The QPixmapCache class provides an application-wide cache for pixmaps. 更多...
The QPixmapCache class provides an application-wide cache for pixmaps.
此类是用于优化绘制的工具采用 QPixmap . You can use it to store temporary pixmaps that are expensive to generate without using more storage space than cacheLimit (). 使用 insert () to insert pixmaps, find () to find them, and clear () to empty the 缓存。
QPixmapCache contains no member data, only static functions to access the global pixmap cache. It creates an internal QCache 对象为缓存像素图。
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 — 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 类。
The cache becomes full when the total size of all pixmaps in the cache exceeds 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 setCacheLimit () with the required value. A pixmap takes roughly ( width * height * depth )/8 bytes of memory.
Qt 季刊 文章 Optimizing with QPixmapCache explains how to use QPixmapCache to speed up applications by caching the results of painting.
返回缓存限制 (以 KB 为单位)。
The default cache limit is 2048 KB on embedded platforms, 10240 KB on desktop platforms.
另请参阅 setCacheLimit ().
从缓存移除所有像素图。
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.
范例：
QPixmap pm; if (!QPixmapCache.find("my_big_image", &pm)) { pm.load("bigimage.png"); QPixmapCache.insert("my_big_image", pm); } painter->drawPixmap(0, 0, pm);
该函数在 Qt 4.6 引入。
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 If the pixmap is not found, it means that the key is no longer valid, so it will be released for the next insertion.
该函数在 Qt 4.6 引入。
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.
另请参阅 setCacheLimit ().
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.
该函数在 Qt 4.6 引入。
另请参阅 setCacheLimit () 和 replace ().
移除像素图关联 key 从 缓存。
移除像素图关联 key from the cache and releases the key for a future insertion.
该函数在 Qt 4.6 引入。
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.
该函数在 Qt 4.6 引入。
另请参阅 setCacheLimit () 和 insert ().
Sets the cache limit to n kilobytes.
The default setting is 2048 KB on embedded platforms, 10240 KB on desktop platforms.
另请参阅 cacheLimit ().
