# Switches the display scale between 100% and 200% for the current user.
# With no argument it toggles; -Scale 100 or -Scale 200 forces a value.
# The scale is stored in the registry (LogPixels), so the change takes effect only after
# a restart. Use -Restart to reboot right away.
param(
    [ValidateSet(0, 100, 200)]
    [int]$Scale = 0,
    [switch]$Restart
)

$ErrorActionPreference = 'Stop'

$desktopKey = 'HKCU:\Control Panel\Desktop'
$metricsKey = 'HKCU:\Control Panel\Desktop\WindowMetrics'

$logPixels = (Get-ItemProperty -Path $desktopKey -Name LogPixels -ErrorAction SilentlyContinue).LogPixels
if (-not $logPixels) { $logPixels = 96 }
$current = [int][math]::Round($logPixels * 100 / 96)

$target = if ($Scale -ne 0) { $Scale } elseif ($current -eq 100) { 200 } else { 100 }
$dpi = [int]($target * 96 / 100)

Write-Host "Scale: $current% -> $target%"

# Win8DpiScaling=1 makes Windows use LogPixels instead of the per-monitor recommendation.
Set-ItemProperty -Path $desktopKey -Name LogPixels -Type DWord -Value $dpi
Set-ItemProperty -Path $desktopKey -Name Win8DpiScaling -Type DWord -Value 1
Set-ItemProperty -Path $metricsKey -Name AppliedDPI -Type DWord -Value $dpi

Write-Host 'Restart Windows for the new scale to take effect.'
if ($Restart) {
    Write-Host 'Restarting in 5 seconds...'
    shutdown.exe /r /t 5
}