QTestLib: Introduce initMain() to run in main before qApp exists

When running Qt autotests on a developer machine with a high
resolution, failures occur due to either some widget becoming too
small, some rounding fuzz appearing when Qt High DPI scaling is active,
or some test taking screenshots failing to deal with device pixel
ratios != 1 in the obtained pixmaps.

It is not feasible to adapt all tests to pass on high resolution
monitors in both modes (Qt High DPI scaling enabled/disabled). It
should be possible to specify the High DPI setting per test.

Previously, it was not possible to set the Qt High DPI scaling
attributes since they must be applied before QApplication
instantiation.

Enable this by checking for the presence of a static void initMain()
function on the test object and invoking it before QApplication
instantiation.

Prototypically use it in tst_qtimer and to turn off High DPI scaling for
tst_QGL.

[ChangeLog][QtTestLib] It is now possible to perform static
initialization before QApplication instantiation by implementing a
initMain() function in the test class.

Change-Id: Idec0134b189710a14c41a451fa8445bc0c5b1cf3
Reviewed-by: Volker Hilsheimer <volker.hilsheimer@qt.io>
Reviewed-by: Paul Wicking <paul.wicking@qt.io>
Reviewed-by: Edward Welbourne <edward.welbourne@qt.io>

1 files changed, 7 insertions, 0 deletions

diff --git a/tests/auto/opengl/qgl/tst_qgl.cpp b/tests/auto/opengl/qgl/tst_qgl.cpp
index 053c4b026b..3cc9592fb1 100644
--- a/tests/auto/opengl/qgl/tst_qgl.cpp
+++ b/tests/auto/opengl/qgl/tst_qgl.cpp
@@ -60,6 +60,8 @@ public:
     tst_QGL();
     virtual ~tst_QGL();
 
+    static void initMain();
+
 private slots:
     void initTestCase();
     void getSetCheck();
@@ -101,6 +103,11 @@ tst_QGL::~tst_QGL()
 {
 }
 
+void tst_QGL::initMain()
+{
+    QCoreApplication::setAttribute(Qt::AA_DisableHighDpiScaling);
+}
+
 void tst_QGL::initTestCase()
 {
     QGLWidget glWidget;