I'm developing a small Qt application similar to the DiagramScene example. I have subclassed QGraphicsView instead of QGraphicsScene. My view is zooming in and out with the mouseWheel, I can drag it with the mouse and I can add Nodes and Links with clicking.
I click on one Node, (the first end of the line item is set), then move the mouse (the second end of the line is following the mouse cursor), then I click on the second Node and anchor the second end of the line item to this second node.
The problem is, when the view is zoomed in, or I have moved the view, when I click on a Node and move the mouse, the preview of the link is not visible. When I click on the second Node - the link is still not visible. The link between the two Nodes becomes visible only after I zoom out or drag the view to some point and it intersects with the sides of the view.
Any ideas how to fix this?
Thank you so much in advance.
I finally fixed it. I was wrong to use data members for the coordinates (also the bounding rect and paint method) of my custom Graphics items. I changed the code using the setPos() function which gives the right coordinates to my items. #Merlin069 thank you, actually your last question got me thinking whether I set the coordinates correctly.
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In graphics view m setting scene in that adding objects (by dropping ), i can move these items by mouse, when i moved one object on another object moved object should be transparent. how can i make it?
I don't believe you actually want full transparency since it will make it impossible to visually recognize the transparent object later on. Reduced opacity - yes.
As for your question: each item inside your scene has a bounding rectangle (or other type of bounding area). You can easily get it by calling boundingRect() of your item. The returned QRectF has (just like QRect) has the bool QRect::intersects(const QRect &rectangle) const function, which takes another rectangle and checks if a collision is present.
Whenever you move your mouse while dragging an item you need to iterate either through all or just a subset of all items in your scene (by subset I mean just the items in a specific region to increase the performance) and check for collision. If a collision is detected, you can alter either the item you are dragging or the item underneath it.
Of course to make sure that one item covers another one you also need to check the Z value. The easiest way to do that is if you keep all currently not being dragged items at the same Z level and then, whenever you drag one, increase it's Z level by one so that it is "above" the others.
I am trying to make a simple program in which I have added a qgraphics scene and in this I have added a QGraphicsRectItem. I have implemented mouse press event, paint event, bounding rect. Now I have drawn a point on one side of rectangle because there can be multiple rectangle I can drop on screen so just to differentiate between them of different color. Now I can move my rectangle inside graphics seen and can increase the size of rectangle by moving it's one side at a time. The problem that I am facing is when I trying to draw point on one side of rectangle at the time of moving it, it leaves traces on graphics scene. can I remove the ghost lines?
This happens either because your boundingRect method isn't correct, or because you forgot to call prepareGeometryChange before making changes that affect the boundingRect result. Your boundingRect needs to include space for line widths, for example; that's a common mistake.
I have custom graphic item that draws some figure consisting of lines and polygons.
It has reimplemented method
hoverMoveEvent( QGraphicsSceneHoverEvent* event )
that indicates when need to highlight the figure (when mouse crosses the internal line or polygon ).
There are situations when items are drawn one above other, but hover event is accepted only by top item.
I tried to ignore event inside the method but it don't help.
To solve this problem need to reimplement method
QPainterPath QGraphicsItem::shape() const
in the custom item.
This shape should be exactly as a shape of "internal" painted items. Without empty spaces inside the bounding rectangle.
I have a QGraphicsRectItem over a scene. I intend to drag and drop this window over the scene. When the rect item reaches the left boundary end I have to show it appearing from the right end. Currently I am using two objects and hiding and showing them by calculating the boundary of scene which involves lot of calculations.
Is there any better way to achieve the same effect using just a single object?
Thank You
You could use a single item that spans the entire scene, and draw the rectangle (or 2 parts of it) in it's paint method.
But then you would lose the optimization of the BSP tree, your item would redraw even if some unrelated area repaints. If this is just 1 item, I guess it would not have much impact.
You would need to implement your own dragging with mousemove event and the like, though this is not much code, you just need to get it right.
I'm stuck on how to approach this. I have a QGraphicsItem within a scene, and I'm passing a hover event from the scene to this child. While the move event occurs (I'm just using mouseMoveEvent with mouse tracking on), I want another QGraphicsItem to follow the cursor.
I don't need any collision detection, drag and drop, etc. Just an item that follows the cursor. The only two ways I can think of are...
While the mouse moves, draw a new QGraphicsItem at the mouse position. I would need to clear the scene, redraw everything, and draw the new position on top.
Somehow use the animation framework and whenever the mouse moves, animate the QGraphicsItem to move to the new mouse position in 1 millisecond.
I'm probably either overthinking this or unaware of another way to do this... any suggestions?
I did it like this
Create the GraphicsItem cursor which will be moved with mouse-cursor, and store its pointer somewhere (in scene subclass for instance. I have a toolset, so for me it's in one of these tools)
Set its Z-Value (QGraphicsItem::setZValue) so that the cursor will be painted above all other items in your scene
Track QGraphicsScene::mouseMoveEvent events, forward these events down to the cursor pointer, and update item's position
that's it.
I guess it corresponds to your solution 1, except you don't have to clear the scene thanks to z-value feature.