How to detect the current screen resolution?

How do I from Winapi (in C or C++) detect the current screen resolution?

Some background:

I want to start a new OpenGL fullscreen window, but want it open with the same horizo开发者_开发百科ntal and vertical size which the desktop already is set to. (Now when everyone uses LCD screens, I figured this is the best way to get the native resolution of the screen.)

I don't desperately need to also know the desktop color depth, although that would be a nice bonus.

• Size of the primary monitor: GetSystemMetrics SM_CXSCREEN / SM_CYSCREEN (GetDeviceCaps can also be used)
• Size of all monitors (combined): GetSystemMetrics SM_CX/YVIRTUALSCREEN
• Size of work area (screen excluding taskbar and other docked bars) on primary monitor: SystemParametersInfo SPI_GETWORKAREA
• Size of a specific monitor (work area and "screen"): GetMonitorInfo

Edit: It is important to remember that a monitor does not always "begin" at 0x0 so just knowing the size is not enough to position your window. You can use MonitorFromWindow to find the monitor your window is on and then call GetMonitorInfo

If you want to go the low-level route or change the resolution you need to use EnumDisplayDevices, EnumDisplaySettings and ChangeDisplaySettings (This is the only way to get the refresh rate AFAIK, but GetDeviceCaps will tell you the color depth)

When system use DPI virtualization (Vista and above) using GetSystemMetrics or GetWindowRect will fail to get the real screen resolution (you will get the virtual resolution) unless you created DPI Aware Application.

So the best option here (simple and backward compatible) is to use EnumDisplaySettings with ENUM_CURRENT_SETTINGS.

It's GetSystemMetrics with these parameters:
SM_CXSCREEN < width
SM_CYSCREEN < height

As it says (SM_CXSCREEN):

The width of the screen of the primary display monitor, in pixels. This is the same value obtained by calling GetDeviceCaps as follows: GetDeviceCaps( hdcPrimaryMonitor, HORZRES).

I think SystemParametersInfo might be useful.

Edit: Look at GetMonitorInfo too.

MFC Example Multiple monitor support with GetSystemMetrics EnumDisplayMonitors and GetMonitorInfo

Follow this link: Monitor enumeration with source code

I use the GetSystemMetrics function

GetSystemMetrics(SM_CXSCREEN) returns screen width(in pixels)

GetSystemMetrics(SM_CYSCREEN) - height in pixels

https://msdn.microsoft.com/en-us/library/windows/desktop/ms724385%28v=vs.85%29.aspx

Deleted about a week ago, then edited 3-4-13.

Here's a good one for situations where the user has decided to run their desktop in a lower resolution (bad idea) or corner cases where a person decided to get a monitor that their graphics controller couldn't take full advantage of:

// get actual size of desktop
RECT actualDesktop;
GetWindowRect(GetDesktopWindow(), &actualDesktop);

To get real monitor resolution

void GetMonitorRealResolution(HMONITOR monitor, int* pixelsWidth, int* pixelsHeight)
{
    MONITORINFOEX info = { sizeof(MONITORINFOEX) };
    winrt::check_bool(GetMonitorInfo(monitor, &info));
    DEVMODE devmode = {};
    devmode.dmSize = sizeof(DEVMODE);
    winrt::check_bool(EnumDisplaySettings(info.szDevice, ENUM_CURRENT_SETTINGS, &devmode));
    *pixelsWidth = devmode.dmPelsWidth;
    *pixelsHeight = devmode.dmPelsHeight;
}

It will return that native resolution in any case, even if the OS tries to lie to you due to the DPI awareness of the process.

To get the scaling ratio between the virtual resolution and real resolution

float GetMonitorScalingRatio(HMONITOR monitor)
{
    MONITORINFOEX info = { sizeof(MONITORINFOEX) };
    winrt::check_bool(GetMonitorInfo(monitor, &info));
    DEVMODE devmode = {};
    devmode.dmSize = sizeof(DEVMODE);
    winrt::check_bool(EnumDisplaySettings(info.szDevice, ENUM_CURRENT_SETTINGS, &devmode));
    return (info.rcMonitor.right - info.rcMonitor.left) / static_cast<float>(devmode.dmPelsWidth);
}

This will give you a ratio of the real resolution relative to the virtual resolution of the given monitor.

If the main DPI of the main monitor is 225% and on the second monitor it is 100%, and you run this function for the second monitor, you will get 2.25. because 2.25 * real resolution = the virtual resolution of the monitor.

If the second monitor has 125% scaling (while the main monitor is still 225% scaling), then this function will return you 1.79999995 because 125% relative to 225% is this value (225/125 = 1.8), and again - 1.8 * real resolution=the virtual resolution of 125%`

To get the real DPI value (not relative to anything)

Given that monitor, A has 225% DPI, and monitor B has 125% DPI, as I said above, you will not get 1.25 for the second monitor (if you run the function on the second monitor. You will get 1.8 as I said).

To overcome this, use this function:

float GetRealDpiForMonitor(HMONITOR monitor)
{
    return GetDpiForSystem() / 96.0 / GetMonitorScalingRatio(monitor);
}

This function depends on the previous function that I wrote above (the function GetMonitorScalingRatio that you need to copy)

This will give you the correct value