[vtkusers] Advice on mitigating choppy resize with Qt 5 + VTK 7.1

[Elvis Stansvik]

2017-03-07 16:20 GMT+01:00 Elvis Stansvik <elvis.stansvik at orexplore.com>:
> 2017-03-07 16:10 GMT+01:00 Elvis Stansvik <elvis.stansvik at orexplore.com>:
>> 2017-03-07 15:58 GMT+01:00 Elvis Stansvik <elvis.stansvik at orexplore.com>:
>>> 2017-03-07 15:53 GMT+01:00 David Cole <DLRdave at aol.com>:
>>>> On Windows, we make resizing our windows interactive by getting the
>>>> vtkInteractorStyle associated with the render window containing the
>>>> volume rendering, and then calling StartState at resize begin time
>>>> (OnEnterSizeMove) and StopState at resize end time (OnExitSizeMove).
>>>>
>>>> I suppose there may be a Qt equivalent which works on many platforms
>>>> for beginning and ending a resize action. If not, there are definitely
>>>> platform-specific hooks you can intercept to achieve smooth resizing
>>>> with this technique.
>>>>
>>>> Wrapping anything in a StartState/StopState pair on the
>>>> vtkInteractorStyle will cause "interactive frame rate rendering" to be
>>>> in effect in between the calls. The volume rendering is not as nice
>>>> looking during interactions, but it is definitely speedier.
>>>
>>> Ah, I was just about to reply to myself with some further information:
>>>
>>> I know that during interaction, the quality of the rendering is
>>> decreased, and that this can account for some of the performance
>>> discrepancy I'm seeing between camera movement vs window resize.
>>>
>>> But, I've experimented with disabling the quality degradation during
>>> interactions (so that the two should be on "equal footing"), and the
>>> resizing is still much more choppy than when interacting with the
>>> camera. So there must be something else.
>>>
>>> In fact, in the screencast I showed, I wasn't using the volume
>>> renderer's default built-in quality degradation during interaction.
>>> I'm using my own since I've found that VTKs own is a little too
>>> aggressive in degrading the quality to maintain frame rate.
>>
>> To illustrate, look at the attached screen recording. In this test
>> case, I'm using
>>
>>     mapper->AutoAdjustSampleDistancesOff();
>>     mapper->SetSampleDistance(0.0002);
>>
>> on my vtkGPUVolumeRayCastMapper, to turn off the automatic adjustment
>> of sample distance during interactions, and hardcode the sample
>> distance to 0.0002.
>>
>> Notice how the rendering is still reasonably smooth during
>> interaction, but during resize, the rendering sometimes lags with 100s
>> of milliseconds. During the resizing I was getting warnings like
>>
>> Warning: In /buildbot/vtk7-builder/build/Rendering/OpenGL2/vtkXOpenGLRenderWindow.cxx,
>> line 1207
>> vtkXOpenGLRenderWindow (0x2a629d0): warning window did not resize in
>> the allotted time
>>
>> printed.
>
> I wonder if what I'm seeing may be related to
>
>     https://codereview.qt-project.org/?#/c/127006/
>
> That fix was unfortunately never merged to the 5.5 branch, but it was
> merged into Qt 5.6:
>
>     https://codereview.qt-project.org/#/c/140608/
>
> Too bad for me, since the app must work well with Qt 5.5.1 (Ubuntu
> Xenial-packaged version) :(
>
> I'd just like to hear if anyone else with Qt 5 + VTK 7 on Linux are
> seeing this poor behavior during resizing, or if I'm alone.

Sorry, ignore the above. In my last test case I did not use Qt at all,
just a render window + interactor. So it's not a Qt issue.

Elvis

>
> Elvis
>
>>
>> Elvis
>>
>>>
>>> Elvis
>>>
>>>>
>>>>
>>>> HTH,
>>>> David C.
>>>>
>>>>
>>>>
>>>> On Tue, Mar 7, 2017 at 9:33 AM, Elvis Stansvik
>>>> <elvis.stansvik at orexplore.com> wrote:
>>>>> 2017-03-07 15:17 GMT+01:00 Elvis Stansvik <elvis.stansvik at orexplore.com>:
>>>>>> Hi all,
>>>>>>
>>>>>> I'm using Qt 5.5.1 and VTK 7.1. The program has a couple of VTKWidget
>>>>>> showing volume renderings, as well as a window with a chart.
>>>>>
>>>>> Actually, I'm able to reproduce this behavior when not using Qt at
>>>>> all, but just a regular render window + interactor setup with a single
>>>>> volume rendered. Camera interaction is nice and fast, but resizing the
>>>>> window, the rendering is very choppy. I'm also getting
>>>>>
>>>>> Warning: In /buildbot/vtk7-builder/build/Rendering/OpenGL2/vtkXOpenGLRenderWindow.cxx,
>>>>> line 1207
>>>>> vtkXOpenGLRenderWindow (0x1353a10): warning window did not resize in
>>>>> the allotted time
>>>>>
>>>>> printed to the console, so it seems VTK detects what I'm seeing
>>>>> visually. I did not get this warning printed in the Qt + VTK app.
>>>>>
>>>>> Elvis
>>>>>
>>>>>>
>>>>>> Have a look at the attached screen recording. Notice how camera
>>>>>> interaction in both VTK render windows is nice and smooth, but when
>>>>>> resizing the windows, the updating of the renderings is very
>>>>>> slow/choppy.
>>>>>>
>>>>>> I've been trying to debug this, or at least finding a way of
>>>>>> mitigating it. Could it be that Qt is delivering too many resize
>>>>>> events? Has anyone else dealt with this problem?
>>>>>>
>>>>>> Thanks in advance for any advice,
>>>>>> Elvis
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