@Dariusz Ok so you could get the 40K sample to lag also ?

Probably not the cleanest solution, but a workaround would be to use an eventFilter. The QGraphicsView could call widgetName->installEventFilter(this) Then in the QGraphicsView, you override the method "eventFilter". That should receive the event originally destined to your widget. Be careful, handling event coordinates can be a bit messy.

@mrjj Yes, it worked. Thank you!

@Another-Qt-Beginner Hi Did you try setting https://doc.qt.io/qt-5/qgraphicsview.html#ViewportUpdateMode-enum to FullViewportUpdate to see if that reduces the issues.

Hi, What exactly is not working ?

Also another problem with path.contains that I find is that the contains would use this as check area > https://doc.qt.io/archives/qt-4.8/images/graphicsview-pathitem.png Which means that the shape can be bigger/inaccurate comparing to the selection location... I think I will need to do some math and create another method for path click intersection. Ok I sorta managed to "fix" it... I ended up creating a forward and then reverse path during selection process. So that the path is a closed - precise - shape. This way I can get proper click detection, I still cant compute which path is closer, but at least selection works properly now.

@lansing I'm not sure what you are trying to achieve. Normally, I would calculate the correct bounding rect (and ideally cache the result as long as nothing changes, so calls to boundingRect() stay fast)

It appears that QGraphicsScene checks if position of item is visible in view and then draws/dont draws it... returning qgraphicsScene->sceneRect() as boundingRect on my curve "solved" the issues but its a problem for selectable items... hmmm

@SGaist Its about precision moves, if user wants to move by tiny bit, scaling mouse movement by x value would allow that to happen. Else he would have to type 0.0001 0.0002 0.0003 etc etc. I think I could handle it using itemChange() and record initial mouse click press/release and calculate delta using that.. Yep that seem to do the trick... I can now move my items by tiny amount and doing "Long precise drags" deltaX = (newPos.x() - self.mMousePressPosition.x()) / 2 newPos.setX(newPos.x() - deltaX) deltaY = (newPos.y() - self.mMousePressPosition.y()) / 2 newPos.setY(newPos.y() - deltaY) Small edit, function above works for "simple" items, but as soon as I get to child items with parent it appear to break... sigh. Needs some more math there

Hi I think you just broke GraphicsView normal handling. Try also calling base class mousePressEvent as it might use for the actual item selection void GraphicsView::mousePressEvent(QMouseEvent *event) { if(event->buttons().testFlag(Qt::LeftButton)) { int x,y; x = event->pos().x(); y = event->pos().y(); qDebug() << x << ", " << y; QPointF point = mapToScene(x, y); QGraphicsEllipseItem *ellipse; ellipse = scene->addEllipse(point.x(),point.y(),5,5,QPen(Qt::red), QBrush(Qt::red)); ellipse->setFlag(QGraphicsEllipseItem::ItemIsMovable); } // call base class QGraphicsView::mousePressEvent(event); }

@sgaist Hmmmmmmmmm I wrote a little routine to use mouse press/release to see what has changed to determine my selection but it does not work as well as I wish. But I missed that focusItemChanged mhmhmhmh thanks! Will go over it again :- )

I've updated the question with gif/some updates... Still fighting with it o.o I think by using int vertOffset = horizontalScrollBar()->sliderPosition(); I can somehow calculate the "jump" value offset and offset position of line by that. Not sure how yet tho...

Hi, Without more details form you side, it looks like that's the function you are looking for.

Call fitInView on the GraphicsView with the Image whenever the size of the GraphicsView changes. The rest should work automatically.

@Skamath The Halcon example using Qt is very simple but it uses the Halcon Graphics Window to show images, regions and XLDs. If you think that it is complicated I recommend you to use the Halcon Graphics Window instead of trying to build your own Graphics Window based on QGraphicsView.

Thanks @SGaist and @raven-worx , I try both methods to see which one to use better in my program.

@Staslend if your issue is solved, please don't forget to mark your post as such! Thanks.

Hi, You should add: Which version of Qt you were using before Which version of Qt you are using now Graphics card + driver Platform you are running on

The idea is that you have your container widget getting resized and in its resize event, you change the size of the inner widgets with the ratio you want.

@Niagarer Good found. :)

Thanks for the input! I think I'm going to go with QGraphicsView for the notation and use QQuickWidgets throughout the other pieces of the UI that don't need access to the entire model. I'm hoping that won't be too complicated and will give me the best of both worlds. But I do wonder: is there a specific piece of Qt Quick that's supposed to a "replacement" for QGraphicsView? It seems like the scene graph is a bit too low level, but it's also the only way to gain a lot of control and keep things mostly on the C++ side. It would be nice if the built-in QML elements are exposed via a C++ API at some point.

@mrjj There are other obstacles that I need to overcome. But this way seems to be the solution that i am implementing. Thanks

Do you mean custom graphicsView or tableView? If custom graphics view wouldn't it be too hard to reimplement everything? Any links or example would help.

In your MyView::paintEvent write QPainter painter(viewport()); instead of QPainter painter(this);.

@Nico1564 said in How to draw on Image loaded in a QGraphicsView: Yeah i know that this work but i need to draw with fonctions. I successed to do that but I don't want to have the GraphicsView at the beginning of the program, and i want to add draws like an Ellipse (and the image) when i click on buttons. These lines could just as well happen inside a button click QGraphicsEllipseItem* testItem = new QGraphicsEllipseItem(20,30,120,70,0); m_pScene->addItem(testItem); In that case, you would create an ellipse every time you pressed that button. I don't quite understand the "I don't want to have the GraphicsView at the beginning of the program" - maybe you could elaborate on that.

Hi and welcome to devnet, What version of Qt are you using ? On what OS ? Which architecture ? What type of image is that ?

Hi, You shouldn't use the size of a widget in its own constructor. The widget being not yet visible, the value won't make sense.

@SGaist Thanks for suggesting OpenGL, I think that might be a possibility at some point. As of now, I got it to work by locking the UI updates and batch repainting all of the windows at once: for(auto widget : qApp->topLevelWidgets()){ widget->setUpdatesEnabled(true); } qApp->processEvents(); for(auto widget : qApp->topLevelWidgets()){ widget->setUpdatesEnabled(false); } I know this may not be the best way to achieve this, so I am all ears if there's any better way to limit UI updates to a single point in execution. Thanks!

Hi and welcome to devnet, Since your widgett is called PixmapView then in your CanvaTest class you can use ui->PixmapView ..

Hi and welcome to devnet, Did you try with QStackedLayout with StackingMode set to StackAll ? Hope it helps

Hi, I wouldn't say an oversight but likely you have a use case that has not happened before. Also QOpenGLFramebufferObject is a pretty new class compared to QGraphicsView. I'd recommend brining this to the interest mailing list. You'll find there Qt's developers/maintainers.

What do you think about this? int length = this->boundingRect().width(); length = (int)(((double)length * (double)value) / 100.0); QPixmap pix(this->boundingRect().width() - length, this->boundingRect().height()); pix.fill(Qt::transparent); QPainter p; p.begin(&pix); p.fillRect(pix.rect(), QColor(0, 0, 0, 120)); p.end(); gauge->setPixmap(pix); gauge->setPos(pos().x()+length, pos().y()); It works fine and the effect is the same as on example pixtures above.

:D I haven't had much time to test if the bug exists in Qt5. I'll check it out and update the topic accordingly. If the bug is still there, of course, I will submit the fix. Thanks for your time.

Hi and welcome to devnet, Do I understand correctly that you want to run your FPS at 100Hz ? In any case, you'll have to go OpenGL (QWindow and friends)