I've created an object Chartblock that implements QGraphicsItem. My goal is to create a grid of these objects, and when the mouse button is pressed (and held) and is drug over each block, perform something on each block as the cursor enters it.
Since a QGraphicsItem grabs the mouse events when it is clicked within it, other Items will not fire for the mouseMoveEvent. I then created an object based on the QGraphicsItemGroup to handle all the mouse events, but then I would need some way to pass mousePressEvent/mouseReleaseEvent as well as mouseMoveEvent to each child that the cursor is over.
Am I overthinking how to do this? It seems like such a simple action shouldn't be that difficult to create, but with QGraphicsItems holding onto the mouse events for itself, I'm not sure how to get around it. I've read similar situations, but nothing seems to give a straightforward answer.
Edit: I suppose a way to do this would keep track of the coordinates/sizes of every single QGraphicsItem I create in an array, then get the position of the cursor in the Group mouseMoveEvent, and see if there's a hit..
I was able to pull together a few similar answers to create a solution; I dropped the idea of placing all my QGraphicItem's in a Group, and placed them directly on a scene. With the scene grabbing all mouse events, I have the mouseMoveEvent check to see if the current position is on top of a QGraphicsItem - if so, perform something.
I still need to try and get itemAt() to work for my own classes that implement QGraphicsItem, as itemAt returns only QGraphicsItem's, but I'm sure some cast should get it working.
void ChartScene::mouseMoveEvent(QGraphicsSceneMouseEvent *event)
{
QPointF mousePosition = event->scenePos();
QGraphicsItem* pItem = this->itemAt(mousePosition.x(), mousePosition.y());
}
Related
I have a scene made up of objects, each with a different position. I also have 2–4 pawns I'd like to move to the position of the object clicked, not to the position of the event.
I tried doing something like event->pos() but that gives me the coordinates of the event. Is there any way to do this?
The method you're looking for is QGraphicsView::items().
I'm trying to create a detachable type style widget, like in the way Chrome tabs are detachable (class is called Tab). I have everything working, except for a bug where sometimes (maybe 50% of the time), the Tab object never gets the mouse release event, and stops getting mouse move events.
Essentially, the detaching system works by allowing drags in the mouse press/move/release functions, just like normal. The mouseMoveEvent checks the total distance moved from the start, and if over a certain amount, will start the "detaching" process. The detaching process involves setting the parent widget to 0 (top level widget, undecorated window), so the Tab object is pretty much floating above everything, under the mouse, and continues to be dragged along with it until released.
I ran through all the QEvent items being delivered, and I found that when this issue occurs, the QEvent::MouseMove items (and all mouse events after this) are being sent to the TabBar (the Tab object's original parent). This occurs directly after calling setParent(0) on the Tab.
Basic mouse handling overview:
void Tab::mousePressEvent(*) {
[set up some boolean, start positions, etc]
}
void Tab::mouseMoveEvent(*) {
[track the updated position]
if (positionChange > STATIC_AMOUNT)
detachTab();
}
void Tab::mouseReleaseEvent(*) {
[return the Tab to its original position, and set the parent back to the TabBar]
}
void Tab::detachTab() {
QPoint mappedPos = mapToGlobal(0, 0);
setParent(0); //The loss of MouseMove events occurs when this returns.
move(mappedPos);
show();
raise();
}
Here are the events that the Tab object receives (first row is QEvent type, second is the name)
[Tab::detachTab() started]
[setParent(0) started]
QEvent::Hide
QEvent::Leave
qApp QEvent::MouseMove [ TabBar ] <-- now the TabBar is soaking up the mouse events
QEvent::HideToParent
QEvent::ParentAboutToChange
QEvent::ParentChange
[setParent(0) returned]
....
Summed up: my draggable QWidget loses QEvent::MouseMove and QEvent::MouseButtonRelease events after having its parent set to 0.
Any advice would be really appreciated!
A bit tricky workaround. I didn't test it, it's just an idea.
When your mouse hovers draggable part of a widget you may create topmost widget (let's call it Shade) with Qt::FramelessWindowHint (and possible with Qt::WA_TranslucentBackground). You may manipulate with Shade apperance via reimplementing paintEvent. For example - draw content of original widget, or draw some transparent preview, etc.
Then you may resize a Shade during dragging, to show user that widget will be detached. You will not loose mouse capture.
When user release mouse - you remember position of Shade, destroy it and detach+move original widget.
Feel free to ask, if you want more details.
Here is similar question.
So you suppose to use QDocWidget and enforce stacking of this widgets using tabifyDockWidget.
I wish to make a custom graphics item to follow the cursor without needing to be clicked on. My view has setMouseTracking(true), my graphics item has setFlag(ItemIsMovable, true); setAcceptHoverEvents(true);, but it doesn't track the cursor, I have to click and drag it. What is the proper way to make a QGraphicsItem follow the cursor?
You can only capture mouse event on an item if your cursor pass above it. For example, instead of clicking on the item, you can react on mouseMove events.
But you seem to want a more global behaviour. You could track mouseMoveEvent directly on your QGraphicsView (or on your QGraphicsScene if you have multiple views) (see mouseMoveEvent). After that, just keep a reference on your item and make it move each time you intercept an event
I have a QPushButton with an image that has two areas that I want to handle differently when clicked. Due to the positioning on the image, I cannot really use separate buttons for the two images.
What I'd like to do is, in the slot where I am handling the click, have it check the coordinates of the click to determine which area was clicked.
Is there a way to access this?
This is what first comes to mind. It should work, although there may be a simpler way:
Create your own class that derives from QPushButton.
Override the necessary mouse events (mousePressEvent and mouseReleaseEvent) and, before calling the base class implementation, set a property in your object using setProperty with the position of the mouse click. (The position is available from the event parameter.)
In the slot handling the event, use sender() to get the button, and read the property using property().
If you don't need to treat your object as the base class (QPushButton*) you could just create a new signal that includes the mouse event and attach that to your slot. Then you wouldn't need the property at all.
You can get the current mouse position using QCursor::pos() which returns the position of the cursor (hot spot) in global screen coordinates.
Now screen coordinates are not easy to use, and probably not what you want. Luckily there is a way to transform screen coordinates to coordinates relative to a widget.
QPoint _Position = _Button->mapFromGlobal(QCursor::pos());
This should tell you where on the button the mouse was when the user clicked. And you can take it from there.
Building on #Liz's simple mechanism, here's what I did; this is in a slot method that is called on pressed() but generalizes to other situations. Note that using pushButton->geometry() gives you coordinates that are already in global space so you don't need to mapFromGlobal.
void MainWindow::handlePlanButtonPress()
{
int clickX = QCursor::pos().x();
int middle = m_buttonPlan->geometry().center().x();
if ( clickX < middle ) {
// left half of button was pressed
m_buttonPlan->setStyleSheet(sStyleLargeBlueLeft);
} else {
// right half of button was pressed
m_buttonPlan->setStyleSheet(sStyleLargeBlueRight);
}
}
I basically have 3 layers (Window > Scene > View) that each need to handle a mouseMove event without blocking the others. It seems only the youngest child is getting the event though. I was hoping I could process the event and then call event->ignore() to pass the event back up the stack, but it doesn't seem to be working.
Some relevant code if you need it:
void EditorWindow::createScene() {
m_scene = new EditorScene(this);
m_view = new EditorView(m_scene);
// ...
}
void EditorScene::mouseMoveEvent(QGraphicsSceneMouseEvent* mouseEvent) {
printf("B\n");
// ...
}
void EditorView::mouseMoveEvent(QMouseEvent* event) {
printf("C\n");
event->ignore();
}
Only "C" is being printed. Note that EditorScene and EditorView receive different types of mouse events so it's not completely trivial to pass them around.
The EditorWindow also needs the mouse coordinates; currently I'm sending a signal from one of the children which is caught by the window... but it shouldn't really be necessary to relay it that way, should it?
Found this nice article. Calling ignore() tells Qt to find another receiver. Sounds like it should work, but perhaps it means an unrelated receiver. The proper way to propagate it is actually to call BaseClass::Event like so:
void EditorView::mouseMoveEvent(QMouseEvent* event) {
QGraphicsView::mouseMoveEvent(event); // propogate to parent widget
printf("C\n");
}
Now it's printing BCBCBC... which is great, but I can't seem to nudge it up one more level...
Another edit: It was being propogated up properly, I just didn't have setMouseTracking enabled.
QGraphicsView::mouseMoveEvent(event);
Doesn't propagate up to the parent -- it actually propagates down to the scene.
Here is what's happens -- QGraphicsView receives QMouseEvent, translates it into QGraphicsSceneMouseEvent and passes it to the scene. Scene then passes it to appropriate item or, in your case, prints "B". Event handler then returns back to EditorView and prints "C".
Then, if you explicitly ignore event (mouse move is accepted by default), Qt event handler will pass the event to parent of EditorView. So try ignoring after you print "C".
Another thing about mouse move is this:
If mouse tracking is switched off, mouse move events only occur if a mouse button is pressed while the mouse is being moved. If mouse tracking is switched on, mouse move events occur even if no mouse button is pressed.
So make sure you have tracking enabled on parent of EditorView (or that you press buttons :)).
EDIT:
BTW, EditorScene is not a parent of EditorView. Well, it is in your code, but only in QObject meaning of parentship (memory management only).
QGraphicsScene and View don't have normal family relationship -- scene can have multiple views and those views are children of unrelated parents.
For window event propagation purposes you must have QWidget based parent. In fact, I'm pretty sure you reparent EditorView to EditorWindow, or one of its children (when you add it into layout).
INSTAEDIT:
For coordinates you want View itself to emit a signal. Both for decoupling reasons and because you probably want to show local coordinates of the view, and not of the parent window and not screen coordinates (right?). If you actually want scene coordinates, View is right choice too, because it knows transformation matrix.
Coordinates go like this:
Screen -> EditorWindow local -> EditorView local -> Scene transformed -> whatever item local transformed.
QGraphicsView::mousePressEvent( e ) in my mousePressEvent did the trick!