I am playing video using the Qgrpahicsscene, QgraphicsView, qvideowidget
videoWidget = new QVideoWidget;
QGraphicsScene *scene = new QGraphicsScene;
QGraphicsView *graphicsView = new QGraphicsView(scene);
scene->addWidget(videoWidget);
the video playing correctly, what i need is when i adjust brightness in videowidget it is not reflecting and i have checked the videowidget brightness level it is setting.
please share some ideas,
thanks in advance
Update the scene after the change of brightness. Like this:
videoWidget->setBrightness(bright);
scene->update(scene->sceneRect());
You can achieve pretty much all kinds of effects and corrections with the use of shaders, brightness in particular is a very simple fragment shader, just multiply each pixel's luminosity by a real multiplier. With QML you even have the ready to use shader effects as well as the QML video effects example.
Brightness/Contrast
All ready to use effects
QML video effects example
You could use shaders even with widgets if you go for a QGLWidget base widget and still get the great performance.
Related
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 making fractal creator software. So I need one scene per fractal and these scenes need to be "layered" because of zooming rubber band.
I've already tried to write it the "widget" way, so I had one custom widget called "canvas". In my canvas class I overrided paintEvent, and inside this event I rendered current fractal. Everytime when somebody clicked to menu with another fractal, I called update() method and new fractal was rendered. To zooming I used overriding of mouse events and update() of canvas. At the first time I repainted the whole canvas, but it was very very slow. After that I repainted only the part under the rubber band, but still slow when I'd like to select some bigger area and other problems with repainting.
So I've looked for another way to do it. Layers. I've found the QStackedWidget, but I didn't find way how to make visible both of my layers and the top one to be transparent. After that, I've found QGraphicsScene and this seems to be the best way to do it. But I don't know the correct procedure to do it. Below are two procedures I'm thinking about:
Create QGraphicsView
Instead of the widget, the canvas will be QGraphicsScene
I'll override some QGraphicsScene event (but I don't know which one - drawItems() is obsolete and override update() seems wrong to me, but maybe...)
When other fractal will be chosen, I'll repaint canvas by calling update() the same way as in my "widget" solution
In the foreground layer will be zooming rubber band
or:
Create QGraphicsView
Instead of the widget, the canvas will be QGraphicsScene
Every fractal will be the child of QGraphicsItem
When other fractal will be chosen, I'll remove the old one fractal
item and replace it by new one and probably call invalidate()
In the foreground layer will be zooming rubber band - I think, that
it's common behaviour of the QGraphicsScene isn't it?
Is one of my reasonings correct? Do you suggest anything else? Fractals are complicated in the calculations and It's very important to repaint only if it is necessary. Could you help me, please?
Thank you :-)
Edit: "zooming rubber band" explanation:
I'm sorry for my expression "zooming rubber band". It means scale (zoom) the area below the selection made by the rubber band - zooming the same way as in Photoshop CS5 (for example). And I'd like to know what part of the scene is repainted while selecting this way. If there is repainted whole scene, or the part of the scene below selected area, or there is nothing repainted and rubber band selection is done in separate layer.
I hope my explanation helped :-).
In Qt, a QGraphicsScene can be thought of as a world of items, with a QGraphicsView as a window into that world. Therefore, you should be adding items to the QGraphicsScene, based on QGraphicsItem (or QGraphicsObject if you want signals and slots).
In your situation, I'd create a Fractal class that inherits from QGraphicsItem and add that to the scene. Ensure to override the necessary pure virtual functions such as boundingRect and paint.
Do not calculate the fractal code in the paint function. I suggest the Fractal class stores a QPixmap (or QImage if you're drawing at the pixel level) and render the fractal to this. Then perodically, in the paint function, the Fractal class would render the contents of the QPixmap with a call to painter->drawImage or painter->drawPixmap; whichever is relevant in this case.
As for zooming, your Fractal class can then response to being scaled, appropriately changing the rendering on the internal representation.
I'm working on an application that is using map tiles in a QGraphicsItemGroup to render a map and I want to make the switch to OpenGL so I can add 3D shapes on the map.
In order to do so as smoothly as possible I would need to get a texture from this QGraphicsItemGroup.
In case anyone has this issue I managed to get something I could work with. Rather than using the QGraphicsItemGroup I took the whole scene and made an image from it that I use as a texture.
Code extract : (map is my QGraphicsScene)
QImage img(ui->map->width(), ui->map->height(),QImage::Format_ARGB32_Premultiplied);
QPainter p(&img);
ui->map->fitInView(0,0,scene.width(),scene.height(),Qt::IgnoreAspectRatio);
ui->map->viewport()->render(&p);
p.end();
img.save("tmp.png");
I'm starting using Qt in my application. My application is MFC based. I want to draw some QGraphicsItems in my currect MFC view, is it possible?
You may say that it could be done by hosting QGraphicsView with QWinWidget in the MFC view, that don't work, however. Because my Canvas (MFC view) supports zooming and rotating while the QGraphicsView itself don't. When I zooming the QGraphicsItem, the QGraphicsView shows scroll bar instead of enlarging itself.
Any suggestion? Thanks!
Theoretically you could use QGraphicsScene::paint to paint the scene with your QGraphicsItems in the buffer, and then draw it to MFC view, but it does not make any sense...
What is the problem with QGraphicsView anyway? Have you taken a look at the rotate(), scale(), translate() or shear() functions of it?
You can turn off the displaying of scroll bard of QGraphicsView by setting the ScrollBarPolcies to Qt::ScrollBarAlwaysOff. (QGraphicsView is a sub-class of QAbstractScrollArea.)
I am not sure I understand what you mean by rotating QGraphicsView itself instead of the content. Without the scroll bars, I don't see the difference. Also much of the functionality of QGraphicsItem like editing as you indicated, depends on event handling in QGraphicsScene and QGraphicsView to work. I don't think plugging just a QGraphicsItem into the MFC view will do what you want.
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.