache.cpp.

◆ insert()

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 1345 of file kpixmapcache.cpp.

◆ isEnabled()

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 1027 of file kpixmapcache.cpp.

◆ isValid()

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 1033 of file kpixmapcache.cpp.

◆ loadCustomData()

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

stream the 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 1340 of file kpixmapcache.cpp.

◆ loadCustomIndexHeader()

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

stream the 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 1018 of file kpixmapcache.cpp.

◆ loadFromFile()

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

filename The 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 1426 of file kpixmapcache.cpp.

◆ loadFromSvg()

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

filename	The filename of the SVG file to load.
size	size 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 1452 of file kpixmapcache.cpp.

◆ recreateCacheFiles()

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 1135 of file kpixmapcache.cpp.

◆ removeEntries()

void KPixmapCache::removeEntries ( int newsize = 0 )

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

Parameters

newsize wanted 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 1237 of file kpixmapcache.cpp.

◆ removeEntryStrategy()

KPixmapCache::RemoveStrategy KPixmapCache::removeEntryStrategy ( ) const

Returns: current entry removal strategy. Default is RemoveLeastRecentlyUsed.

Definition at line 1125 of file kpixmapcache.cpp.

◆ setCacheLimit()

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 1106 of file kpixmapcache.cpp.

◆ setRemoveEntryStrategy()

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

Sets the removeEntryStrategy used when removing entries.

Definition at line 1130 of file kpixmapcache.cpp.

◆ setTimestamp()

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 1051 of file kpixmapcache.cpp.

◆ setUseQPixmapCache()

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 1091 of file kpixmapcache.cpp.

◆ setValid()

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 1039 of file kpixmapcache.cpp.

◆ size()

int KPixmapCache::size ( ) const

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

Definition at line 1082 of file kpixmapcache.cpp.

◆ timestamp()

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 1045 of file kpixmapcache.cpp.

◆ useQPixmapCache()

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 1096 of file kpixmapcache.cpp.

◆ writeCustomData()

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

stream the QDataStream to write data to

Definition at line 1408 of file kpixmapcache.cpp.

◆ writeCustomIndexHeader()

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).