Question

What I am trying to do – Make a JNI call to a shared library written in Qt. On the C++ side I am using QPainter and QSvgRender to manipulate an svg image and return a simple QImage.

QImage im;
QPainter painter;
if("image/svg+xml" == mimeType) {
    QSvgRenderer svgrenderer(ar);
    im = QImage(static_cast<int> (svgrenderer.defaultSize().width()),
                static_cast<int> (svgrenderer.defaultSize().height()),
                    QImage::Format_ARGB32);
    im = im.scaled(QSize(50,50), Qt::KeepAspectRatio);
    im.fill(0);
    painter.begin(&im);
    svgrenderer.render(&painter); //Crashes here
}

What is the issue –
The code crashes while calling render as shown. And it crashes only for certain SVG images.

If I run the code within a stand alone Qt Application, it works fine.
I hadn’t created a QApplication instance within my shared lib as against a stand alone Qt App.
So I decided to create one this way-

From Java Main Thread – Spawn another thread which makes a JNI call to create a QApplication. Runs exec().

From Java Main Thread continue to make other JNI calls after the QApplication is initialized.

This still doesn’t work. Any advise on what I may be doing wrong and what is the right way to do what I am trying to do?
I have searched the forum and the web for solutions but nothing has helped. The only thread that came close to what I need is – http://developer.qt.nokia.com/forums/viewthread/2283 [developer.qt.nokia.com].

The whole thing runs inside a java based web container.

Answer 1

Kind of solved the crashing issue. Seemed to be a bug in Java 1.5 that I was using https://bugs.java.com/bugdatabase/view_bug?bug_id=5102720

I have fixed it for now by changing qt to make up for the stack realignment issue by adding these flags for qmake-

QMAKE_CFLAGS += "-mstackrealign"
QMAKE_CXXFLAGS += "-mstackrealign"

The problem was mainly on windows.