I've implemented a basic KisLogManager class with the ability to capture logging messages. It can be extended for use.

It already has the code to configure QLoggingCategory filters and get the logging messages, but more work is needed before it can be made more useful. Thread-safety is also not considered in the current code.

The relevant commit is 221f6415076c096bc7b68b60600d813d231547ec and it is on branch alvin/logging-capture. You can fork a branch off it and start working from there.

P.S. Here is a sample code snippet on using the current log capturing code:

{
    qDebug() << "test log capturing";
    QString dbgStr;
    QDebug dbg(&dbgStr);
    KisLoggingManager::ScopedLogCapturer logCapturer("qt.qpa.gl",
        [&dbg](QtMsgType type, const QMessageLogContext &context, const QString &msg) {
            dbg << "Captured Message type:" << type << ", Context:" << context.category << context.file << context.function << context.line << context.version << ", msg:" << msg;
            dbg << "\n";
        });
    {
        QGuiApplication app(argc, argv);
    }
    qDebug() << "Captured:\n" << dbgStr;
}

To manage the lifecycle a bit better, perhaps KisLoggingManager should be changed to a global "singleton"-like object initialized as a local variable within main(). This way it can automatically perform initialization and cleanup via the constructor and destructor, and reduce the amount of global static variables to just one.