[Qt-interest] QGraphicsView and OpenGL rendering artifacts on Mac OS X

[John Clayton (gmail)]

I just adjusted my code to remove the QSplitter entirely from the  
program, so that my opengl based QGraphicsView is in a flow layout  
along with two other widgets.

The QGraphicsView still flickers horribly when its being redrawn (but  
always eventually draws itself correctly).

So I'm very much hoping someone has an idea what I could do to help  
solve the flicker.

--
John Clayton

On 9/08/2009, at 1:03 PM, John Clayton (gmail) wrote:

> And of course, having a link to the promised screen shots would help;
>
> http://gallery.me.com/john_clayton#100372
>
> --
> john
>
> On 9/08/2009, at 1:01 PM, John Clayton (gmail) wrote:
>
>> Hi All,
>>
>> I'm rendering a quad into a scene via opengl, and have a redraw  
>> issue that I [so far] haven't been able to track down, or solve.
>>
>> The Problem:
>> When resizing the opengl based qgraphicsview - the newly exposed  
>> edges are filled with rubbish before finally being redrawn  
>> correctly.  In this case, the non-scientifically measured delay  
>> before the view is finally redraw is somewhere in the vicinity of  
>> 200 milliseconds (i.e. gut feel).
>>
>> My Questions:
>> 1) Why am I seeing redraw artifacts in a double-buffered GL view?
>> 2) Why does the view eventually redraw itself correctly after what  
>> feels like 200-ish milliseconds.
>>
>> I've got a couple of screen shots in a gallery, showing the results  
>> of these artifacts.  The artifacts show up when the GL content is  
>> resized via a QSplitter - I don't know if having the OpenGL based  
>> QGraphicsView embedded in a splitter is the cause of this.  The  
>> track view in the shots redraws correctly all the time, but its not  
>> open-gl based.
>>
>> Has anyone encountered something like this before, if so - any  
>> ideas how I can fix it?
>>
>> the code to set up the previewView (QGraphicsView) is as follows:
>>
>>     QGLFormat fmt;
>>
>>     PreviewGLWidget* viewport = new PreviewGLWidget(fmt);
>>     _ui->previewView->setViewport(viewport);
>>
>>     viewport->makeCurrent();
>>
>>     _contentLoader = new ContentLoaderController(_document- 
>> >project, viewport);
>>     _previewScene = new PreviewScene(_document, _contentLoader);
>>
>>     _ui->previewView- 
>> >setViewportUpdateMode(QGraphicsView::FullViewportUpdate);
>>     _ui->previewView->setDragMode(QGraphicsView::ScrollHandDrag);
>>     _ui->previewView->setCacheMode(QGraphicsView::CacheNone);
>>     _ui->previewView- 
>> >setResizeAnchor(QGraphicsView::AnchorViewCenter);
>>     _ui->previewView- 
>> >setTransformationAnchor(QGraphicsView::AnchorViewCenter);
>>     _ui->previewView->setAlignment(Qt::AlignCenter);
>>     _ui->previewView- 
>> >setRenderHints(QPainter::HighQualityAntialiasing |  
>> QPainter::SmoothPixmapTransform);
>>     _ui->previewView->setScene(_previewScene);
>>     _ui->previewView->setBackgroundBrush(Qt::black);
>>     connect(_previewScene, SIGNAL(selectionChanged()), this,  
>> SLOT(slotPropagatePreviewSelectionStateToTrackView()));
>>
>> Any tips appreciated, thanks for your time/help.
>>
>> --
>> John Clayton
>

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