# Capture a window (by title substring) or the full virtual screen to a PNG.
# Usage: powershell -File shot.ps1 <out.png> [titleSubstring]
param([string]$Out = "shot.png", [string]$Title = "")
Add-Type -AssemblyName System.Windows.Forms, System.Drawing
Add-Type @"
using System;
using System.Runtime.InteropServices;
public class W {
  [DllImport("user32.dll")] public static extern bool GetWindowRect(IntPtr h, out R r);
  [DllImport("user32.dll")] public static extern IntPtr GetForegroundWindow();
  [DllImport("user32.dll")] public static extern bool SetForegroundWindow(IntPtr h);
  [DllImport("user32.dll")] public static extern bool IsWindowVisible(IntPtr h);
  [DllImport("user32.dll")] public static extern int GetWindowText(IntPtr h, System.Text.StringBuilder s, int n);
  [DllImport("user32.dll")] public static extern bool EnumWindows(EnumProc cb, IntPtr p);
  public delegate bool EnumProc(IntPtr h, IntPtr p);
  public struct R { public int L, T, Rr, B; }
}
"@
function Cap($rect, $path) {
  $w = $rect.Rr - $rect.L; $h = $rect.B - $rect.T
  if ($w -le 0 -or $h -le 0) { return $false }
  $bmp = New-Object System.Drawing.Bitmap $w, $h
  $g = [System.Drawing.Graphics]::FromImage($bmp)
  $g.CopyFromScreen($rect.L, $rect.T, 0, 0, (New-Object System.Drawing.Size($w, $h)))
  $bmp.Save($path, [System.Drawing.Imaging.ImageFormat]::Png)
  $g.Dispose(); $bmp.Dispose(); return $true
}
if ($Title -ne "") {
  $found = @()
  $cb = [W+EnumProc]{ param($h,$p)
    if ([W]::IsWindowVisible($h)) {
      $sb = New-Object System.Text.StringBuilder 256
      [void][W]::GetWindowText($h, $sb, 256)
      $t = $sb.ToString()
      if ($t -like "*$Title*") { $script:found += @{H=$h; T=$t} }
    }
    return $true
  }
  [void][W]::EnumWindows($cb, [IntPtr]::Zero)
  Write-Host "Matched windows:"; $found | ForEach-Object { Write-Host "  '$($_.T)'" }
  $i = 0
  foreach ($f in $found) {
    $r = New-Object W+R; [void][W]::GetWindowRect($f.H, [ref]$r)
    [void][W]::SetForegroundWindow($f.H); Start-Sleep -Milliseconds 250
    $p = $Out -replace '\.png$', "_$i.png"
    if (Cap $r $p) { Write-Host "saved $p ($($r.Rr-$r.L)x$($r.B-$r.T)) '$($f.T)'" }
    $i++
  }
} else {
  $vs = [System.Windows.Forms.SystemInformation]::VirtualScreen
  $r = New-Object W+R; $r.L=$vs.Left; $r.T=$vs.Top; $r.Rr=$vs.Right; $r.B=$vs.Bottom
  [void](Cap $r $Out); Write-Host "saved $Out (full screen $($vs.Width)x$($vs.Height))"
}