QPixmapCache

The QPixmapCache class provides an application-wide cache for pixmaps. More

Inheritance diagram of PySide2.QtGui.QPixmapCache

Synopsis

Functions

Static functions

Detailed Description

This class is a tool for optimized drawing with QPixmap . You can use it to store temporary pixmaps that are expensive to generate without using more storage space than cacheLimit() . Use insert() to insert pixmaps, find() to find them, and clear() to empty the cache.

QPixmapCache contains no member data, only static functions to access the global pixmap cache. It creates an internal QCache object for caching the pixmaps.

The cache associates a pixmap with a user-provided string as a key, or with a Key that the cache generates. Using Key for keys is faster than using strings. The string API is very convenient for complex keys but the Key API will be very efficient and convenient for a one-to-one object-to-pixmap mapping - in this case, you can store the keys as members of an object.

If two pixmaps are inserted into the cache using equal keys then the last pixmap will replace the first pixmap in the cache. This follows the behavior of the QHash and QCache classes.

The cache becomes full when the total size of all pixmaps in the cache exceeds cacheLimit() . The initial cache limit is 10240 KB (10 MB); you can change this by calling setCacheLimit() with the required value. A pixmap takes roughly (width * height * depth )/8 bytes of memory.

The Qt Quarterly article Optimizing with QPixmapCache explains how to use QPixmapCache to speed up applications by caching the results of painting.

Note

QPixmapCache is only usable from the application’s main thread. Access from other threads will be ignored and return failure.

See also

QCache QPixmap

class QPixmapCache
static PySide2.QtGui.QPixmapCache.cacheLimit()
Return type

int

Returns the cache limit (in kilobytes).

The default cache limit is 10240 KB.

See also

setCacheLimit()

static PySide2.QtGui.QPixmapCache.clear()

Removes all pixmaps from the cache.

PySide2.QtGui.QPixmapCache.find(arg__1)
Parameters

arg__1Key

static PySide2.QtGui.QPixmapCache.find(key, pixmap)
Parameters
Return type

bool

static PySide2.QtGui.QPixmapCache.find(key)
Parameters

key – unicode

Return type

QPixmap

Note

This function is deprecated.

This is an overloaded function.

Use bool find(const QString &, QPixmap *) instead.

Returns the pixmap associated with the key in the cache, or null if there is no such pixmap.

Warning

If valid, you should copy the pixmap immediately (this is fast). Subsequent insertions into the cache could cause the pointer to become invalid. For this reason, we recommend you use bool find(const QString &, QPixmap *) instead.

Example:

pm = QPixmap()
if not QPixmapCache.find("my_big_image", pm):
    pm.load("bigimage.png")
    QPixmapCache.insert("my_big_image", pm)
painter.drawPixmap(0, 0, pm)
static PySide2.QtGui.QPixmapCache.find(key, pixmap)
Parameters
  • key – unicode

  • pixmapQPixmap

Return type

bool

Note

This function is deprecated.

static PySide2.QtGui.QPixmapCache.find(key, pixmap)
Parameters
  • key – unicode

  • pixmapQPixmap

Return type

bool

static PySide2.QtGui.QPixmapCache.insert(pixmap)
Parameters

pixmapQPixmap

Return type

Key

Inserts a copy of the given pixmap into the cache and returns a key that can be used to retrieve it.

When a pixmap is inserted and the cache is about to exceed its limit, it removes pixmaps until there is enough room for the pixmap to be inserted.

The oldest pixmaps (least recently accessed in the cache) are deleted when more space is needed.

static PySide2.QtGui.QPixmapCache.insert(key, pixmap)
Parameters
  • key – unicode

  • pixmapQPixmap

Return type

bool

Inserts a copy of the pixmap pixmap associated with the key into the cache.

All pixmaps inserted by the Qt library have a key starting with “$qt”, so your own pixmap keys should never begin “$qt”.

When a pixmap is inserted and the cache is about to exceed its limit, it removes pixmaps until there is enough room for the pixmap to be inserted.

The oldest pixmaps (least recently accessed in the cache) are deleted when more space is needed.

The function returns true if the object was inserted into the cache; otherwise it returns false .

See also

setCacheLimit()

static PySide2.QtGui.QPixmapCache.remove(key)
Parameters

keyKey

static PySide2.QtGui.QPixmapCache.remove(key)
Parameters

key – unicode

static PySide2.QtGui.QPixmapCache.replace(key, pixmap)
Parameters
Return type

bool

Replaces the pixmap associated with the given key with the pixmap specified. Returns true if the pixmap has been correctly inserted into the cache; otherwise returns false .

static PySide2.QtGui.QPixmapCache.setCacheLimit(arg__1)
Parameters

arg__1int

Sets the cache limit to n kilobytes.

The default setting is 10240 KB.

See also

cacheLimit()