Capture specific logging output into a QString

[Asperamanca]

I enabled the following logging category to get some basic information about the scenegraph setup:
`QLoggingCategory::setFilterRules("qt.scenegraph.general=true");
This gives me an output like

qt.scenegraph.general: opengl texture atlas dimensions: 512x512
qt.scenegraph.general: R/G/B/A Buffers:   8 8 8 8
qt.scenegraph.general: Depth Buffer:      24
qt.scenegraph.general: Stencil Buffer:    8
qt.scenegraph.general: Samples:           0
qt.scenegraph.general: GL_VENDOR:         Google Inc.
qt.scenegraph.general: GL_RENDERER:       ANGLE (Intel(R) UHD Graphics 630 Direct3D11 vs_5_0 ps_5_0)
qt.scenegraph.general: GL_VERSION:        OpenGL ES 2.0 (ANGLE 2.1.0.57ea533f79a7)
...

I'd like to redirect this output to a string, so I can add it to a diagnosis information file. However, the only way I know so far is to use qInstallMessageHandler, which would capture other debug messages as well.

How can I selectively capture the scenegraph info, but not other debug messages?

[JonB]

@Asperamanca
So far as I know: yes you use qInstallMessageHandler, use the QMessageLogContext to check the category name, do what you want with your category, call the old message handler for other stuff.

[Asperamanca]

@JonB said in Capture specific logging output into a QString:

QMessageLogContext

According to Qt docs, QMessageLogContext does not have a public interface, and may only provide information in debug builds.

[JonB]

@Asperamanca
I did not test/look into it further, but I saw e.g. https://stackoverflow.com/questions/29646942/qmessagelogcontexts-fields-like-file-function-line-empty-or-zero

void action(QtMsgType type, const QMessageLogContext &context, const QString &msg)
{
      ts << context.file << ":" << context.line << ":"
         << context.function << ": " << msg << endl;
}

so it seems to be accessing QMessageLogContext fields. The reply there talks about debug/release builds.

Your documentation link is https://doc.qt.io/qt-5/qmessagelogcontext.html. But if you look at, say, https://doc-snapshots.qt.io/qt5-5.12/qmessagelogcontext.html you see the various fields described, including const char *category. That's all I know!