Is there some event or notification I can receive or hook each time an external LCD monitor is plugged in or unplugged from a laptop running Windows 7?
The laptop detects this and switches my display to the external screen and back with certain kinds of resizing or repositioning but is this exposed by the operating system so that applications can provide a handler, attach a script, etc?
If not, is there a registry setting or API I could poll from time to time?
(I prefer programming C + Win32 API)
UPDATE
Mike's answer below, WM_DEVICECHANGE led me to RegisterDeviceNotification(), but I'm struggling to implement it so far...
UPDATE 2
This question has been asked with different wording a couple of times, but not fully answered yet in my opinion:
How to detect hot plugging of monitor in a win32 application?
Getting an event on monitor hotplug for windows
According to this article Windows sends the WM_DISPLAYCHANGE message when display resolution changes and also when a display is added or removed.
If you need to react to desktop size changes due to monitor addition or removal, you can do so in the handler of this message. The LPARAM gives you the new resolution of the display on which the window is located. Notice that this resolution will be scaled if you use anything else than 100% for system DPI scaling and your program is not DPI-aware.
Alternatively use the EnumDisplayMonitors function to get the display resolution for each connected monitor and the relative positions of the monitors in the virtual desktop. This functions uses the real device pixel values regardless of DPI scaling.
You can try WM_DEVICECHANGE. If that doesn't do the trick, run your window and attach Spy++ to it which will log all the window messages it receives. Then plug your monitor in and check if you received any messages.
Alternatively you can poll GetSystemMetrics() with SM_CMONITORS.
As said here:
You will see registered messages "UxdDisplayChangeMessage" and "HotplugDetected" (second one only when adding monitor). You can use RegisterWindowMessage to get the identifier for these messages.
There are also other messages you can check, just see the linked answer.
Related
When you press Identify button in Screen Resolution dialog then Windows shows you big white monitor numbers on each monitor. It was easy to find them programmatically together with monitor coordinates in Windows XP (with EnumDisplayDevices) but on Windows 7 it's broken. How can I do that?
EnumDisplayDevices and GetMonitorInfo are not reliable anymore for that purpose in Windows 7.
I tried GetMonitorInfo and then extracting monitor number from MONITORINFOEX.szDevice (I.E. \.\Display2) with no success. Another guy did that too two years ago and claimed that getMonitorInfo has a bug. This bug was marked as fixed by Microsoft without any comments but it still can be reproduced on a win7 machine having latest updates. (Btw, can anybody tell me - maybe this bug is absent on win8 ?)
I tried QueryDisplayConfig from new CCD API but didn't find needed info.
Does anybody know the way?
Windows does not provide a function that allows applications to obtain the numbers used by the display settings app. The numbers themselves are specific only to the display settings app and have no meaning in the system or in the CCD APIs used to query/set the display topology.
The best option is for applications to define their own criteria for assigning an index when prompting the user to select a display.
I have never wanted to know in my Windows applications the number of monitors, but you can call GetSystemMetrics function with parameter value SM_CMONITORS to get the number of display monitors on a desktop.
I call in my Windows applications function GetSystemMetrics mainly with the parameter values SM_CXVIRTUALSCREEN, SM_CYVIRTUALSCREEN, SM_XVIRTUALSCREEN and SM_YVIRTUALSCREEN to avoid opening application windows completely or partly outside the display area. An application window could be nevertheless not visible if the user has extended the display area over multiple monitors, but not all of them are turned on.
The SystemParametersInfo function function with value SPI_GETWORKAREA for uiAction parameter is also very useful to know where an application window can be positioned and how large it can be in width and height on primary screen without being partly hidden by other windows (bars) being always on top.
See also GetMonitorInfo function if more informations from the monitors are required in your Windows application.
For Windows versions supporting WDDM, which Windows 7 does, you can simply use DXGI which is part of DirectX. DXGI allows you to very easily enumerate the existing display adapters, the available display outputs per adapter and the supported display modes per display output. While enumerating there's a lot of additional data you can read out, like handles, identifiers and device names. All of this can easily be used to retrieve the working areas as well. The order in which adapters and outputs are enumerated is defined by the system and matches the order of your configuration screen.
See here for more information: MSDN DXGI Overview
When you press Identify button in Screen Resolution dialog then Windows shows you big white monitor numbers on each monitor. It was easy to find them programmatically together with monitor coordinates in Windows XP (with EnumDisplayDevices) but on Windows 7 it's broken. How can I do that?
EnumDisplayDevices and GetMonitorInfo are not reliable anymore for that purpose in Windows 7.
I tried GetMonitorInfo and then extracting monitor number from MONITORINFOEX.szDevice (I.E. \.\Display2) with no success. Another guy did that too two years ago and claimed that getMonitorInfo has a bug. This bug was marked as fixed by Microsoft without any comments but it still can be reproduced on a win7 machine having latest updates. (Btw, can anybody tell me - maybe this bug is absent on win8 ?)
I tried QueryDisplayConfig from new CCD API but didn't find needed info.
Does anybody know the way?
Windows does not provide a function that allows applications to obtain the numbers used by the display settings app. The numbers themselves are specific only to the display settings app and have no meaning in the system or in the CCD APIs used to query/set the display topology.
The best option is for applications to define their own criteria for assigning an index when prompting the user to select a display.
I have never wanted to know in my Windows applications the number of monitors, but you can call GetSystemMetrics function with parameter value SM_CMONITORS to get the number of display monitors on a desktop.
I call in my Windows applications function GetSystemMetrics mainly with the parameter values SM_CXVIRTUALSCREEN, SM_CYVIRTUALSCREEN, SM_XVIRTUALSCREEN and SM_YVIRTUALSCREEN to avoid opening application windows completely or partly outside the display area. An application window could be nevertheless not visible if the user has extended the display area over multiple monitors, but not all of them are turned on.
The SystemParametersInfo function function with value SPI_GETWORKAREA for uiAction parameter is also very useful to know where an application window can be positioned and how large it can be in width and height on primary screen without being partly hidden by other windows (bars) being always on top.
See also GetMonitorInfo function if more informations from the monitors are required in your Windows application.
For Windows versions supporting WDDM, which Windows 7 does, you can simply use DXGI which is part of DirectX. DXGI allows you to very easily enumerate the existing display adapters, the available display outputs per adapter and the supported display modes per display output. While enumerating there's a lot of additional data you can read out, like handles, identifiers and device names. All of this can easily be used to retrieve the working areas as well. The order in which adapters and outputs are enumerated is defined by the system and matches the order of your configuration screen.
See here for more information: MSDN DXGI Overview
When you press Identify button in Screen Resolution dialog then Windows shows you big white monitor numbers on each monitor. It was easy to find them programmatically together with monitor coordinates in Windows XP (with EnumDisplayDevices) but on Windows 7 it's broken. How can I do that?
EnumDisplayDevices and GetMonitorInfo are not reliable anymore for that purpose in Windows 7.
I tried GetMonitorInfo and then extracting monitor number from MONITORINFOEX.szDevice (I.E. \.\Display2) with no success. Another guy did that too two years ago and claimed that getMonitorInfo has a bug. This bug was marked as fixed by Microsoft without any comments but it still can be reproduced on a win7 machine having latest updates. (Btw, can anybody tell me - maybe this bug is absent on win8 ?)
I tried QueryDisplayConfig from new CCD API but didn't find needed info.
Does anybody know the way?
Windows does not provide a function that allows applications to obtain the numbers used by the display settings app. The numbers themselves are specific only to the display settings app and have no meaning in the system or in the CCD APIs used to query/set the display topology.
The best option is for applications to define their own criteria for assigning an index when prompting the user to select a display.
I have never wanted to know in my Windows applications the number of monitors, but you can call GetSystemMetrics function with parameter value SM_CMONITORS to get the number of display monitors on a desktop.
I call in my Windows applications function GetSystemMetrics mainly with the parameter values SM_CXVIRTUALSCREEN, SM_CYVIRTUALSCREEN, SM_XVIRTUALSCREEN and SM_YVIRTUALSCREEN to avoid opening application windows completely or partly outside the display area. An application window could be nevertheless not visible if the user has extended the display area over multiple monitors, but not all of them are turned on.
The SystemParametersInfo function function with value SPI_GETWORKAREA for uiAction parameter is also very useful to know where an application window can be positioned and how large it can be in width and height on primary screen without being partly hidden by other windows (bars) being always on top.
See also GetMonitorInfo function if more informations from the monitors are required in your Windows application.
For Windows versions supporting WDDM, which Windows 7 does, you can simply use DXGI which is part of DirectX. DXGI allows you to very easily enumerate the existing display adapters, the available display outputs per adapter and the supported display modes per display output. While enumerating there's a lot of additional data you can read out, like handles, identifiers and device names. All of this can easily be used to retrieve the working areas as well. The order in which adapters and outputs are enumerated is defined by the system and matches the order of your configuration screen.
See here for more information: MSDN DXGI Overview
When you press Identify button in Screen Resolution dialog then Windows shows you big white monitor numbers on each monitor. It was easy to find them programmatically together with monitor coordinates in Windows XP (with EnumDisplayDevices) but on Windows 7 it's broken. How can I do that?
EnumDisplayDevices and GetMonitorInfo are not reliable anymore for that purpose in Windows 7.
I tried GetMonitorInfo and then extracting monitor number from MONITORINFOEX.szDevice (I.E. \.\Display2) with no success. Another guy did that too two years ago and claimed that getMonitorInfo has a bug. This bug was marked as fixed by Microsoft without any comments but it still can be reproduced on a win7 machine having latest updates. (Btw, can anybody tell me - maybe this bug is absent on win8 ?)
I tried QueryDisplayConfig from new CCD API but didn't find needed info.
Does anybody know the way?
Windows does not provide a function that allows applications to obtain the numbers used by the display settings app. The numbers themselves are specific only to the display settings app and have no meaning in the system or in the CCD APIs used to query/set the display topology.
The best option is for applications to define their own criteria for assigning an index when prompting the user to select a display.
I have never wanted to know in my Windows applications the number of monitors, but you can call GetSystemMetrics function with parameter value SM_CMONITORS to get the number of display monitors on a desktop.
I call in my Windows applications function GetSystemMetrics mainly with the parameter values SM_CXVIRTUALSCREEN, SM_CYVIRTUALSCREEN, SM_XVIRTUALSCREEN and SM_YVIRTUALSCREEN to avoid opening application windows completely or partly outside the display area. An application window could be nevertheless not visible if the user has extended the display area over multiple monitors, but not all of them are turned on.
The SystemParametersInfo function function with value SPI_GETWORKAREA for uiAction parameter is also very useful to know where an application window can be positioned and how large it can be in width and height on primary screen without being partly hidden by other windows (bars) being always on top.
See also GetMonitorInfo function if more informations from the monitors are required in your Windows application.
For Windows versions supporting WDDM, which Windows 7 does, you can simply use DXGI which is part of DirectX. DXGI allows you to very easily enumerate the existing display adapters, the available display outputs per adapter and the supported display modes per display output. While enumerating there's a lot of additional data you can read out, like handles, identifiers and device names. All of this can easily be used to retrieve the working areas as well. The order in which adapters and outputs are enumerated is defined by the system and matches the order of your configuration screen.
See here for more information: MSDN DXGI Overview
I have been working on windows automation and monitoring.
What exactly happens when I lock the screen of a windows machine?
I am working with Windows 7 at the moment, are there big differences to the behavior if I switch to Vista or the server versions?
Is there still a desktop that can be accessed via api's?
I know that i can still send key strokes and mouse clicks to specific windows (via ControlSend and ControlClick), but there seems to be no "desktop" itself.
Could someone shed some light on this whole thing or point me at a readable source where I could get an overview over the topic?
Basically what happens is that Windows switches to the secure desktop, makes it the current one, so input is now associated with it.
The old desktop remains where it was: all the HWNDs on the desktop are still there, and any thread attached to that desktop can still access those HWNDs, get their location, and so on. You can still send messages to windows on this desktop, so long as the thread sending the message is also on that desktop.
However, since the desktop is now inactive, it cannot receive input. GetForegroundWindow will return NULL (IIRC), and you can't use SendInput any longer, since input now belongs to [a thread on] a different desktop; no controls on that inactive desktop can receive focus.
Note that sending keypress messages to a control that doesn't have focus can sometimes cause unexpected behavior, since the app or control generally never expects to receive keyboard input without getting the focus first. (This can be problematic for controls that set up some sort of input context in WM_SETFOCUS and clear it up in WM_KILLFOCUS, for example.)
In short, the UI is still there: you can do certain queries against it, but you can no longer automate it as you could on a regular desktop by sending input, and some other functions that relate to focus or input may fail.
I'm not super familiar with AutoHotKey, but the name and description of functionality suggests that it's heavily reliant on the underlying Win32 SendInput API. This won't work at all for keyboard input when a desktop is inactive.
For a reasonable overview of how desktops work and how they relate to winstations, the locked desktop, and so on, check out the Desktop article on MSDN.
One issue that I've run into in the past with desktops and automation is: how to I leave a long-running test that's using some form of user input automation (mouse, keyboard simulation), but still lock my PC so that someone can't just walk by and interfere with it. Once you lock the PC, the desktop is inactive, and so the automation stops working. A similar issue happens if the screensaver kicks in: the desktop switches, and the automation fails.
One solution is to use two PCs: let's call them Main and Test: from Main, open a remote terminal services client onto the Test machine, and then run the automated test on the test machine, but from a terminal services client window on the Main machine. Now the cool part: you can minimize that TSC window, or even lock the Main machine (or let the screensaver kick in), and that virtual session will continue working, thinking that it is still active - it's just that nobody is paying it any attention. This is one way to create a "connected" session with an active desktop, but one that no-one can interfere with, because it's protected behind the locked desktop of the Main machine.
I don't know the details, but I believe the lock screen constitutes a separate "desktop" and maybe also a separate "window station" (as I understand it a window station is merely a container for desktops). The MSDN section on window stations should hopefully be useful: http://msdn.microsoft.com/en-us/library/windows/desktop/ms687098%28v=vs.85%29.aspx
In order to access a desktop, you will need to use the regular windows api's from a thread that is on that desktop. SetThreadDesktop would probably be the easiest way to do that in C, as long as the desktop isn't on a different window station.
Unfortunately, this is already difficult for a regular privileged application, and using AutoHotkey complicates it even more. Since you don't have control over threads or over process initialization, you will probably have to create a new process in the other desktop (you can do this using the CreateProcess API, which appears to have a wrapper available for AHK to which you can supply a desktop name: http://www.autohotkey.com/forum/topic1952.html). Your process will need special privileges to do this; I'm not sure that even running as Administrator is enough.