Source: kpixmapio.h


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/* vi: ts=8 sts=4 sw=4
 *
 * $Id: kpixmapio_h.html 132191 2002-01-17 21:32:13Z dfaure $
 *
 * This file is part of the KDE project, module kdeui.
 * Copyright (C) 2000 Geert Jansen 
 * 
 * You can Freely distribute this program under the GNU Library General 
 * Public License. See the file "COPYING.LIB" for the exact licensing terms.
 */

#ifndef __KPixmapIO_h_Included__
#define __KPixmapIO_h_Included__

class QPixmap;
class QImage;
class KPixmapIOData;

/**
 * @short Fast QImage to/from QPixmap conversion.
 * @author Geert Jansen 
 * @version $Id: kpixmapio_h.html 132191 2002-01-17 21:32:13Z dfaure $
 *
 * KPixmapIO implements a fast path for QPixmap to/from QImage conversions.
 * It uses the MIT-SHM shared memory extension for this. If this extension is 
 * not available, it will fall back to standard Qt methods. 
 *
 * @sect Typical usage
 *
 * You can use KPixmapIO for load/saving pixmaps.
 *
 * 
 * KPixmapIO io;
 * pixmap = io.convertToPixmap(image);
 * image = io.convertToImage(pixmap);
 * 
* * It also has functionality for partially updating/saving pixmaps, see * @ref #putImage and @ref #getImage. * * @sect KPixmapIO vs. Qt speed comparison * * Speed measurements were taken. These show that usage of KPixmapIO for * images up to a certain threshold size, offers no speed advantage over * the Qt routines. Below you can see a plot of these measurements. * * @image kpixmapio-perf.png Ignored_But_Necessary_Word_For_Kdoc * * The threshold size, amongst other causes, is determined by the shared * memory allocation policy. If the policy is @p ShmDontKeep, the * shared memory segment is discarded right after usage, and thus needs to * be allocated before each transfer. This introduces a a setup penalty not * present when the policy is @p ShmKeepAndGrow. In this case the * shared memory segment is kept and resized when necessary, until the * KPixmapIO object is destroyed. * * The default policy is @p ShmDontKeep. This policy makes sense when * loading pixmaps once. The corresponding threshold is taken at 5.000 * pixels as suggested by experiments. Below this threshold, KPixmapIO * will not use shared memory and fall back on the Qt routines. * * When the policy is @p ShmKeepAndGrow, the threshold is taken at * 2.000 pixels. Using this policy, you might want to use @ref #preAllocShm * to pre-allocate a certain amount of shared memory, in order to avoid * resizes. This allocation policy makes sense in a multimedia type * application where you are constantly updating the screen. * * Above a couple times the threshold size, KPixmapIO's and Qt's speed become * linear in the number of pixels, KPixmapIO being at least 2, and mostly around * 4 times faster than Qt, depending on the screen and image depth. * * Speed difference seems to be the most at 16 bpp, followed by 32 and 24 * bpp respectively. This can be explained by the relatively poor * implementation of 16 bit RGB packing in Qt, while at 32 bpp we need to * transfer more data, and thus gain more, than at 24 bpp. * * @sect Conclusion * * For large pixmaps, there's a definite speed improvement when using * KPixmapIO. On the other hand, there's no speed improvement for small * pixmaps. When you know you're only transferring small pixmaps, there's no * point in using it. */ class KPixmapIO { public: KPixmapIO(); ~KPixmapIO(); /** * Convert an image to a pixmap. * @param image The image to convert. * @return The pixmap containing the image. */ QPixmap convertToPixmap(const QImage &image); /** * Convert a pixmap to an image. * @param pixmap The pixmap to convert. * @return The image. */ QImage convertToImage(const QPixmap &pixmap); /** * Bitblt an image onto a pixmap. * @param dst The destination pixmap. * @param dx Destination x offset. * @param dy Destination y offset. * @param src The image to load. */ void putImage(QPixmap *dst, int dx, int dy, const QImage *src); /** * This function is identical to the one above. It only differs in the * arguments it accepts. */ void putImage(QPixmap *dst, const QPoint &offset, const QImage *src); /** * Transfer (a part of) a pixmap to an image. * @param src The source pixmap. * @param sx Source x offset. * @param sy Source y offset. * @param sw Source width. * @param sh Source height. * @return The image. */ QImage getImage(const QPixmap *src, int sx, int sy, int sw, int sh); /** * This function is identical to the one above. It only differs in the * arguments it accepts. */ QImage getImage(const QPixmap *src, const QRect &rect); /** * Shared memory allocation policies. */ enum ShmPolicies { ShmDontKeep, ShmKeepAndGrow }; /** * Set the shared memory allocation policy. See the introduction for * KPixmapIO for a discussion. * @param policy The alloction policy. */ void setShmPolicy(int policy); /** * Pre-allocate shared memory. KPixmapIO will be able to transfer images * up to this size without resizing. * @param size The size of the image in @p pixels. */ void preAllocShm(int size); private: /* * Supported XImage byte orders. The notation ARGB means bytes * containing A:R:G:B succeed in memory. */ enum ByteOrders { bo32_ARGB, bo32_BGRA, bo24_RGB, bo24_BGR, bo16_RGB_565, bo16_BGR_565, bo16_RGB_555, bo16_BGR_555, bo8 }; bool m_bShm; class KPixmapIOData *d; void initXImage(int w, int h); void doneXImage(); void createXImage(int w, int h); void destroyXImage(); void createShmSegment(int size); void destroyShmSegment(); void convertToXImage(const QImage &); QImage convertFromXImage(); }; #endif // __KPixmapIO_h_Included__

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