Important: Please read the Qt Code of Conduct -

The performance of QPainter::drawImage

  • Dear all,

    Currently Im porting an application written with QT 4.8 on windows into mac os x. I found the performance of QPainter::drawImage differs dramatically on mac os x and windows.

    After I googled a bunch of articles and profile my qt application on mac, I found the reason is that the mac version drawImage was implemented by calling Quartz function CGContextDrawImage which consequently calls argb32_sample_argb32. argb32_sample_argb32 wastes most of the cpu cycles.

    Most probably, mac os x convert generic color space into device-dependent color space in the API CGContextDrawImage. However I modified the source code of QT 4.8 the obtain the system display color space directly.

    The result is still not good. My mac version app is significantly slower than windows version.

    Anyone can tell me why?

    /// QT 4.8's source code modified by me

    CGColorSpaceRef QCoreGraphicsPaintEngine::macGenericColorSpace()

    #if 0
    if (!m_genericColorSpace) {
    if (QSysInfo::MacintoshVersion >= QSysInfo::MV_10_4) {
    m_genericColorSpace = CGColorSpaceCreateWithName(kCGColorSpaceGenericRGB);
    } else
    m_genericColorSpace = CGColorSpaceCreateDeviceRGB();
    if (!m_postRoutineRegistered) {
    m_postRoutineRegistered = true;
    return m_genericColorSpace;
    // Just return the main display colorspace for the moment.
    // return macDisplayColorSpace();
    return CreateSystemColorSpace();

    CGColorSpaceRef CreateSystemColorSpace () {
    CMProfileRef sysprof = NULL;
    CGColorSpaceRef dispColorSpace = NULL;

    // Get the Systems Profile for the main display
    if (CMGetSystemProfile(&sysprof) == noErr)
    // Create a colorspace with the systems profile
    dispColorSpace = CGColorSpaceCreateWithPlatformColorSpace(sysprof);

      // Close the profile                                                                                                                                                                                                                                                      

    return dispColorSpace;

    [EDIT: code formatting, please wrap in @-tags, Volker]

  • Welcome to devnet

    You need to embrace your code section with '@' "(See also)":
    Otherwise it is unreadable. You can edit your post with the link below your name.

  • Did you ever get to the bottom of this?

Log in to reply