Slow Graphics since Qt 5.6.0

[mireiner]

Hi there,

the problem:
The graphic animations of the same Qt application are running on Qt 5.4.2, Qt 5.5.0 and Qt 5.5.1 just fine. But on Qt 5.6.0, Qt 5.6.1 and Qt 5.7.0 at minimum 100% slower. No matter if MinGW 32 bit or Microsoft 32 or 64 bit compiler is used.

Setup:
Processor: Intel Core 2 Duo E8400 @ 3.00GHz
RAM: 8GB
Graphicscard: ATI Radeon HD 3600 - Directx 10.1 (non gamer card)
Operating System: Windows 10 64 bit (no enviroment variable set for Qt)
IDE: Qt Creator
Qt Windows Desktop Application 32 and 64bit.
Graphic Animations run on QWidget with QPainter and 100x drawText() and 400x drawLine() functions.
Animations are started with mouse click and hold on QPushbutton with autorepeat=true and "autorepeatinterval"=0

I tried to isolate the problem to a specific part of the application without success. If QPainter::drawText() is disabled in the full application, then it seams the speed is there again. But if I program a small test application with massiv use of QPainter::drawText() only, there is no slow down between the different Qt versions.

It's hard for me to understand on what graphics driver my Qt application is running on Windows 10 (ANGLE or OpenGL?). So eventually there might be the problem. Because I did not change anything in my Qt application when testing the obove mentioned Qt versions. Should I have done that? For example set an Windows enviroment variable oder an entry in project file (*.pro)?

Does anybody know what the problem might be, or provide tips how to find the issue?