Get Windows DPI scaling factor

GetDpiForMonitor.tcl

package require Ffidl

if {$::tcl_platform(osVersion) >= 6.3} {

namespace eval USER32 {
	set MONITOR_DEFAULTTONULL    0x00
	set MONITOR_DEFAULTTOPRIMARY 0x01
	set MONITOR_DEFAULTTONEAREST 0x02
	
	ffidl::callout MonitorFromWindow {int int} int [ffidl::symbol user32.dll MonitorFromWindow]
}

namespace eval SHCore {
	set MDT_EFFECTIVE_DPI 0
	set MDT_ANGULAR_DPI 1
	set MDT_RAW_DPI 2
	set MDT_DEFAULT $MDT_EFFECTIVE_DPI
	
	ffidl::callout GetDpiForMonitor {pointer int pointer-var pointer-var} int [ffidl::symbol SHCore.dll GetDpiForMonitor]
}

proc get_dpi {MONITOR_DPI_TYPE} {
	set hwnd [winfo id .]
	
	set hmon [USER32::MonitorFromWindow $hwnd $USER32::MONITOR_DEFAULTTONEAREST]
	
	set bxdpi [binary format i 0]
	set bydpi [binary format i 0]
	SHCore::GetDpiForMonitor $hmon $MONITOR_DPI_TYPE bxdpi bydpi
	binary scan $bxdpi iu xdpi
	binary scan $bydpi iu ydpi
	
	list $xdpi $ydpi
}

proc get_effective_dpi_factor {} {
	lassign [get_dpi $SHCore::MDT_EFFECTIVE_DPI] xdpi ydpi
	expr {$xdpi / 96.0}
}

}