Solved Exact correct size needed
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Hi, I just found that I use to call "showMaximized" on "main.cpp" instead of "show" to make the application full screen.
I've tested with calling "show" and yes, it does not fit the item to the view the first time.I don't like too much this solution but you can use this
QTimer::singleShot(50, this, SLOT(fit()));
Define "fit" method as slot.
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@ollarch
Thanks, it sounds like (if I understand correctly) you are saying you find the same issue as me first time? Though I haven't seen this commented on elsewhere.As I said earlier, I have no problem with rectifying via your
QTimer
, but since I have rectified viashowEvent()
(as per my code) why are you not satisfied with that approach. any reason?I have moved on now to mouseworks, and am happy with my coordinates :)
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As I said earlier, I have no problem with rectifying via your QTimer, but since I have rectified via showEvent() (as per my code) why are you not satisfied with that approach. any reason?
No, I have any problem and I'm satisfied that it works.
I have moved on now to mouseworks, and am happy with my coordinates :)
Now you can try to rotate the view 45 degrees and you will see that when you map the view coordinates to scene coordinates you still have the correct pixel coordinate.
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@ollarch
Indeed, though rotation is not something I will want to do, but I take your point.Overall I am very happy with the approach you stuck with and made me adopt for my situation. As I said, I thought I was going to have to do my own coordinate transformation arithmetic taking into account my current scale/zoom setting etc. I am much happier that all I have to do is call Qt's already-written
mapToScene()
to do it for me, and everything makes logical, "purist" sense to me.So thank you for sticking to your guns and recommending the approach I was really looking for!
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Thanks for the clarification. mobdro
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Overall I am very happy with the approach you stuck with and made me adopt for my situation. As I said, I thought I was going to have to do my own coordinate transformation arithmetic taking into account my current scale/zoom setting etc. I am much happier that all I have to do is call Qt's already-written
mapToScene()
to do it for me, and everything makes logical, "purist" sense to me.I'd rather not reinvent the wheel.
So thank you for sticking to your guns and recommending the approach I was really looking for!
I'm happy. ;)
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@ollarch
Hi @ollarch , hope you're around and see this question (or anyone else who knows!)....I am moving onto my requirement to draw a shape on the view to follow the mouse. It will be see-through but with a frame, so that user can see where on map the mouse is.
For now I will do that via a
QAbstractGraphicsShapeItem
on theQGrapcicsScene
, because that's the only way I know how to do it; plus it will use scene coordinates, which is easy.However, I am aware this is not "correct". There should be no permanent object on the scene for this. And, for example, although I do not have multiple views onto the scene, if I did it would show up in all views. Which is not correct. This shape is a temporary object which belongs/should be shown only in the view where the mouse is moved, not on the scene shared across views.
The "correct" thing to is to draw this on the
GraphicsView
only (with necessary coordinate calculations, but that's not the point). I came acrossQRubberBand
which looks like the sort of thing which should be used (and I think that can be put on the view only). But unfortunately for me that only allows a line or a rectangle, and I will want a circle or a hexagon for my usage.So.... what is the right way to do this, please? :)
EDIT
I have now come across, say, https://www.qtcentre.org/threads/4479-Adding-Rectangular-overlay-on-graphics-view [from 2006!], which is asking just my kind of question:To simplify my problem, lets assume that we have two different graphics views. Both of these views have the same scene applied to it. When the user clicks on a specific point in the first graphics view I want to draw a rectangle related to the point she clicked, but I want it to only be visible in that graphics view.
I think this ends up saying to use QGraphicsView::drawForeground(QPainter *painter, const QRectF &rect) to achieve this. Is that the route I should be following? [And if it is I shall have further questions! Because the principle there is not good enough as-is for following the mouse and redrawing when it moves.]
UPDATE
Now that I am beginning to understand what facilities the graphics scene/view offer. I am now sailing along, using the foreground layer of the view viaQGraphicsView::drawForeground()
to draw my mouse-follow-shape, callingscene()->invalidate(QRectF(), QGraphicsScene::ForegroundLayer);
to cause it to redraw frommouseMoveEvent()
. I think I have got this right!Which now makes me think: maybe I should be drawing the map on which all this happens via
QGraphicsScene::drawBackground()
instead of in aQGraphicsPixmapItem()
on the scene? For one thing, I believe the scene's background layer is cached for speed by default, which sounds good for an unchanging map background? -
So you want to display a rect only on the first view? You could create two scenes and two views and add only the rect into the first one. If the second view is some kind of "only selected view" you can take the rect position and size to crop the image and set it to the QGraphicsPixmapItem on the second scene.
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@ollarch said in Exact correct size needed:
Hi @ollarch. Your post has just crossed with the latest UPDATE I have typed into my post above!So you want to display a rect only on the first view? You could create two scenes and two views and add only the rect into the first one.
Nooo, I don't think so! 2 scenes?! Just for a shape on a view?
I'm pretty sure now that I understand a bit more that what I am doing via
QGraphicsView::drawForeground()
is the correct, cheapest way to draw a temporary foreground shape --- which is not an object on the scene --- to follow the mouse.You can see there that I am getting so excited now that I understand layers --- background -> any graphics objects -> foreground --- plus the fact that
QGraphicsView
draws its own layers, QGraphicsView::drawForegroundReimplement this function to provide a custom foreground for this view.
The default implementation fills rect using the view's foregroundBrush. If no such brush is defined (the default), the scene's
drawForeground()
function is called instead.So I now think I ought best move the map pixmap out from being a graphics object and into the scene's background layer instead. I am enjoying this as I begin to understand :)
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If I understand it. When the mouse enters the view you want to display a rect (or circle) centered to the mouse position?
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@ollarch
Yes. (Only a touch more complex than that: it has to map to nearest rect/circle/shape where the map is notionally divided into a grid of distinctly-located shapes, rather than continuous, and "snap" to there. But that is a detail.) And this shape must only be drawn on the view where the mouse is being moved; it does not belong to the scene, and if there were multiple views it must not appear in views other than the one with the mouse move. That's why it has to be view-based, not scene-based.But I am already at this point now, I have achieved what I need, using
QGraphicsView::drawForeground()
:) -
Hi,
Do you have a second view, for what?
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@ollarch
As I wrote earlier, presently I do not, but there is no reason I should not introduce one at a later date. One could have multiple views onto the same scene, so that user could see different areas of map in different windows (views) if desired.At which point I would only want the foreground shape following the user's mouse to appear in the one view where he is currently moving the mouse, not any other views (even if they happened to observe the same area of the scene as the current mouse view window).
This is why the shape should be drawn in
QGraphicsView::drawForeground()
, which is local to one view, not either inQGraphicsScene::drawForeground()
nor via placing aQGraphicsItem
on the scene (both of these would show the shape in all views observing that area of the scene, which I do not want.)As I say, I have this working well now :)
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I was only thinking on a another way to to this.
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@ollarch
:) No problem. You have really helpful getting me going on gfx scene + view.I am finding that
QGraphicsView::drawForeground()
is the best way to draw a temporary shape on (the top of) the given view (only). I came across that somewhere (but can't remember where) as the suggested way to achieve this best. -
Happy to help.
;D -
This post is deleted! -
Think on a CAD software. The schematic have to keep the units regardless of the zoom applied or the rotation of the view. You can rotate the view, zoom it, ... but when you ask the view to map the mouse position into scene coordinates, this coordinates will still be the same pixel position.