QPixmapCache¶
Synopsis¶
Detailed Description¶
The PySide.QtGui.QPixmapCache class provides an application-wide cache for pixmaps.
This class is a tool for optimized drawing with PySide.QtGui.QPixmap . You can use it to store temporary pixmaps that are expensive to generate without using more storage space than PySide.QtGui.QPixmapCache.cacheLimit() . Use PySide.QtGui.QPixmapCache.insert() to insert pixmaps, PySide.QtGui.QPixmapCache.find() to find them, and PySide.QtGui.QPixmapCache.clear() to empty the cache.
PySide.QtGui.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 QPixmapCache.Key that the cache generates. Using QPixmapCache.Key for keys is faster than using strings. The string API is very convenient for complex keys but the QPixmapCache.Key API will be very efficient and convenient for a one-to-one object-to-pixmap mapping .. raw:: html — 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 PySide.QtGui.QPixmapCache.cacheLimit() . The initial cache limit is 2048 KB (2 MB) on embedded platforms, 10240 KB (10 MB) on desktop platforms; you can change this by calling PySide.QtGui.QPixmapCache.setCacheLimit() with the required value. A pixmap takes roughly (width * height * depth )/8 bytes of memory.
The Qt Quarterly article Optimizing with PySide.QtGui.QPixmapCache explains how to use PySide.QtGui.QPixmapCache to speed up applications by caching the results of painting.
See also
QCache PySide.QtGui.QPixmap
- class PySide.QtGui.QPixmapCache¶
- static PySide.QtGui.QPixmapCache.cacheLimit()¶
Return type: PySide.QtCore.int Returns the cache limit (in kilobytes).
The default cache limit is 2048 KB on embedded platforms, 10240 KB on desktop platforms.
- static PySide.QtGui.QPixmapCache.clear()¶
Removes all pixmaps from the cache.
- static PySide.QtGui.QPixmapCache.find(key)¶
Parameters: key – unicode Return type: PySide.QtGui.QPixmap This is an overloaded function.
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 PySide.QtCore.QString &, PySide.QtGui.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 PySide.QtGui.QPixmapCache.find(key, pixmap)
Parameters: - key – unicode
- pixmap – PySide.QtGui.QPixmap
Return type: PySide.QtCore.bool
Looks for a cached pixmap associated with the given key in the cache. If the pixmap is found, the function sets pixmap to that pixmap and returns true; otherwise it leaves pixmap alone and returns false.
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 PySide.QtGui.QPixmapCache.find(key, pixmap)
Parameters: - key – PySide.QtGui.QPixmapCache::Key
- pixmap – PySide.QtGui.QPixmap
Return type: PySide.QtCore.bool
Looks for a cached pixmap associated with the given key in the cache. If the pixmap is found, the function sets pixmap to that pixmap and returns true; otherwise it leaves pixmap alone and returns false. If the pixmap is not found, it means that the key is no longer valid, so it will be released for the next insertion.
- PySide.QtGui.QPixmapCache.find(arg__1)
Parameters: arg__1 – PySide.QtGui.QPixmapCache::Key
- static PySide.QtGui.QPixmapCache.insert(key, pixmap)¶
Parameters: - key – unicode
- pixmap – PySide.QtGui.QPixmap
Return type: PySide.QtCore.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.
- static PySide.QtGui.QPixmapCache.insert(pixmap)
Parameters: pixmap – PySide.QtGui.QPixmap Return type: PySide.QtGui.QPixmapCache::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 PySide.QtGui.QPixmapCache.remove(key)¶
Parameters: key – unicode Removes the pixmap associated with key from the cache.
- static PySide.QtGui.QPixmapCache.remove(key)
Parameters: key – PySide.QtGui.QPixmapCache::Key Removes the pixmap associated with key from the cache and releases the key for a future insertion.
- static PySide.QtGui.QPixmapCache.replace(key, pixmap)¶
Parameters: - key – PySide.QtGui.QPixmapCache::Key
- pixmap – PySide.QtGui.QPixmap
Return type: PySide.QtCore.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 PySide.QtGui.QPixmapCache.setCacheLimit(arg__1)¶
Parameters: arg__1 – PySide.QtCore.int Sets the cache limit to n kilobytes.
The default setting is 2048 KB on embedded platforms, 10240 KB on desktop platforms.
