[vtkusers] QVTKOpenGLWidget - update() or GetRenderWindow()->Render()

Tue Jun 19 11:52:51 EDT 2018

Den tis 19 juni 2018 17:51Elvis Stansvik <elvis.stansvik at orexplore.com>
skrev:

> Aha, thank you both for the clarification/tip.
>
> I had hoped that there was a way in VTK to request a re-render to occur
> once control returns to the Qt event loop, instead of the immediate
> Render().
>
> That way an application could afford to be "sloppy" and request a
> re-render multiple times during the processing of a single event, but it
> would in the end only result in a single re-render.
>
> The ITK help class I guess could help
>

*CTK

Elvis

here, but I'm always weary of bringing in additional dependencies. Thanks
> for the tip though, we may end up using it.
>
> My endeavour was not to solve any identified problems in our app. I just
> wrongly though that calling Render was discouraged in favor of update(), so
> was wondering why it didn't work.
>
> I may go with the do nothing approach now that I know that Render is not
> bad per se.
>
> Elvis
>
> Den tis 19 juni 2018 17:32Andras Lasso <lasso at queensu.ca> skrev:
>
>> You can use CTK's ctkVTKAbstractView class to handle this. It has
>> scheduleRender method, which you call any time something might have changed
>> in your pipeline. Actual rendering will not happen more frequently than the
>> specified maximumUpdateRate.
>>
>>
>> https://github.com/commontk/CTK/blob/master/Libs/Visualization/VTK/Widgets/ctkVTKAbstractView.h#L77
>>
>> Andras
>>
>> -----Original Message-----
>> From: vtkusers <vtkusers-bounces at public.kitware.com> On Behalf Of
>> Utkarsh Ayachit
>> Sent: Tuesday, June 19, 2018 10:38 AM
>> To: Elvis Stansvik <elvis.stansvik at orexplore.com>
>> Cc: vtk <vtkusers at vtk.org>
>> Subject: Re: [vtkusers] QVTKOpenGLWidget - update() or
>> GetRenderWindow()->Render()
>>
>> Elvis,
>>
>> The best practice is indeed to call Render() when data has changed.
>> While making QVTKOpenGLWidget (which is called QVTKOpenGLSimpleWidget in
>> master) do a `RenderWindow::Render` in paint may seem like a good behavior
>> (as we indeed did initially), it so happens that the paint gets called way
>> too frequently e.g. if a tooltip or a menu pops  up.
>> Doing these potentially expensive renders in each `paint` is not
>> necessary since QVTKOpenGLWidget caches the last rendered image and can
>> simply `blit` it to the active frame buffer to satisfy Qt. Hence we opted
>> to let the application decide when scene has truly changed and call Render
>> explicitly to indicate that.
>>
>> Hope that clarifies things.
>>
>> Utkarsh
>> On Tue, Jun 19, 2018 at 10:20 AM Elvis Stansvik <
>> elvis.stansvik at orexplore.com> wrote:
>> >
>> > Hi all,
>> >
>> > I was looking over calls to Render() in our application, trying to
>> replace them with update() which I think is a "nicer" way of requesting a
>> re-render (?).
>> >
>> > But it seems to not be a drop-in replacements since it seems sometimes
>> update() doesn't cause a re-render (not even when control returns to the
>> event loop).
>> >
>> > So then I looked again at the docs for QVTKOpenGLWidget, and they say:
>> >
>> >     "An alternative is to call update() on the widget instance to
>> trigger a render once the context gets validated"
>> >
>> > It was this that sort of guided me to try to use update() instead of
>> Render().
>> >
>> > But then I found e.g. this commit:
>> >
>> >     "
>> https://na01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fgitlab.kitware.com%2Fvtk%2Fvtk%2Fcommit%2F4c77c46025e737ad66e0b797a759e73d81c9f240&data=02%7C01%7Classo%40queensu.ca%7C2c47a8aa57ee44de212b08d5d5f25ffa%7Cd61ecb3b38b142d582c4efb2838b925c%7C1%7C0%7C636650159330792727&sdata=8m7aw0XcHhoXg5h%2BH%2FnywEEfXlSKd04Fc3%2F2wKRcaRc%3D&reserved=0
>> "
>> >
>> > The commit message says: "QVTKOpenGLWidget now relies on VTK
>> applications calling `Render` on the window when data or rendering has
>> changed.".
>> >
>> > So now I'm a little confused: What is the correct way to request a
>> re-render once control returns to the event loop? Or must we always call
>> Render()?
>> >
>> > I'm talking now about the QVTKOpenGLWidget that is in 8.1.1, not the
>> new one that is in master (though I guess the best practice should be the
>> same for the two?).
>> >
>> > Many thanks in advance,
>> > Elvis
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