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.
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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
I'm working on a small detection application using OpenCV and Qt.
my question is: what is the efficient way to mark the detected faces with rectangle knowing that I want this rectangles to be clickable in order to trigger some event for each clicked rectangle.
I've made this using a QPushButton ( with transparent background and some colored border) over a QLabel ( that contains the image ).
is there any other obvious way (maybe QSvg or QGraphicsView) ?
If you want to stick to widgets, then your current approach is the most obvious. If there can potentially be hundreds of faces, however, QGraphicsView would be more efficient, as it's designed for that.
If you can use Qt Quick, then using MouseArea and Rectangle within a Repeater would be the simplest approach. Exposing C++ code to QML is really simple, as well.
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.
Here is the thing, I have develop a manual Annotation Tool for annotating images, you know, use rectangles to mark parts of a human, head, torso, limbs, and store the information like width, height, center point, rotation. I use QT to develop this tiny tool, it's cool, but I face a problem. I want to save the pixels of the image which in a QGraphicsScene in the area of the rectangles (QGraphicsItems), so, I want to know how can I control the pixels of this area?
Thank you very much.
You can render the rectangle area into a QPainter which can be a QImage:
http://qt-project.org/doc/qt-4.8/qgraphicsscene.html#render
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.