Test: Count a parked window at its nearest monitor's scale

scripts/tests/windows-features-lib.ps1

@@ -497,3 +497,15 @@ function Test-FirstFrames($Frames, $Steady, [int]$X0, [int]$X1, [int]$Y1) {
 function Test-VisibleBreach([bool]$OnMonitor, [string]$TestDesktop) {
   $OnMonitor -and -not $TestDesktop
 }
+
+# Why a parked window's scale does not count, or $null when it does. `Scales` are the layout DPIs
+# the runtime traced for the window, first to last, and `MonitorDpi` is the DPI of the monitor the
+# park is nearest. A window opened on one monitor and parked nearest another of another scale
+# rightly takes that monitor's scale. Any other scale, such as the system scale a window level with
+# a monitor's band can drop to, would run every row at a scale no person's window has there.
+function Get-ParkScaleError([int[]]$Scales, [int]$MonitorDpi) {
+  if (-not $Scales -or $Scales.Count -eq 0 -or $MonitorDpi -le 0) { return $null }
+  $settled = $Scales[-1]
+  if ($settled -eq $MonitorDpi) { return $null }
+  "the parked window settled at scale $settled (first $($Scales[0])), not at its nearest monitor's $MonitorDpi"
+}

scripts/tests/windows-features.ps1

@@ -76,6 +76,10 @@ public static class FeatureWin{
  [DllImport("user32.dll")] public static extern uint GetWindowThreadProcessId(IntPtr h,out uint p);
  [DllImport("user32.dll")] public static extern bool IsWindowVisible(IntPtr h);
  [DllImport("user32.dll")] public static extern bool IsWindow(IntPtr h);
+ [DllImport("user32.dll")] static extern IntPtr MonitorFromWindow(IntPtr h,uint f);
+ [DllImport("shcore.dll")] static extern int GetDpiForMonitor(IntPtr m,int type,out uint x,out uint y);
+ // The effective DPI of the monitor nearest the window, or 0 when it cannot be read.
+ public static int NearestMonitorDpi(IntPtr h){uint x,y;return GetDpiForMonitor(MonitorFromWindow(h,2),0,out x,out y)==0?(int)x:0;}
  [DllImport("user32.dll")] public static extern IntPtr GetWindow(IntPtr h,uint c);
  [DllImport("user32.dll",CharSet=CharSet.Unicode)] public static extern int GetClassName(IntPtr h,StringBuilder s,int n);
  [DllImport("user32.dll",CharSet=CharSet.Unicode)] public static extern IntPtr GetProp(IntPtr h,string n);
@@ -300,13 +304,12 @@ function Open-Scene($ctx, $state, $Url, $Seed, [string[]]$Extra = @()) {
   [FeatureWin]::PostMessage($ctx.Hwnd, 0x86, [IntPtr]1, [IntPtr]0) | Out-Null
   Start-Sleep 8
   $dpi = Get-LayoutDpi $ctx
-  # The window must keep the scale it was first laid out at: a park that moves it to another scale
-  # would run every row at a scale no person's window has there.
+  # The parked window must settle at the scale of the monitor it is nearest, as a person's window
+  # there has; Get-ParkScaleError says why another scale does not count.
   $hex = '{0:x}' -f $ctx.Hwnd.ToInt64()
   $scales = @(Read-Log | Where-Object { $_ -match "^layout dpi: window 0x$hex at (\d+)$" } | ForEach-Object { [int]($_ -replace '.* at ', '') })
-  if ($scales.Count -ge 2 -and $scales[0] -ne $scales[-1] -and -not $ctx.Error) {
-    $ctx.Error = "the window's scale changed after it was parked: $($scales[0]) then $($scales[-1])"
-  }
+  $parkScale = Get-ParkScaleError $scales ([FeatureWin]::NearestMonitorDpi($ctx.Hwnd))
+  if ($parkScale -and -not $ctx.Error) { $ctx.Error = $parkScale }
   if ($dpi) { $ctx.Dpi = $dpi } elseif (-not $ctx.Error) { $ctx.Error = 'the runtime traced no scale for the window' }
   # Every scene checks that the attach finished: the browser laid the window out for Rivet's frame.
   if (-not $ctx.Error) {

scripts/tests/windows-features.selftest.ps1

@@ -377,5 +377,23 @@ foreach ($case in @(@($true, '', $true), @($true, 'WinSta0\rivet-test-1', $false
 if ($breach) { Write-Host "FAIL nfr5_only_the_persons_desktop_has_visible_monitors : $breach cases"; $failures++ }
 else { Write-Host 'ok   nfr5_only_the_persons_desktop_has_visible_monitors' }
 
+# A parked window counts at its nearest monitor's scale only.
+$park = 0
+foreach ($case in @(
+    # Opened on a 200 percent primary, parked nearest a 125 percent monitor.
+    @(@(192, 120), 120, $true),
+    # One monitor at 200 percent: the window dropped to the system scale.
+    @(@(192, 96), 192, $false),
+    # Parked nearest a 125 percent monitor but left at the scale it opened at.
+    @(@(192), 120, $false),
+    @(@(120), 120, $true),
+    # No scale traced, or no monitor read: the scene's own checks say so.
+    @(@(), 120, $true),
+    @(@(192, 96), 0, $true))) {
+  if ([bool](-not (Get-ParkScaleError $case[0] $case[1])) -ne $case[2]) { $park++ }
+}
+if ($park) { Write-Host "FAIL nfr5_a_parked_window_counts_at_its_nearest_monitors_scale_only : $park cases"; $failures++ }
+else { Write-Host 'ok   nfr5_a_parked_window_counts_at_its_nearest_monitors_scale_only' }
+
 if ($failures) { Write-Host "$failures failed"; exit 1 }
 Write-Host 'windows-features selftest: all passed'