[Qt-interest] UI Interaction Freezing when using QGraphicsView - How to Debug?

[Josiah Bryan]

David Boosalis wrote:
> I ran your code on my Linux system which has an inferior cpu (AMD Athlon 
> X2) and a cheap built in graphics card on motherboard.  Saw really flaky 
> and randon behavior.  SOmetimes I saw what you saw, other times I 
> started it and it ran ok, albeit very slot
> 
> If I did not use the OpenGL widget it ran a lot better, but still very 
> bad for only 100 objects, then looked at Chips example n qt/demos which 
> has probable a 1000 items I think.  I used there settings for 
> QGraphicsView and also switched to QGraphicsRectItem and things ran very 
> smooth.
> 
> By the way, your code ran just as bad under Qt 4.6-tp1. 
> 
> The code below ran very well. Maybe someone else can comment on how to 
> tweek Messa or OpenGL, but heck if it this sensitive to the openGL 
> driver might as well let Qt do the rendering and know it run adequately 
> on any machine.   I hope someone  can diagnose the opengl issue here
> 

David -

Thanks for your confirmation that its not all just in my head. I agree, 
this seems to be a serious issue with opengl/Qt interaction. I applied 
your QGraphicsView optimizations below and it does indeed seem to 
improve performance to some degree.

However, my app's demands on the system seem to cry out for OpenGL's 
acceleration - can anyone at trolltech confirm this problem? Any leads 
on how to get this fixed or looked at?

Thanks!
-josiah




> 
> class BoxItem : public QGraphicsRectItem
> {
> public:
>    
>     QRectF m_contentsRect;
>     QPen pen;
>     QBrush brush;
> 
> 
>   BoxItem(QGraphicsScene * scene, QGraphicsItem * parent) :
>     QGraphicsRectItem(0,0,500,500,parent)
>   {
>         setFlags(QGraphicsItem::ItemIsMovable);
>         setBrush(QColor(255,0,0,255));
>         pen.setWidthF(3);
>         pen.setColor(QColor(0,0,0,255));
>   }
> };
> 
> int main(int argc, char **argv)
> {
>     QApplication app(argc, argv);
>    
>     QGraphicsView *graphicsView = new QGraphicsView();
>      //graphicsView->setViewport(new 
> QGLWidget(QGLFormat(QGL::SampleBuffers)));
> 
>     graphicsView->setCacheMode(QGraphicsView::CacheBackground);
>     
> graphicsView->setViewportUpdateMode(QGraphicsView::BoundingRectViewportUpdate);
> 
>     graphicsView->setInteractive(true);
>     QGraphicsScene * scene = new QGraphicsScene();
>     scene->setBackgroundBrush(QColor(100,100,100));
>     graphicsView->setScene(scene);
>     scene->setSceneRect(0,0,800,600);
>     graphicsView->resize(800,600);
>     graphicsView->setWindowTitle("Test");
>     graphicsView->setRenderHint(QPainter::Antialiasing, false);
>     graphicsView->setDragMode(QGraphicsView::RubberBandDrag);
>     graphicsView->setOptimizationFlags(QGraphicsView::DontSavePainterState);
>     graphicsView->setViewportUpdateMode(QGraphicsView::SmartViewportUpdate);
>    
>     for(int i=0;i<100;i++)
>     {
>         BoxItem *x = new BoxItem(scene,0);
>         x->show();
>         x->setBrush(Qt::red);
>         x->setPos(qrand() % 800, qrand() % 600);
>         scene->addItem(x);
>     }
>    
>     graphicsView->show();
>    
>     return app.exec();
> }
> 
> On Fri, Sep 18, 2009 at 5:24 PM, Josiah Bryan 
> <jbryan at productiveconcepts.com <mailto:jbryan at productiveconcepts.com>> 
> wrote:
> 
>     Josiah Bryan wrote:
>     ...
> 
>         Its a rather extreem freeze - in fact, even the system mouse
>         freezes (under gdb, when not running in gdb, mouse doesn't
>         freeze but unrelated apps still do, like the charts in gkrellm.)
> 
>     ...
> 
>     Alright, it took 4+ hours, but I narrowed it down to the attached
>     test case.
> 
>     To reproduce:
> 
>     - Build and run
>     - Attempt to drag any rectangle, even by a small amount.
>     - Repeat until system becomes unresponsive (mouse freezes, other
>     programs freeze.)
> 
>     On my system (specs below), the program freezes within 1 - 5 mouse
>     interactions (drags.) This is with the both cores hovering around 5
>     - 10% load before mouse interaction following program launch. RAM is
>     around 1.5GB free at time of tests, disk usage minimal (~64K/sec
>     xfer load.) No other graphic intensive programs running - email,
>     terminals, KWrite, etc. No other opengl programs (that I know of) -
>     certainly no 3D programs.
> 
>     System info:
> 
>     Running with 4GB RAM on an Intel(R) Core(TM)2 Duo CPU, both cores
>     running at 3.00GHz. Graphics card is a Quadro NVS 290 (PCIe card)
>     with 256 MB RAM.
> 
>     X -version reports:
> 
>     X Window System Version 1.3.0
>     Release Date: 19 April 2007
>     X Protocol Version 11, Revision 0, Release 1.3
>     Build Operating System: Fedora Core 7 Red Hat, Inc.
>     Current Operating System: Linux josiah-desktop.pci.local
>     2.6.23.9-85.fc8 #1 SMP Fri Dec 7 15:49:59 EST 2007 i686
>     Build Date: 17 October 2007
>     Build ID: xorg-x11-server 1.3.0.0-33.fc8
> 
>     NVidia control center reports under "OpenGL/GLX Information",
>     heading "Server GLX Information", that the vendor is NVIDIA, version
>     1.4, with the following extensions:
> 
>     GLX_EXT_visual_info
>     GLX_EXT_visual_rating
>     GLX_SGIX_fbconfig
>     GLX_SGIX_pbuffer
>     GLX_SGI_video_sync
>     GLX_SGI_swap_control
>     GLX_EXT_texture_from_pixmap
>     GLX_ARB_multisample
>     GLX_NV_float_buffer
>     GLX_ARB_fbconfig_float
>     GLX_EXT_framebuffer_sRGB
> 
> 
>     Tested on XP - not able to reproduce there. No other linux machines
>     tested yet. Will test my home system this evening (CentOS 5.2, dual
>     head, etc.)
> 
>     Anyone able to reproduce or offer tips on fixing? Anyone at
>     trolltech able to comment?
> 
>     Thanks in advance.
>     -josiah