I have two QGraphicsView and one QGraphicsScene. One of views don't need to draw qraphicsitems. Is there any way to disable drawing of items on the view?
From the Qt5.2 documentation:
updatesEnabled : bool
This property holds whether updates are enabled.
An updates enabled widget receives paint events and has a system background; a disabled widget does not. This also implies that calling update() and repaint() has no effect if updates are disabled.
You'll probably have to show some code. There are quite a few ways to do this but it's really based on your implementation.
So one of the most simple ways to not draw items - set flag QGraphicsView::IndirectPaint for graphics view and overload drawItems methods in scene and view. Works for me.
Related
I've a QTreeWidget and need to disable the mouse over highlighting on the childItems but not the click selection. The point here is, that I need to set this per Item because some are selectable. I was thinking about the QTreeWidget::itemEntered signal to check if the item should be highlighted or not but I can't get it to work because the description says
QTreeWidget mouse tracking needs to be enabled for this feature to
work.
and I can't figure out how.
So my questions for are: How can I enable mouse tracking?
Is there an easier way to disable the highlighting?
Simply invoke setMouseTracking() to enable mouse tracking for a specific widget.
I ran into this problem (I know this is an old post, but I might as well post my solution, since it can be useful for others).
I could not properly disable the mouse feedback while keeping the mouse tracking enabled, but I could make this feedback invisible. I'm using qss stylesheets, and I set the mousehover feedback color to transparent:
MyTreeWidget::item:hover {
background-color: transparent
}
It did the trick for me. Sadly it makes the feedback invisible all the time, rather than allowing to turn it off and on.
So as a next step, for when I needed it, I implemented my own feedback by using a delegate and overwritting the paint function.
The QTreeView overwrite mouseMoveEvent and sends mouse coordinates to the delegate. This way, the delegate can adapt what it does in paint to this position. It feels pretty heavy, and a bit dirty, but it works. Delegate should also allow to have different behavior for different items.
PS: If you're using a delegate, in most cases, that should be enough without the qss change. In my case it wasn't, because I call QStyledItemDelegate::paint in my overwritten paint method, so I inherited some unwanted behavior.
I have a drawing that is built inside a QGraphicsScene with several layers of QGraphicsItem derived objects.
I am repositioning the QGraphicsItem objects based on some parameters and have noticed that there are some "ghost" trails left unless I call graphicsArea->viewport()->update(). I am repositioning the QGraphicsItem objects quite frequently (i.e. when a slider is moved) and updating the viewport only works if I call it manually some time after drawing is finished (e.g. on a button click).
One possible solution that I found was to fill the background of each QGraphicsItem to be a neutral colour. This doesn't work when I have overlapping items though, as the underlying items can get overwritten.
Does anyone have any suggestions?
Thanks,
Alan
I have a collection of images, dynamically generated through QGraphicsView widgets, and i'd like my users to choose between them. For that purpose, i would display inside a custom widget available images in some kind of grid and have users click the one they are interested in.
Multiple questions arise :
is there an existing widget that already fits this purpose ?
should i find a way to disable all mouse event handling by QGraphicsView items, or could i add a transparent widget in front of graphic views which would intercept them ?
is there a performance issue displaying many QGraphicsView widgets (up to a few hundreds) ? Should i export them to plain images first ?
First off, no, there's no widget designed specifically for that purpose.
I don't think you are grasping what QGraphicsView is for. It's for displaying a QGraphicsScene, which is meant to hold many QGraphicsItems. Based on your post, I can't see why you would need multiple QGraphicsViews. You can simply have one QGraphicsView and display many images inside of its scene. For example, see QGraphicsPixmapItem.
You definitely should not have hundreds of QGraphicsViews. You probably just want one (although a few could be justified in certain circumstances), in which you display many QGraphicsItems in a QGraphicsScene. You can definitely have hundreds of QGraphicsItems visible at once. In your case, you probably want QGraphicsPixmapItems, which are a subclass of QGraphicsItem. You could even have multiple QGraphicsScenes, and display whichever one is relevant using QGraphicsView::setScene. If you want the user to be able to select an image from a grid, and then work with that image, I would look to the State Pattern.
I can't think of any reason to disable mouse handling in QGraphicsViews, QGraphicsScenes, or QGraphicsItems. Why should these not handle their own mouse events? You can (and should, where necessary) subclass them and reimplement mousePressEvent, mouseMoveEvent, mouseRelease event, etc. to obtain the functionality you want.
Good luck!
I'm writing an image viewer as a custom Qt widget (see: https://github.com/dov/Qviv) and I now got stuck on the question of how to make my widget notify a parent QScrollArea of changes in the view port, and thus to tell it to move the scrollbars. E.g. if the image viewer changes the zoom factor as the result of a keypress then the scrollbars need to change their page size.
One way of doing it would be to have the widget explicitly check if the parent is a QScrollArea and then make an explicit call to its methods to notify it on any changes.
Of course I also need to connect the changes of the ScrollArea to the internal view of the image, but that is a different question. And I need to cut the infinite recursion where the widget reports changes to the scrollbar that report changes to the widget etc.
Edit 20:15 Wednesday (GMT/UTC) trying to clarify to Vjo and myself what I need.
What I am trying to achieve is the equivalent of a Gtk widget that has been assigned a pair of GtkAdjustment's that are connected to a horizontal and vertical scrollbar. In my widget GtkImageViewer, that QvivImageViewer is based on, whenever I change the view due to some internal event (e.g. a keypress) I update the GtkAdjustment's. The scrollbars are connected to such changes and are update accordingly. GtkImageViewer also listens to the GtkAdjustment changes, and thus if the user scrolls the scrollbars, the GtkImageViewer is updated with this information and can change its view. My question is whether there is anything similar to GtkAdjustment in Qt that you can connect to for changes, and update in which case the update will be propagated to all the listeners?
Thus I don't expect the ScrollArea to be part of QvivImageViewer, but if the user has placed QvivImageViewer within a ScrollArea, I want bidirectional communication with it so that the scrollbars reflect the internal state of the widget.
The simplest is to send the QResizeEvent event from your widget object to the QScrollArea object.
I finally downloaded the Qt sources and investigated how QTextEdit does it. What I found is that QTextEdit inherits the QAbstractScrollArea on its own, and thus the scroll area and the scrollbars are part of the widget. This is different from Gtk, which uses a higher level of abstraction, through its GtkAdjustment's that are used to signal changes between the scrollbars and the widget. The Qt model is simpler and this is the way that I will implement it in my widget.
It's been a while, but I ran across this same issue.
You can inherit QAbstractScrollArea if you'd like, but QScrollArea will work as well.
Your custom inner widget (i.e. the one that you are scrolling), should do the following when its size changes:
void MyCustomControl::resize_me() {
// recompute internal data such that sizeHint() returns the new size
...
updateGeometry();
adjustSize();
}
QSize MyCustomControl::sizeHint() {
return ... ; // Return my internally computed size.
}
I was missing the adjustSize() call, and without it the QScrollArea will ignore size changes of the internal widget.
I would like to add an effect of moving rows, like a store, in a QListView using QAnimation.
I use a custom delegate to render things from a QStandardItemModel.
My delegate is a custom widget.
The paint method in the delegate creates the widget, paints it and destroys it. I have no direct access to each custom widget displayed.
Nevertheless, I would like to use setPos() within the animation to move this "not accessible" widget.
Any ideas ?
Thank you
Your description of what you want to achieve is not very clear.
Have you thought of moving the animation into the QListView?
It should have visibility of all items in it's model.