I'm trying to add better UI for an OpenGL-based program with Qt. Since I can modify that program it's not hard to get the window ID. So I think embedding it into a QWidget would be a good idea. However, it doesn't work like I expected:
After XReparentWindow is called, the OpenGL window lose its decoration, but the position didn't change.
If I use XConfigureWindow to move it to position (0, 0) relative to parent it goes to the top-left corner of the screen, but not the QWidget.
After reparenting, a third window can cover the QWidget, but nothing can cover the OpenGL window.
X11 reported no errors during the whole operation.
It seems the parent of the OpenGL window has been set to the root window instead of my QWidget. What should I do to make it work correctly?
You can replace your current OpenGL window with a QGLWidget which provides an OpenGL context and can be placed into a Qt window directly.
I'm not sure Qt supports XReparentWindow calls like that. The docs don't seem to say it does, so it's probably a bad idea to use it. You could try QWidget::create() instead.
Related
The basic idea is: I would like to draw over everything on the screen.
One way I can imagine this is creating a transparent full-screen window without window controls (minimise, maximise, etc.) or borders. Then drawing into that window which is transparent. The problem I can think of is that I will be unable to control windows which are behind our transparent window.
How could I do something similar to this, without the mentioned problem? I would also like it to work on multiple operating systems if possible.
Edit:
The user will not be drawing with the mouse or other means on the screen, but will be able to continue use his desktop like normal, without that my program interferes in any way (other than the drawing on the screen). My program will only display something on the screen, which the user will be unable to interact with (at least that's the plan).
Qt 5 implements it:
QWidget w;
w.setWindowFlags(Qt::WindowTransparentForInput);
Qt 4 didn't support this functionality yet - see QTBUG-13559. The bug report had a hint on what needed to be done for Windows.
The method you describe is the one to use; a transparent full-screen window.
If you're using the left mouse button to draw, you'll need a mechanism of switching modes to be able to select items through the window and send events to the operating system.
[qt 4.8]
To get correct window dimensions including its frame, I do the following (as described e.g. here, see comment from Daniel Hedberg).
mainWindow.move(-50000, -50000);
mainWindow.show();
// do something with the window dimensions
mainWindow.move(0, 0);
mainWindow.show()
This works fine, however, I have a problem with the move(0,0) call: It makes the window always appear at position (0,0), while I would like to have the default behaviour, this is, the application only suggests to the window manager that (0,0) is a good place to position the window, and the WM might decide to shift it if necessary to avoid overlapping. In other words, I would like to switch back to Qt's default behaviour as if there weren't a call to move at all.
How can I do that?
One solution is to store Windows original position and use that. For extra safety (in case screen resolution changes), check that entire window still fits on screen and move and even resize if it does not.
A hacky alternative would be to create and open empty, possibly transparent dummy window of the same size and see where it gets positioned. Then move the original there and close the dummy one. Reading your question carefully, I think this would do what you are after.
I don't know of a Qt way to ask Window Manager to reposition the window, so if you really need that, specify the OS etc details.
Looking into the source code of Qt, I can now partially answer my own question: To convert a call to move into a suggestion for positioning instead of a request, do this:
mainWindow.move(100, 100);
mainWindow.setAttribute(Qt::WA_Moved, false);
mainWindow.show();
I've tested the code under X11 using Qt 4.8.4, and hopefully it works with on other platforms too.
Unfortunately, this doesn't solve the very problem I have, namely to use show to get the (decorated) dimensions of an off-screen window which then gets moved to the screen, calling show again. It seems that the first call to show directly sets platform-specific window manager flags which aren't completely reset and reevaluated in the second call. Actually, I'm going to think that this is a bug in Qt, so I'll report it accordingly.
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.
Is it possible to cut a QGLWidget? I mean I would like to cut it so i get access to the gui below. It sounds strange, but it would be a lot of work for me to divide my QGLWidget into two. I hope you understand what I mean.
I don't fully understand what you mean by "cut" and GUI below. In Qt with layout mechanisms properly used a widget consumes the area it covers and there are no widgets beneath it.
Do you want to render multiple views into a single QGLWidget? This is easily achieved by proper use of glViewport + glScissor.
EDIT due to comment
There are two kinds of windows:
Top level (those you can freely move around on the screen)
Child windows (subwindows like widgets or panes in a top level window)
Child windows again come in two characteristics:
logical child
real child
A logical child window just consists of its position, dimension and layer and are managed by the toolkit. From the view of the operating system there's just one top level window. The toolkit is it that manages its internal state to give the impression of independent sibling windows in the toplevel window.
A real child window is manages by the operating/graphics system. Such real child windows may share their graphics context with their parent and sibling. However OpenGL only works well if the window into which a OpenGL context is created has its very own graphics context. Thus any OpenGL child window inevitably will have its very own graphics context and graphics system window object. Most graphics systems out there don't properly support applying shapes onto child windows (only toplevel windows, and then this also conflicts with OpenGL).
So this boils all down that it's virtually impossible, nor advisible to try to "layer" an OpenGL window on top of a sibling. It may work in some circumstances, but most of the time it won't.
That's the bad news.
The good news are, that you simply looked in a slightly wrong direction. I hereby direct your view towards QGraphicsView. QGraphicsView supports OpenGL as a backend, you can also write your own OpenGL renderer code to be executed within a QGraphicsView. But furthermore QGraphicsView can also be used for rendering widgets, also using OpenGL. So all you have to do is putting both your OpenGL rendering code and your widget into a common QGraphicsView scene and are done. And here is a tutorial http://www.crossplatform.ru/node/612 the result of the tutorial looks like this:
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.