I have video analysis c++ code and porting to the QT Creator for gui requirements.
We are detecting certain shapes and items from the video stream and adjust their size ie 100x100 and want to display on the screen. We can display through Label but only one QpixMap item.
What is the best way to show detected images automatically on a widget such as last 20 one that autosized?
Is there any a small code sample to start with it to show us the direction?
Thanks.
You could subclass QWidget and reimplement paintEvent to paint whatever you need using QPainter.
See Basic Drawing Example for details:
http://doc.qt.io/qt-5/qtwidgets-painting-basicdrawing-example.html
Related
I am making an app using Qt (currently 4.8) which displays a literal map from a large number of QGraphicsScene items. I would like to annotate the view with a scale. My requirement for the scale is that it is permanently fixed w.r.t the viewport widget. It needs to be updated whenever the view scale changes (zoom in, etc). There are other possible overlay items as well (compass, etc) so I'd prefer a generic solution.
I have looked at earlier questions around this which suggest:
using the ItemIgnoresTransform
using an overlay pixmap.
I tried IgnoresTransform but that way didn't work right: I couldn't figure out how to fix it in place in (say) the bottom corner of the viewport and was having some difficulty getting the text and lines always displaying in the correct size.
I scrapped that and subclassed QGraphicsView, adding an overlay pixmap by reimplementing the paintEvent (calls original one, then paints the overlay pixmap on top), and an alignment option to indicate where it goes. Coding some pixmap paint code produces a usable scale on the view. Yay! ... but it doesn't work with scrolls - I get "shattered" renderings of the scale all over, or sometimes no scale at all. I think this is because QGraphicsView::scrollViewportBy() uses viewport()->scroll() so I wondered if switching to ViewportSmartUpdate would help, but it doesn't help enough. I'd prefer not to switch to ViewportFullUpdate as that would likely slow the app down too much (there are millions of items in the scene and that would require a full repaint just to move around).
So. Any ideas from here? Would adapting my pixmap code to write to a new mostly-transparent Widget that is overlaid on the viewport be a better way?
Thanks for any help...
Though it may not be the best way of doing this, in the past I've added custom widgets to the window that holds the QGraphicsView / QGraphicsScene, which have the same graphic style as the QGraphicObjects in the scene. When the view is then used to move objects in the scene, or the scene itself, the items on the window remain in the same place.
Hope that helps.
I simply want to paint a 1 pixel dot on a specific point on the screen. Is there anyway to do that? In QML or cpp?
Rectangle QML item should works good for you: http://qt-project.org/doc/qt-4.8/qml-rectangle.html
If you need to draw something more specific and more flexible, then you can customize QDeclarativeItem in C++, unset QGraphicsItem::ItemHasNoContents flag in your custom class and implement paint method. More details: http://qt-project.org/doc/qt-4.8/qdeclarativeitem.html
I would like to create a simple effect with my qt gui, but i have no idea how to achieve this.
I have several widgets, that i implemented as subclasses of qwidget. These are part of another widget and live in a layout. When the mouse hovers over these widgets, i want them to appear bigger to highlight the selected one.
This is what i already tried:
Override the paint event, and simply paint it bigger. But then, the other widgets that also live in the same layout overpaint the oversized areas.
I also tried to call the paint function "by hand" from the parent window, to get control over the painting order. But that didnt help either.
I think there has to be a possibility achieving this effect this qt, but i simply dont know how.
Any ideas?
You could either:
create your GUI inside a QGraphicsView, with QGraphicsWidgets and use setScale when the mouse enters or leave the widget, or
use QML.
I am building a game using QT in c++. I have extended the QWidget class as a painting surface and have set up a thread to refresh the screen. What I need now is to load the sprite sheets from file, break them up into separate 64x64 pixel images, and then paint them to the screen. Does anyone have some advice for how I should go about doing this?
TIA
Some QPainter::drawPixmap() variants has the option to specify the rectangle in the pixmap to be drawn. This will help you keeping the sprite sheets without breaking them up into small images.
For repeated sprites, QPainter::drawPixmapFragments() probably will have better performance and also allow sub-image drawing.
I'm writing a simulation of an embedded device's screen (which contains custom widgets on top of a main QWidget), and while the native size of the screen is 800x600, I want to be able to scale it up and down by dragging the window's corner. Without diddling with grid layouts and stretchers (which won't scale the fonts up/down), how do I accomplish this sort-of zoom? I think part of the solution might be to create a QTransform and somehow inject that into the QWidget for the entire application, or its QPaintDevice or QPaintEngine. I'd like to do this without putting QTransform in each custom widget, just the "main window" QWidget.
This is possible if you are using QGraphicsView as your main display widget. QGraphicsScene now supports widgets as content, so you can literally just scale them.
I believe the alternative is to reimplement the paint() for each widget, and manually set the transform/scale before the painting of child widgets.
Bit of a guess here as I've not tried it... but you could try putting the top-level widget into a QGraphicsView then get the QGraphicsView to do the scaling.
You could then enable OpenGL on the QGraphicsView and have it scaled in hardware so it's nice and fast.