I would like to add a keystroke handler to my Linux system (actually Ubuntu Linux, but pointers to X11 generally will be helpful).
The goal is simple enough in principle, I have a "drawing" program that lets me write on a transparent panel. I want to have a single keystroke that toggles this from the top to the bottom (and back again) of the window stack.
I guess I need to interact with the window manager, but that's where my ideas run out. Any suggestions for research directions?
Thanks,
Toby
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On an embedded system, due to very specific hardware/software limitations, we need another program to be able to display info via the framebuffer (/dev/fb0), while keeping our Qt5/QML program running in the background. We display a custom QQuickItem derived black rectangle (with nothing but a 'return' in the update()) in QML while the second program runs, but we still see flickering on our LCD display. We surmise that QT is still painting the Screen Graph (possibly of other items layered beneath the rectangle) to /dev/fb0, thus causing flickering by both programs writing to /dev/fb0 at the same time.We cannot use a second framebuffer approach (/dev/fb1) because the compositing increases processor loads dramatically such that the system becomes unusable. One thought is iterate through screen graph tree, marking all nodes 'ItemHasContents' flag as false so the screen graph renderer will not write to FB, then re-enable when the secondary program finishes its task. Another thought is to turn off rendering via the top level QWindow, but nothing in the documentation says this is even possible... Is this possible via QT, or even though a shell script?
/dev/fb0 sounds like you'd be working on a Linux-based system.
You're not saying whether you need the Qt application really continuing to run, just without screen updates, or whether simply "freezing" it while your other app uses the frame buffer would suffice.
If you are fine with the latter, the easiest solution to stop the Qt app from rendering is simply send it a SIGSTOP signal, it will freeze and cease to upgrade the frame buffer. Once you're done with the fb, send a SIGCONT signal. Sometimes the simplest approaches are the best...
I have written a small app that draws directly on /dev/fb0. I run it in a console-only environment without X-server. The problem I have is that once the app exits, the framebuffer stays the way it left it. Is it possible to make the terminal redraw all it's contents to refresh the screen after the app exits?
What I would do(if it does not depend on design and conceptual requirements) is to issue execve(clear).
Perhaps even execve(reset) would help. But for the latter i do not guarantee. First will surely do the job.
What I'm trying to accomplish is to have a process running in background from a Linux terminal which takes user input and does things according to that input even if the terminal window is not focused, so I can work with other GUI applications, and then when I push some pre-defined buttons, something might alter the program's state without loosing the focus of my current window. Just as simple as that (not that simple for me though).
I don't ask for an specific kind of implementation. I'm fine with anything that may work: C, C++, Java, Linux Bash script... The only requisite is that it works under Linux.
Thank you very much
Well you can have your server read a FIFO or a unix domain socket (or even a message queue). Then write a client that takes command line input and writes it to the pipe/queue from some other terminal session. With FIFOs you can just echo input from the command line itself to the pipe but FIFOs come with their own headaches. The "push the button and magic happens" is a lot trickier but maybe that was badly phrased?
I'm writing a linux application using C++ and wxWidgets.
From my application, I need to send keyboard events to the window that currently has the focus (not belonging to my application!).
My questions are:
How can I find out what window has the focus?
How can I send a keyboard event to a window not belonging to my application?
Thanks
Daniele
XGetInputFocus(3).
X11 does not care about "applications". There are only windows. It's enough to have a window ID (Window is the Xlib data type). Use whatever method of sending events works. There are two methods I know of: XSendEvent(3) and XTestFakeKeyEvent(3). The former method does not work with some programs that chose to ignore events coming from XSendEvent. The latter one requires the XTest extension, which is present in most, but not all, modern servers.
Note that InputFocus is a valid window designator for XSendEvent, and XTestFakeKeyEvent is delivered to the window that has the focus anyway, so you probably don't need to call XGetInputFocus at all.
If you use 2.9, you can use wxUIActionSimulator. It is intended to work with other windows of the same (wxWidgets) application but AFAICS it should actually work with the windows of other applications when using X11 too (however I didn't test it myself).
I am trying to write a program that monitors when the screen has been redrawn.
Meaning if any part of any window is redrawn, then the program is notified.
As far as I understand I should use a journal record hook like at
http://www.vbaccelerator.com/home/vb/code/libraries/Hooks/Journal_Record_Hooks/article.asp
However, I do not understand which MSG type would get me the WM_PAINT events (WH_CALLWNDPROC and WH_CALLWNDPROCRET do not seem to do the job). I'm not even sure that WM_PAINT is what I'm looking for...
Basically, if I knew when the DC associated with GetDesktopWindow() has changed then my problem would be solved.
Question is: How do you monitor screen updates?
I don't believe this is possible without hooking the display driver. I can imagine there would be some serious performance implications if it were possible in general...
You would be better taking a screenshot every second or whatever. Every version of Windows has the little network icon in the tray always changing when you transfer data over a network, meaning the screen will be changing pretty much constantly.