vendor: import KillerPDF 1.7.5 source (GPL-3.0) as the base for MMD PDF

Controls/WindowFx.cs

@@ -0,0 +1,33 @@
+using System;
+using System.Windows;
+using System.Windows.Media.Animation;
+
+namespace KillerPDF
+{
+
+    // Fade a window out on close: cancel the first close, animate opacity to 0, then close for real.
+    // DialogResult is set before Closing fires, so it survives the deferral.
+    internal static class WindowFx
+    {
+        public const int FadeMs = 150;
+
+        public static void EnableFadeClose(Window w, int ms = FadeMs)
+        {
+            bool fading = false;
+            bool readyToClose = false;
+            w.Closing += (s, e) =>
+            {
+                if (readyToClose) return;  // our own post-fade Close - let it through
+                e.Cancel = true;           // hold off the real close until the fade finishes
+                if (fading) return;        // already fading - ignore repeat triggers
+                fading = true;
+                var anim = new DoubleAnimation(w.Opacity, 0, new Duration(TimeSpan.FromMilliseconds(ms)))
+                {
+                    EasingFunction = new QuadraticEase { EasingMode = EasingMode.EaseOut }
+                };
+                anim.Completed += (_, _) => { readyToClose = true; w.Close(); };
+                w.BeginAnimation(UIElement.OpacityProperty, anim);
+            };
+        }
+    }
+}