[Interest] Using Qt as backend for plugin to be loaded on a host software

[Konstantin Tokarev]

16.09.2015, 16:37, "Nuno Santos" <nunosantos at imaginando.pt>:
> Hi.
>
> I’m developing a plugin to be loaded by a music software host (VST). There are some lighter alternatives to provide graphics, network and other kinds of useful resources but I want to use Qt. I simply Love Qt!

I cannot help you with your questions, but I'd like to warn you that if somebody else loves Qt as much as you do (i.e., creates another VST plugin with Qt), host may crash if someone loads two such plugins with different Qt versions.

>
> When the plugin is open by the host, it provides a window ref to the plugin. On Window it is a HWND handle, on Mac it is supposedly a WindowRef.
>
> I have a working prototype for Windows. I don’t think it is all correct but its working. When the plugin is first started I check for the existence of a QApplication and start one if not.
>
> Then I create the main controller for my plugin and the QQuickView to draw on the window. To create the QQuickView i’m first creating a QWindow with the ptr to HWND handle as parent:
>
> window = QWindow::fromWinId((WId)ptr);
>
> view = new QQuickView(window);
> view->setSource(QUrl("qrc:/qml/vstmain.qml"));
> view->rootContext()->setContextProperty("controller", _controller);
> view->show();
>
> This is actually working quite well on Windows. The same strategy however, doesn’t work on a Mac. When I try to create a QWindow::fromWinId the result is a crash with the following stack trace:
>
> 2015-09-16 14:26:18.526 Live[91339:1091079] -[NSHIObject setPostsFrameChangedNotifications:]: unrecognized selector sent to instance 0x19806da0
>
> - The first question is: what is QWindow::fromWinId is expecting to be able to create a window? An NSView?
>
> - The second question is: the stack trace says that NSHIObject didn’t recognized the selector setPostsFrameChangedNotifications. What is a NSHIObject? I can only find references to HIObject from the HIToolbox and that belongs to the Carbon frame work. So far I haven’t been able to call Carbon methods inside my Qt environment even referencing -framework Carbon
>
> - Third question: On window I have an issue with the QApplication args and argv. On debug, there is an ASSERT that says that origArgc is different from the actual argc/argv. On release mode it crashes. Why does QApplication needs to receive the exact same arguments as the initial app?
>
> - Fourth question: how should I keep my run loop running without depending on the host? On Windows I have created a windows thread to call qApp->exec(). Although a warning that exec should be called on main thread it WORKS! How safe is this? Is there any other recommended option? What about Mac OS X?
>
> I have been google a lot specially about the NSHIObject and I can’t find an answer, not even a simple lead. The closest I have is vstgui, a GUI framework for VST plugins that has open source code and support for Carbon and Cocoa backends but the NSHIObject is intriguing me because I can’t find any explicit reference on how to deal with it.
>
> Any thoughts would be high appreciated.
>
> Thanks in advance,
>
> With my best regards,
>
> Nuno
> ,
>
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-- 
Regards,
Konstantin