org.kde.koala

Class KPixmapIO

public class KPixmapIO extends Object implements QtSupport

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.
  • 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 putImage and getImage. KPixmapIO vs. Qt speed comparison\n 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. The threshold size, amongst other causes, is determined by the shared memory allocation policy. If the policy is 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 ShmKeepAndGrow. In this case the shared memory segment is kept and resized when necessary, until the KPixmapIO object is destroyed. The default policy is 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 ShmKeepAndGrow, the threshold is taken at 2.000 pixels. Using this policy, you might want to use 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.
  • 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.

    Version: $Id: KPixmapIO.java 473384 2005-10-23 14:17:09Z rdale $

    Author: Geert Jansen

    UNKNOWN: Fast QImage to/from QPixmap conversion.

    Field Summary
    static intShmDontKeep
    Shared memory allocation policies.
    static intShmKeepAndGrow
    Constructor Summary
    protected KPixmapIO(Class dummy)
    KPixmapIO()
    Method Summary
    QImageconvertToImage(QPixmap pixmap)
    Convert a pixmap to an image.
    QPixmapconvertToPixmap(QImage image)
    Convert an image to a pixmap.
    voiddispose()
    Delete the wrapped C++ instance ahead of finalize()
    protected voidfinalize()
    Deletes the wrapped C++ instance
    QImagegetImage(QPixmap src, int sx, int sy, int sw, int sh)
    Transfer (a part of) a pixmap to an image.
    QImagegetImage(QPixmap src, QRect rect)
    This function is identical to the one above.
    booleanisDisposed()
    Has the wrapped C++ instance been deleted?
    voidpreAllocShm(int size)
    Pre-allocate shared memory.
    voidputImage(QPixmap dst, int dx, int dy, QImage src)
    Bitblt an image onto a pixmap.
    voidputImage(QPixmap dst, QPoint offset, QImage src)
    This function is identical to the one above.
    voidsetShmPolicy(int policy)
    Set the shared memory allocation policy.

    Field Detail

    ShmDontKeep

    public static final int ShmDontKeep
    Shared memory allocation policies.

    UNKNOWN: Shared memory allocation policies.

    ShmKeepAndGrow

    public static final int ShmKeepAndGrow

    Constructor Detail

    KPixmapIO

    protected KPixmapIO(Class dummy)

    KPixmapIO

    public KPixmapIO()

    Method Detail

    convertToImage

    public QImage convertToImage(QPixmap pixmap)
    Convert a pixmap to an image.

    Parameters: pixmap The pixmap to convert.

    Returns: The image.

    UNKNOWN: Convert a pixmap to an image.

    convertToPixmap

    public QPixmap convertToPixmap(QImage image)
    Convert an image to a pixmap.

    Parameters: image The image to convert.

    Returns: The pixmap containing the image.

    UNKNOWN: Convert an image to a pixmap.

    dispose

    public void dispose()
    Delete the wrapped C++ instance ahead of finalize()

    finalize

    protected void finalize()
    Deletes the wrapped C++ instance

    getImage

    public QImage getImage(QPixmap src, int sx, int sy, int sw, int sh)
    Transfer (a part of) a pixmap to an image.

    Parameters: src The source pixmap. sx Source x offset. sy Source y offset. sw Source width. sh Source height.

    Returns: The image.

    UNKNOWN: Transfer (a part of) a pixmap to an image.

    getImage

    public QImage getImage(QPixmap src, QRect rect)
    This function is identical to the one above. It only differs in the arguments it accepts.

    UNKNOWN: This function is identical to the one above.

    isDisposed

    public boolean isDisposed()
    Has the wrapped C++ instance been deleted?

    preAllocShm

    public void preAllocShm(int size)
    Pre-allocate shared memory. KPixmapIO will be able to transfer images up to this size without resizing.

    Parameters: size The size of the image in pixels.

    UNKNOWN: Pre-allocate shared memory.

    putImage

    public void putImage(QPixmap dst, int dx, int dy, QImage src)
    Bitblt an image onto a pixmap.

    Parameters: dst The destination pixmap. dx Destination x offset. dy Destination y offset. src The image to load.

    UNKNOWN: Bitblt an image onto a pixmap.

    putImage

    public void putImage(QPixmap dst, QPoint offset, QImage src)
    This function is identical to the one above. It only differs in the arguments it accepts.

    UNKNOWN: This function is identical to the one above.

    setShmPolicy

    public void setShmPolicy(int policy)
    Set the shared memory allocation policy. See the introduction for KPixmapIO for a discussion.

    Parameters: policy The alloction policy.

    UNKNOWN: Set the shared memory allocation policy.