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.
Related
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.
What I want to do:
In PySide, one could override the paintEvent() method of a QWidget to draw a custom widget. The bounding rect can be customized by overriding the boundingRect() method.
How does one do this in JavaFX? My goal is to create a custom Rectangle object, that draws itself smaller than it's bounding rect.
In context:
I'm creating an MS Paint clone in JavaFX. I'm working on the selection box that you use to select/move pixels around. I want the cursor to change to the appropriate resizing cursor when it is near the outside of the selection box.
However, the bounding rect is the same size as the selection box drawn on the screen, so the cursor only changes when it is on top of the box, but not when near. My solution is to set the bounding rect to larger than the actual selection box is, so the cursor change will occur. Then, override it's paintEvent() equivalent to draw a smaller selection box.
Thanks for your help.
I have a similar use case to you, and asked a similiar question here : Drawing transform independent layout bounds in JavaFX.
The JavaFX API is much higher level though than Java2D or PySide (I am assuming from your snippets, because I actually never heard of it ;) ), it does not allow you to override painting of Nodes, nor can you stop a Node from inheriting its parents transform.
This means that you need a seperate Group parallel to your content where you create the selection box and update it according to your needs (content changes etc.).
Example SceneGraph:
Scene
contentGroup
someShapeFromUser
selectionBoxGroup
selectionBoxOfSomeShapeFromUser
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.
I have a component which draws a grid of things and I want a small highlight square to follow the mouse around highlighting the square that the mouse is currently over.
The whole grid is basically just one big sprite (it's a very large grid and this was faster than using pre-existing components) and the highlight square is another sprite which I'm trying to move around according to the mouse position.
So, what I have is a MouseEvent.MOUSE_MOVE handler attached to the grid sprite and this tries to determine where the mouse is and what square it's over so that it can move the highlight square to the right place. I was using localX/localY for this, but as soon as I move the highlight sprite under the mouse, these become local to the highlight and not the grid!
I was toying with stageX/Y as well, but these seemed to become pretty useless when the stage is scrolled or your component is hiding in nested display containers.
Basically, i think, you want to check the the grid components mouseX and mouseY property which will give you the mouse coordinates relative to that component. Then a little bit of maths should be able to give you what grid element you are over.
Assuming your highlight sprite is a sibling to the grid and they are both children of the main application, and you've drawn child sprites (squares) within the grid: You could add event listeners to each of the grid's square sprites. On rollover, highlight the square. Then you probably won't need to perform any translation of grid or mouse coordinates using grid.localToGlobal(new Point(targetSquare.x, targetSquare.y)) or highlightSquare.globalToLocal(grid_point).