StackOverflow2013

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POThe performance of QPainter::drawImage differs dramatically on Mac OS X and Windows
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copied!<p>Currently I'm porting an application written with Qt 4.8 on Windows into Mac OS X. I found the performance of <code>QPainter::drawImage</code> differs dramatically on Mac OS X and Windows.</p> <p>After I googled a bunch of articles and profile my Qt application on Mac OS X, I found the reason is that the Mac version <code>drawImage</code> was implemented by calling Quartz function CGContextDrawImage which consequently calls <code>argb32_sample_argb32</code>. <code>argb32_sample_argb32</code> wastes most of the cpu cycles.</p> <p>Most probably, Mac OS X converts 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.</p> <p>The result is still not good. My mac version app is significantly slower than Windows version.</p> <p>Anyone can tell me why? </p> <pre><code>/// QT 4.8's source code modified by me CGColorSpaceRef QCoreGraphicsPaintEngine::macGenericColorSpace() { #if 0 if (!m_genericColorSpace) { #if MAC_OS_X_VERSION_MAX_ALLOWED >= MAC_OS_X_VERSION_10_4 if (QSysInfo::MacintoshVersion >= QSysInfo::MV_10_4) { m_genericColorSpace = CGColorSpaceCreateWithName(kCGColorSpaceGenericRGB); } else #endif { m_genericColorSpace = CGColorSpaceCreateDeviceRGB(); } if (!m_postRoutineRegistered) { m_postRoutineRegistered = true; qAddPostRoutine(QCoreGraphicsPaintEngine::cleanUpMacColorSpaces); } } return m_genericColorSpace; #else // Just return the main display colorspace for the moment. // return macDisplayColorSpace(); return CreateSystemColorSpace(); #endif } 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 CMCloseProfile(sysprof); } return dispColorSpace; } </code></pre>

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