[Automotive] QmlLive: Is LiveNodeEngine::RecreateView mode really needed?

[Martin Kampas]

Hi Jürgen,

> We currently never use a QQuickView and normally require the root item to be a Window or if not to create a Window and reparent the item.

Does this mean you do not actively use the embedded in-bench view nowadays? IIUC loading a QML component with Window as the root item always creates a separate window, not embedded in the bench.

BR,
Martin

________________________________
From: Juergen Ryannel [juergen.bocklage-ryannel at pelagicore.com]
Sent: Tuesday, August 09, 2016 9:43 PM
To: Martin Kampas
Cc: automotive at qt-project.org; Dominik Holland
Subject: Re: QmlLive: Is LiveNodeEngine::RecreateView mode really needed?

Hi Martin,

Thanks for the proposal, sounds exactly like I would like to go forward with. I would even like to get ride of the QQuickView altogether (so on (3) not even optional. We currently never use a QQuickView and normally require the root item to be a Window or if not to create a Window and reparent the item.

I’m currently on holiday, but I’m happy to review your patches. Thanks for looking into this.

/ jryannel


On 09.08.2016, at 17:29, Martin Kampas <martin.kampas at jolla.com<redir.aspx?REF=6-yQkrNfDkaxtwPL2vE6wvyM57BRBC_OVdwhvffwtT05bbSpE8HTCAFtYWlsdG86bWFydGluLmthbXBhc0Bqb2xsYS5jb20.>> wrote:

Hi Jürgen,

> We had some issues where content (e.g. QML, images, …) where cached and survived a clearComponentCache call. [...]

You are right, images need additional handling in addition to clearComponentCache - there is QQuickWindow::releaseResources() which fixes it. Verified with a QML Image element https://codereview.qt-project.org/#/c/167483/<redir.aspx?REF=uFO-hgrs5YBl9zd6UF_xKZ5jarfnUwURuDO2WsHSvMo5bbSpE8HTCAFodHRwczovL2NvZGVyZXZpZXcucXQtcHJvamVjdC5vcmcvIy9jLzE2NzQ4My8.>

> Ideally we would not use a QQuickView at all and just depend on a QQmlEngine.

Also my opinion - proposed in my reply to Dominik Holland.

> Additionally we would like to create the out-of-process option, where we control a remote process. This makes it easier to survive crashes from C++ plugins.

I understand this feature to be rather orthogonal to the mechanism of reloading. Maybe as a last sort mechanism when things go bad. I would see it better to be implemented somewhere above LiveNodeEngine.

Here is my proposal I wrote in my reply to Dominik Holland extended w.r.t your comments:

I propose to

1) remove the RecreateView mode and only rely on QQmlEngine::clear/trimComponentCache() and QQuickWindow::releaseResources()
2) require to set QQmlEngine and make setting QQuickView optional (useless when the QML component instantiates QQuickWindow)
3) only after that fix memory leaks in LiveNodeEngine :)
4) remove the UpdateMode enum as no mode selection is needed anymore. Single implementation works in all cases; out-of-process control would be implemented as a feature orthogonal to the mechanism of reloading, not as another mutualy exclusive option.

If you agree I will contribute patches for this.

BR,
Martin

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