Screen resolution in mm

Question

Is it possible to get screen pixel resolution in mm using the Win32 API? I have an application that shows 0.347222222222222222 as the value for this on my monitor at 1280x1024 with a resolution of 96 dpi. But I can’t find out how it happened. Any hints would be helpful. I can also use MFC if necessary.

EDIT Sorry for the confusion, the software I'm talking about doesn't use the current screen resolution. He read it from some configuration file.

Answer 1

Get device covers for the monitor gives you the size in pixels and mm, thus:

HDC screen = GetDC(NULL);
int hSize=GetDeviceCaps(screen,HORZSIZE);
int hRes=GetDeviceCaps(screen,HORZRES);
float PixelsPerMM=(float)hRes/hSize;   // pixels per millimeter
float PixelsPerInch=PixelsPerMM*25.4; //dpi

Answer 2

0,3472222222222222 73 dpi. Windows 72dpi 96dpi, . . , 96- 72dpi, , .

Windows 72dpi, , ( "" ) , . 0.34, , 72dpi . , , Word, , 100%, . , .

Answer 3

DPI MSDN , . API .

Answer 4

Windows 7 , , : http://ofekshilon.com/2011/11/13/reading-monitor-physical-dimensions-or-getting-the-edid-the-right-way/

!

#include <atlstr.h>
#include <SetupApi.h>
#pragma comment(lib, "setupapi.lib")

#define NAME_SIZE 128

const GUID GUID_CLASS_MONITOR = {0x4d36e96e, 0xe325, 0x11ce, 0xbf, 0xc1, 0x08, 0x00, 0x2b, 0xe1, 0x03, 0x18};

// Assumes hDevRegKey is valid
bool GetMonitorSizeFromEDID(const HKEY hDevRegKey, short& WidthMm, short& HeightMm)
{
    DWORD dwType, AcutalValueNameLength = NAME_SIZE;
    TCHAR valueName[NAME_SIZE];

    BYTE EDIDdata[1024];
    DWORD edidsize=sizeof(EDIDdata);

    for (LONG i = 0, retValue = ERROR_SUCCESS; retValue != ERROR_NO_MORE_ITEMS; ++i)
    {
        retValue = RegEnumValue ( hDevRegKey, i, &valueName[0],
            &AcutalValueNameLength, NULL, &dwType,
            EDIDdata, // buffer
            &edidsize); // buffer size

        if (retValue != ERROR_SUCCESS || 0 != _tcscmp(valueName,_T("EDID")))
            continue;

        WidthMm  = ((EDIDdata[68] & 0xF0) << 4) + EDIDdata[66];
        HeightMm = ((EDIDdata[68] & 0x0F) << 8) + EDIDdata[67];

        return true; // valid EDID found
    }

    return false; // EDID not found
}

bool GetSizeForDevID(const CString& TargetDevID, short& WidthMm, short& HeightMm)
{
    HDEVINFO devInfo = SetupDiGetClassDevsEx(
        &GUID_CLASS_MONITOR, //class GUID
        NULL, //enumerator
        NULL, //HWND
        DIGCF_PRESENT, // Flags //DIGCF_ALLCLASSES|
        NULL, // device info, create a new one.
        NULL, // machine name, local machine
        NULL);// reserved

    if (NULL == devInfo)
        return false;

    bool bRes = false;

    for (ULONG i=0; ERROR_NO_MORE_ITEMS != GetLastError(); ++i)
    {
        SP_DEVINFO_DATA devInfoData;
        memset(&devInfoData,0,sizeof(devInfoData));
        devInfoData.cbSize = sizeof(devInfoData);

        if (SetupDiEnumDeviceInfo(devInfo,i,&devInfoData))
        {
            HKEY hDevRegKey = SetupDiOpenDevRegKey(devInfo,&devInfoData,
                DICS_FLAG_GLOBAL, 0, DIREG_DEV, KEY_READ);

            if(!hDevRegKey || (hDevRegKey == INVALID_HANDLE_VALUE))
                continue;

            bRes = GetMonitorSizeFromEDID(hDevRegKey, WidthMm, HeightMm);

            RegCloseKey(hDevRegKey);
        }
    }
    SetupDiDestroyDeviceInfoList(devInfo);
    return bRes;
}

int _tmain(int argc, _TCHAR* argv[])
{
    short WidthMm, HeightMm;

    DISPLAY_DEVICE dd;
    dd.cb = sizeof(dd);
    DWORD dev = 0; // device index
    int id = 1; // monitor number, as used by Display Properties > Settings

    CString DeviceID;
    bool bFoundDevice = false;
    while (EnumDisplayDevices(0, dev, &dd, 0) && !bFoundDevice)
    {
        DISPLAY_DEVICE ddMon;
        ZeroMemory(&ddMon, sizeof(ddMon));
        ddMon.cb = sizeof(ddMon);
        DWORD devMon = 0;

        while (EnumDisplayDevices(dd.DeviceName, devMon, &ddMon, 0) && !bFoundDevice)
        {
            if (ddMon.StateFlags & DISPLAY_DEVICE_ACTIVE &&
                !(ddMon.StateFlags & DISPLAY_DEVICE_MIRRORING_DRIVER))
            {
                DeviceID.Format (L"%s", ddMon.DeviceID);
                DeviceID = DeviceID.Mid (8, DeviceID.Find (L"\\", 9) - 8);

                bFoundDevice = GetSizeForDevID(DeviceID, WidthMm, HeightMm);
            }
            devMon++;

            ZeroMemory(&ddMon, sizeof(ddMon));
            ddMon.cb = sizeof(ddMon);
        }

        ZeroMemory(&dd, sizeof(dd));
        dd.cb = sizeof(dd);
        dev++;
    }

    return 0;
}

Answer 5

Use the GetDC function to get the handle on the monitor, then call GetDeviceCaps to get the size of the monitor in millimeters. For example:

HDC monitor = GetDC( NULL );
int horizSize = GetDeviceCaps( monitor, HORZSIZE );
int vertSize = GetDeviceCaps( monitor, VERTSIZE );

Answer 6

The code snippet below showed the best result.

ID2D1Factory* m_pDirect2dFactory;
D2D1CreateFactory(D2D1_FACTORY_TYPE_SINGLE_THREADED, &m_pDirect2dFactory);
FLOAT dpiX, dpiY;
m_pDirect2dFactory->GetDesktopDpi( &dpiX, &dpiY );