transparent QLabel with a pixmap - qt

I have a QLabel, and I put an image on it using setpixmap(). That image has alpha channel.
The QLabel is on a QWidget which has a border-image specified by an image (so that the image is rescaled to fill the QWidget).
On the transparent parts of the QLabel, the result is not the image specified on the QWidget, but a gray color characteristic of "no color" Widget.
My question is how do I make this in such a way that the transparent part of the QLabel shows the border-image of the QWidget?
I've tried canceling autofillbackground, changing the background color of the QLabel to white transparent, but none helped.

You need to set the Widget Attributes and Window Flags appropriately:
Using QWidget::setAttribute() and Qt::WidgetAttribute...
Qt::WA_TranslucentBackground needs to be set to true.
Along with learning the Window Flags Example should help a lot.
If you are just looking for a single widget that paints a frameless image...
Here is a perfect example:
QSplashScreen Replacement

Related

Qt Window with transparent background image

I placed background image like this:
setWindowFlags(Qt::FramelessWindowHint);
QPixmap slika("some_image.png");
QPalette paleta;
paleta.setBrush(this->backgroundRole(), QBrush(slika));
this->setPalette(paleta);
If I make this picture transparent, when application loads, it will only blink and disappear. But if I make this image with no transparency, then everything is ok. Why Qt refuses to use transparent image?
I don't know what is your use case for this, but you can also try using setStyleSheet method to make background transparent.
setStyleSheet("background:transparent;");
setAttribute(Qt::WA_TranslucentBackground);
setWindowFlags(Qt::FramelessWindowHint);
Hope this helps.

Qt 4.7.4 - Make transparent pixels clickable (expand hitbox) in QGraphicsItem pixmap

I am creating a circuit schematic editor using Qt Creator. I have a QGraphicsScene/QGraphicsView canvas that I would like to drop images of circuit components onto and move them around.
I am currently using a pixmap QGraphicsItem and adding it to the canvas and making it movable. This works great when you click directly on the symbol's lines, however the symbol does not move when the transparent areas in the image are clicked.
Is there a way to expand the hitbox/mouse area to make these transparent regions respond the same as the other regions do on the symbol? Below is how I am adding the image. (I need the image transparent so that other symbols are visible behind/infront of it)
QGraphicsItem* b = canvas.addPixmap(QPixmap(":/images/ground2.gif"));
b->setFlag(QGraphicsItem::ItemIsMovable);
b->setPos(qrand()%int(canvas.width()),qrand()%int(canvas.height()));
All help is much appreciated! Thanks!
Josh
You can call QGraphicsPixmapItem::setShapeMode( QGraphicsPixmapItem::BoundingRectShape ) to have the item treated a rectangle.

Semi-transparent QWidget over QGLWidget: Strange results

I have a full size QGLWidget which paints the application background using QPainter (might change to native openGL commands in the future).
On top of this QGLWidget I use QWidgets (non-GL) for the user interface elements. These are, for example, QLineEdits and QPushButtons. I put them into a custom painted QWidget which uses semi-transparent background painting. The paintEvents of the QLineEdit and QPushButton are overwritten and use semi-transparent backgrounds, too.
The whole UI should look like the following (This is a screenshot where I disabled OpenGL and used QWidget instead of QGLWidget for the background. Note the semi-transparent top bar which also draws a shadow (within its own region)):
When the QLineEdit has the focus, it should have a higher opacity but still not fully opaque:
So now, with OpenGL enabled (The background then is a QGLWidget), the semi-transparent widgets above don't paint on top of the background but on (it seems to be) uninitialized data. The image shining through the top bar is sometimes the whole window itself and sometimes other windows currently being on my desktop.
This currently looks like the following (In this screenshot, the data on which the semi-transparent painting operations are painted on seems to be an image of the widget itself, having an offset.):
When I wrote text into the line edit (here: "This is some text which has been there before!"), removed it and set the focus back to the background widget (so the magnifier icon and the placeholder text appear), the previously painted things still shine through (Note that the visible border should not be visible anymore, but also still shines through):
So the problem is: Instead of being painted on top of the underlying widgets, the semi-transparent widget is painted on top of the old results, initially being something like "uninitialized memory".
Why does this happen? How can I solve the problem?
Things you should know before answering:
The background scene is a composition of tiles which are rendered off-screen. So it can be painted very fast and repainting of the background for every little change of the overlay isn't problematic.
The top bar is a custom QWidget with manual painting and arrangement of the contained two widgets (the button and line edit).
The two widgets overwrite the paintEvent, only draw their own (semi-transparent) background when they have focus and don't use frames already provided by Qt. So the white border in the second screenshot is drawn in my custom paintEvent.
I want the background and the composition of overlay widgets to be separately implementable. The background is an AbstractMapView which has some concrete map view classes. The whole window is an AbstractView (there are multiple concrete views, too), which contains both a concrete map view and the overlay widgets, composed in a way itself decides. Therefore, I don't want the logic of the overlay widgets to be part of the underlying map view. (I hope you understood this, as it is a bit complicated.)
This sounds like an issue where the GL content (i.e. your background aka the QGLWidget) is not in the Qt context. While I'm not a pro on GL painting with Qt, you may want to look at this discussion regarding GL painting and a QLabel for some direction/potential hints.
http://www.qtcentre.org/threads/40335-QLabel-on-top-of-a-QGLWidget-background-issue
In short, we here at the office use OpenGL painting and offscreen rendering of maps and it's very important to make sure Qt is aware of the pixels so your foreground widgets can have the semi-transparency applied to their backgrounds.
The particular product we use also renders the map in tiles and supports providing the GL output in a buffer (i.e. it's call a snapshot and is provided as a bitmap) at which point we use the paintEvent of a regular QWidget to paint the buffer so that the painted pixels are in Qt context.
You can define a Qframe with Qt::SplashScreen flag as the search box and set its opacity. Put your widgets inside it such as the search textbox and positon it where it should appear on the mainwindow. It will also be a good idea to reposition it as the mainwindow is moved or resized overriding its moveEvent.

How to make Widgets background transparent in Qt

I am building an App in which I had given background to my mainWindow only and all other widgets are used without any background, but when I run the app they are not 100% transparent they are somewhat translucent, is there any way to make them 100 % transparent so that only foreground can appear with no background hint.
Could you post the code you are using to get transparancy at the moment? If you say that you get "something translucent" I think that you created a tool window which is not what you really want.
A really transparent main window could be achieved by removing the title bar (give the QWidget constructor Qt::FramelessWindowHint as second parameter - WindowFlags), draw everything in the widget that should be transparent in a uncommon color (like 255,0,255) and then cut it off.
A very primitive example of cutting off parts of a QWidget:
QBitmap b(100, 100);
b.fill(Qt::black);
setMask(b);
QBitmap must be black on that pixels that shall be visible and white on that are not. In this example just the 100,100 area starting at 0,0 will be visible, the rest of your window will be invisible.

QT Transparent Layout

I am using a vertical layout (QVBoxLayout) to manage buttons. I would like to make its background color as 50% black transparent. Is it possible ?
sw
Depending where you want the border of the transparent area, you will need to group the buttons in a widget (as SigTerm said) and then you can assign a color either via the palette
QPalette palette = widget->palette();
palette.setColor(QPalette::Window, QColor(100,100,100,100));
widget->setPalette(palette);
or use a stylesheet
widget->setStylesheet("QWidget{background-color: rgba(100,100,100,100);}";
the stylesheet has the advantage that you can style all of your application from one spot that is not in the code and set an application wide stylesheet via QApplication::setStylesheet(QString)
Ahem... it's been a while since I used Qt, but as far as I know, QVBoxLayout has no background color, so no, it isn't possible. Layout isn't a widget and it isn't being painted at all, it only manages child widget sizes.
If you want to create colored layout, you'll probably have to create a widget with whatever color your want, and then parent QVBoxLayout to that widget.
It'll become more fun if you want color of all layout's children to be affected by color of QVBoxLayout's parent, but I think that "Embedded Dialogs" demo from Qt4 demo may give you an idea about how it can be done.

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