I am trying to implement a selection box in Qt:
When the user holds down LMB and drags, a rectangle is created and drawn real time to the screen. I also want to be able to select on only one dimension.
I think overriding the methods QWidget::dragEnterEvent(QDragEnterEvent*), QWidget::dropEvent(QDropEvent*) may help, but I don't know how to dynamically obtain and draw the rect.
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I am using QPainter in Qt 5.9 using C++ to make a plot and update it based on mouse events.
I would like to know how to plot an error bar that is something like this:
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Of course the gaps shouldn't be there between the vertical and horizontal lines.
I need to be able to drag the error bar around on the plot and obtain the co-ordiantes of the center position of the error bar when the mouse button is released. So far I have made a plot with axes and labels. Not sure how to get the error bar using QPainter or any other Qt lib class.
Please provide some insight on how make/plot the error bars. Is there a simple way to do that in QPainter ?
If you are using QPainter you should implement drag-n-drop yourself. It's not that difficult if you don't have too many objects on your plot.
Here's the basic idea:
First of all render all objects. Than you need to reimplement mousePressEvent and mouseMoveEvent in your plot widget. In mousePressEvent you should check if you've clicked on the draggable object and define this object as currently being dragged. In mouseMoveEvent just move this object (if there is one) by changing its coordinates and rerender plot.
You will probably want to optimize plotting to avoid full plot rerender at each mouse move tick. This can be achieved by plotting rarely changing objects to QPixmap/QImage, than rendering this QPixmap/QImage on widget and than plotting error bars and all other kinds of objects that could change at each mouse move tick over this pixmap. At each repaint you will need to define if you need to replot just error bars (or some other dynamic objects) or all widget. I personally implement this by defining bool needFullRepaint which is set to false by widget after each render tick and is set to true after some data inside widget changed.
This is kinda low-level approach, it will require high level of skill and some time to be spend but you will be awarded with maximum control of the rendering and interactions with the widget, which is not always possible with the QGraphicsScene or QCharts
It's going to be a fairly involved project for someone who hasn't used Qt before.
You will want to use QGraphicsScene in all likelihood, rather than a QPainter example. QGraphicsScenes are way easier than QPainter for interactive examples.
Use QCharts as a starting point, they have examples for how to plot data and then move items as a result. Check out the callout example, in particular, which has you paint a callout labeling the position of the cursor on the graph.
Look at the "Drag and Drop Robot" example from Qt.
All of these are an excellent starting point for how to implement draggable features to create an interactive plot. Qt makes it easy for a generalized sense: however, for many plotting features (at least until QtCharts), Qt was much more difficult than specialized plotting libraries.
How can I create a triangular pushbutton in Qt? What is the most simplest way of executing this? I use the designer to create buttons and not code.
Also, I read somewhere that shapes may be changed as long as the frame of the button is still rectangular but I want the frame to adjust according to the shape as well. How can I achieve this?
More detail: I want to place lots of small triangular buttons next to each other with every other triangle flipped. Each triangle button has it's own function, etc (no overlapping borders accepted). Can anyone give me a descriptive explanation for how I might go about this?
The geometry on a QWidget is always a rectangle.
It would be possible to create a QPushButton derivative, override its paintevent and do some nasty painting considering its neighborhood etc. but it would be really a pain...
it is much easier to use a QGraphicsView, QGraphicsScene and add appropriate QGraphicsItem (maybe the QGraphicsPolygonItem?), add them and use their signals/slots or create a derived class for your purposes.
It is not that hard to override the mouseevents to recognize clicks and you can even use the QStyleSheets to let the "button" look like it gets pressed.
I have a list control. I want to draw selection rectangle on my own.
For example: when i clicked on an item it will draw an selection ractangle on that item and the item is next to it (or can be somewhere else).
Can anybody tell me how to do that ?
Thank you!
To draw a focus rectangle, call the DrawFocusRect function. To enable Visual Styles, call the DrawThemeBackground function (Parts and States: LBCP_ITEM and LBPSI_SELECTED).
Either way, you will have to create an owner-drawn List Box to be able to adjust rendering. For an MFC CListBox control you have to override at least CListBox::DrawItem (and usually also CListBox::MeasureItem).
Could somebody tell me how to erase a rectangle that has just been drawn on an image?
In the application, I have an image displayed on a document (MDI application). The user can select a portion of the image. I implemented this feature as letting the user start the selection with a CRectTrackerColor (derived from CRectTracker) object. The selection works fine: a user is able select a rectangle using the mouse. A rubber band rectangle is shown as a feedback. After the user releases the left mouse, the rectangle is colored based on my pen color. Then I present a dialog for OK/Cancel. Upon Cancel, I would like the rectangle to disappear. How should I go about doing that?
Thanks.
Just invalidate that rectangle so it'll get redrawn normally.
Let's say that I have an application frame, and I want to show a popup QCalendarWidget over on the right side of the frame. Normally, QT will clip the edges of the QCalendarWidget, cutting it in half and not displaying the rest, as it would be over the right side border.
Is there a way to work around this limitation without resorting to implementing a QDialog?
I want the widget to be visible outside the bounds of it's container.
If you'd show your Calendar, let's say, after a button click, as QDateTimeEditor does, it's contents will not be clipped, cause it do not belong to frame. It will be just a widget, that shows in a dialog manner. And maybe you should even place it in QDialog, that is modal and provides some convenience methods, rather then simple QWidget.
Btw, why don't you want to use QDatetimeEditor?