I am developing a mixed C++/QML application using
qt-opensource-windows-x86-msvc2012_opengl-5.3.2 (and 5.4.0-beta).
The QML GUI contains a zoomable Canvas item embedded in a ScrollView.
Zooming the Canvas changes its size, and after experiencing some strange
crashes of the application during zooming, I researched the reason for the
crash
and found out that it crashed in QImage::detach():
void QImage::detach()
{
if (d) {
if (d->is_cached && d->ref.load() == 1)
QImagePixmapCleanupHooks::executeImageHooks(cacheKey());
if (d->ref.load() != 1 || d->ro_data)
*this = copy();
--> ++d->detach_no;
}
}
... because copy() failed (because malloc failed) and d was 0 and led to a
null pointer access.
This is a bug in QImage that should be fixed.
The reason for the failure lies in QQuickContext2DTexture which has the
QImage members m_image and m_displayImage with the size of the Canvas item.
If the user zooms in and out a lot those members a recreated a lot with
changing sizes which leads to cathastrophic memory fragmentation and finally
to a malloc failure.
The only (hacky) solution I could find so far is to use a big fixed size
(maximum) Canvas and fake the logical size for the ScrollView.
Any other ideas or some fix for QQuickContext2DImageTexture?
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