Because some unfortunate code in the Windows platform plugin generates expose events even when the size has not changed. This is of course wrong. It will be corrected by https://codereview.qt-project.org/#/c/103932
Cheers, Laszlo ________________________________ From: development-bounces+laszlo.agocs=theqtcompany....@qt-project.org <development-bounces+laszlo.agocs=theqtcompany....@qt-project.org> on behalf of Trent Reed <treed0...@gmail.com> Sent: Sunday, January 18, 2015 6:04 AM To: development@qt-project.org Subject: [Development] Under Windows QWindow receiving QExposeEvent on window drag. I am attempting to animate a QOpenGLWindow, so I'm connecting SIGNAL(frameSwapped()) with SLOT(update()) to force update on vsync as recommended in the documentation. So far so good, under *nix OSes this works fine. (Tested on x64 Ubuntu and OS X) But on Windows, when dragging a window around, the QExposeEvent gets sent out while dragging the window, causing the window to lag noticeably. (This does NOT happen on *nix OSes!) I am able to "hack" a fix by caching the previous QRegion in my derived QOpenGLWindow class, and checking to see if the new exposeEvent->region() is the same as the cached QRegion. If the cached region is the same, I ignore the event. If they are different, I pass it down to QOpenGLWindow. This appears to fix the problem. Here is my change that fixes the problem under my own project: https://github.com/TReed0803/QtOpenGL/commit/f243e879b1d639fd838deffd6b2ca095062addc1 I feel I shouldn't have to do this, it seems kind of hacky. Is this a bug? Thanks, - Trent Reed
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