GetDpiForMonitor

// api-ms-win-shcore-scaling-l1-1-1.dll
#include <windows.h>

HRESULT GetDpiForMonitor(
    HMONITOR hmonitor,
    MONITOR_DPI_TYPE dpiType,
    DWORD* dpiX,
    DWORD* dpiY
);

<DllImport("api-ms-win-shcore-scaling-l1-1-1.dll", ExactSpelling:=True)>
Public Shared Function GetDpiForMonitor(
    hmonitor As IntPtr,   ' HMONITOR
    dpiType As Integer,   ' MONITOR_DPI_TYPE
    <Out> ByRef dpiX As UInteger,   ' DWORD* out
    <Out> ByRef dpiY As UInteger   ' DWORD* out
) As Integer
End Function

' hmonitor : HMONITOR
' dpiType : MONITOR_DPI_TYPE
' dpiX : DWORD* out
' dpiY : DWORD* out
Declare PtrSafe Function GetDpiForMonitor Lib "api-ms-win-shcore-scaling-l1-1-1" ( _
    ByVal hmonitor As LongPtr, _
    ByVal dpiType As Long, _
    ByRef dpiX As Long, _
    ByRef dpiY As Long) As Long
' VBA7前提(PtrSafe)。32bit Office では LongPtr→Long。Integer=16bit / Long=32bit / LongLong=64bit。

import ctypes
from ctypes import wintypes

GetDpiForMonitor = ctypes.windll.LoadLibrary("api-ms-win-shcore-scaling-l1-1-1.dll").GetDpiForMonitor
GetDpiForMonitor.restype = ctypes.c_int
GetDpiForMonitor.argtypes = [
    wintypes.HANDLE,  # hmonitor : HMONITOR
    ctypes.c_int,  # dpiType : MONITOR_DPI_TYPE
    ctypes.POINTER(wintypes.DWORD),  # dpiX : DWORD* out
    ctypes.POINTER(wintypes.DWORD),  # dpiY : DWORD* out
]

require 'fiddle'
require 'fiddle/import'

lib = Fiddle.dlopen('api-ms-win-shcore-scaling-l1-1-1.dll')
GetDpiForMonitor = Fiddle::Function.new(
  lib['GetDpiForMonitor'],
  [
    Fiddle::TYPE_VOIDP,  # hmonitor : HMONITOR
    Fiddle::TYPE_INT,  # dpiType : MONITOR_DPI_TYPE
    Fiddle::TYPE_VOIDP,  # dpiX : DWORD* out
    Fiddle::TYPE_VOIDP,  # dpiY : DWORD* out
  ],
  Fiddle::TYPE_INT)

#[link(name = "api-ms-win-shcore-scaling-l1-1-1")]
extern "system" {
    fn GetDpiForMonitor(
        hmonitor: *mut core::ffi::c_void,  // HMONITOR
        dpiType: i32,  // MONITOR_DPI_TYPE
        dpiX: *mut u32,  // DWORD* out
        dpiY: *mut u32  // DWORD* out
    ) -> i32;
}
// crates: windows-sys provides ready-made bindings for this API.

$sig = @"
[DllImport("api-ms-win-shcore-scaling-l1-1-1.dll")]
public static extern int GetDpiForMonitor(IntPtr hmonitor, int dpiType, out uint dpiX, out uint dpiY);
"@
$api = Add-Type -MemberDefinition $sig -Name 'api-ms-win-shcore-scaling-l1-1-1_GetDpiForMonitor' -Namespace Win32 -PassThru
# $api::GetDpiForMonitor(hmonitor, dpiType, dpiX, dpiY)

#uselib "api-ms-win-shcore-scaling-l1-1-1.dll"
#func global GetDpiForMonitor "GetDpiForMonitor" sptr, sptr, sptr, sptr
; GetDpiForMonitor hmonitor, dpiType, varptr(dpiX), varptr(dpiY)   ; 戻り値は stat
; hmonitor : HMONITOR -> "sptr"
; dpiType : MONITOR_DPI_TYPE -> "sptr"
; dpiX : DWORD* out -> "sptr"
; dpiY : DWORD* out -> "sptr"
; ※HSP3.7は #func のため戻り値はシステム変数 stat に格納されます。

#uselib "api-ms-win-shcore-scaling-l1-1-1.dll"
#cfunc global GetDpiForMonitor "GetDpiForMonitor" sptr, int, var, var
; res = GetDpiForMonitor(hmonitor, dpiType, dpiX, dpiY)
; hmonitor : HMONITOR -> "sptr"
; dpiType : MONITOR_DPI_TYPE -> "int"
; dpiX : DWORD* out -> "var"
; dpiY : DWORD* out -> "var"
; ※出力/バッファ引数は var 方式(変数を直接渡す)。varptr 方式にも切替可。

; HRESULT GetDpiForMonitor(HMONITOR hmonitor, MONITOR_DPI_TYPE dpiType, DWORD* dpiX, DWORD* dpiY)
#uselib "api-ms-win-shcore-scaling-l1-1-1.dll"
#cfunc global GetDpiForMonitor "GetDpiForMonitor" intptr, int, var, var
; res = GetDpiForMonitor(hmonitor, dpiType, dpiX, dpiY)
; hmonitor : HMONITOR -> "intptr"
; dpiType : MONITOR_DPI_TYPE -> "int"
; dpiX : DWORD* out -> "var"
; dpiY : DWORD* out -> "var"
; ※出力/バッファ引数は var 方式(変数を直接渡す)。varptr 方式にも切替可。

import (
	"golang.org/x/sys/windows"
	"unsafe"
)

var (
	api_ms_win_shcore_scaling_l1_1_1 = windows.NewLazySystemDLL("api-ms-win-shcore-scaling-l1-1-1.dll")
	procGetDpiForMonitor = api_ms_win_shcore_scaling_l1_1_1.NewProc("GetDpiForMonitor")
)

// hmonitor (HMONITOR), dpiType (MONITOR_DPI_TYPE), dpiX (DWORD* out), dpiY (DWORD* out)
r1, _, err := procGetDpiForMonitor.Call(
	uintptr(hmonitor),
	uintptr(dpiType),
	uintptr(dpiX),
	uintptr(dpiY),
)
_ = err  // syscall.Errno (valid when the call sets last-error)
_ = r1   // HRESULT

function GetDpiForMonitor(
  hmonitor: THandle;   // HMONITOR
  dpiType: Integer;   // MONITOR_DPI_TYPE
  dpiX: Pointer;   // DWORD* out
  dpiY: Pointer   // DWORD* out
): Integer; stdcall;
  external 'api-ms-win-shcore-scaling-l1-1-1.dll' name 'GetDpiForMonitor';

result := DllCall("api-ms-win-shcore-scaling-l1-1-1\GetDpiForMonitor"
    , "Ptr", hmonitor   ; HMONITOR
    , "Int", dpiType   ; MONITOR_DPI_TYPE
    , "Ptr", dpiX   ; DWORD* out
    , "Ptr", dpiY   ; DWORD* out
    , "Int")   ; return: HRESULT

●GetDpiForMonitor(hmonitor, dpiType, dpiX, dpiY) = DLL("api-ms-win-shcore-scaling-l1-1-1.dll", "int GetDpiForMonitor(void*, int, void*, void*)")
# 呼び出し: GetDpiForMonitor(hmonitor, dpiType, dpiX, dpiY)
# hmonitor : HMONITOR -> "void*"
# dpiType : MONITOR_DPI_TYPE -> "int"
# dpiX : DWORD* out -> "void*"
# dpiY : DWORD* out -> "void*"
# なでしこ1は32bit・ANSI(Shift_JIS)。文字列=char*(ANSI)、ポインタ/ハンドル=void*(4byte)。