It seems to be an overkill to depend on GDI+ for just GetDeviceCaps

[andrey-martynyuk]

Version/Branch of Dear ImGui:

Dear ImGui 1.76 (17600)
--------------------------------
define: __cplusplus=199711
define: _WIN32
define: _WIN64
define: _MSC_VER=1925
--------------------------------
io.BackendPlatformName: imgui_impl_win32
io.BackendRendererName: imgui_impl_dx11

Back-end/Renderer/Compiler/OS

Back-ends: imgui_impl_win32 + imgui_impl_dx11
Compiler: Microsoft Visual Studio 16.5.4
Operating System: Windows 10

My Issue/Question:

In version 1.75 ImGui didn't have a dependency on GDI+. So I happily used it with #define NOGDI defined in pch.h.

In version 1.76 ImGui_ImplWin32_GetDpiScaleForMonitor function was added. That brought dependency on GDI+ function GetDeviceCaps. Here is guilty code:

#ifdef _MSC_VER
#pragma comment(lib, "gdi32")   // Link with gdi32.lib for GetDeviceCaps()
#endif

float ImGui_ImplWin32_GetDpiScaleForMonitor(void* monitor)
{
    UINT xdpi = 96, ydpi = 96;
    if (IsWindows8Point1OrGreater())
    {
        static HINSTANCE shcore_dll = ::LoadLibraryA("shcore.dll"); // Reference counted per-process
        if (PFN_GetDpiForMonitor GetDpiForMonitorFn = (PFN_GetDpiForMonitor)::GetProcAddress(shcore_dll, "GetDpiForMonitor"))
            GetDpiForMonitorFn((HMONITOR)monitor, MDT_EFFECTIVE_DPI, &xdpi, &ydpi);
    }
    else
    {
        const HDC dc = ::GetDC(NULL);
        xdpi = ::GetDeviceCaps(dc, LOGPIXELSX);
        ydpi = ::GetDeviceCaps(dc, LOGPIXELSY);
        ::ReleaseDC(NULL, dc);
    }
    IM_ASSERT(xdpi == ydpi); // Please contact me if you hit this assert!
    return xdpi / 96.0f;
}

float ImGui_ImplWin32_GetDpiScaleForHwnd(void* hwnd)
{
    HMONITOR monitor = ::MonitorFromWindow((HWND)hwnd, MONITOR_DEFAULTTONEAREST);
    return ImGui_ImplWin32_GetDpiScaleForMonitor(monitor);
}

It seems to be an overkill to depend on GDI+ for just one function, which is used only on systems older than Windows 8!

Possible solution is to have this dependency under #ifndef NOGDI:

#ifndef NOGDI
    else
    {
        const HDC dc = ::GetDC(NULL);
        xdpi = ::GetDeviceCaps(dc, LOGPIXELSX);
        ydpi = ::GetDeviceCaps(dc, LOGPIXELSY);
        ::ReleaseDC(NULL, dc);
    }
#endif

If the client is opted out GDI+ and has its application running on Windows 7 or older, it's safe to assume GetDeviceCaps returned 96, I guess.

Standalone, minimal, complete and verifiable example:

#define NOGDI

[ocornut]

Hello,
I have merged the suggested changed along with the pragma line.
Thank you!
Ref #2327