Add helper for centering dialog relative to a Control

src/BizHawk.Client.EmuHawk/Extensions/ControlExtensions.cs

@@ -74,6 +74,18 @@ public static ToolStripMenuItem ToColumnsMenu(this InputRoll inputRoll, Action c
 			return menu;
 		}
 
+		public static void CenterOn(this Form form, Control logicalParent)
+			=> form.CenterOn((logicalParent is Form ? logicalParent : logicalParent.Parent)
+				.ChildPointToScreen(logicalParent) + logicalParent.HalfSize());
+
+		public static void CenterOn(this Form form, Point point)
+		{
+			// not asserting `form` is closed at this point, but we could
+			point -= form.HalfSize();
+			form.StartPosition = FormStartPosition.Manual;
+			form.Location = point;
+		}
+
 		public static Point ChildPointToScreen(this Control control, Control child)
 		{
 			return control.PointToScreen(new Point(child.Location.X, child.Location.Y));
@@ -131,6 +143,9 @@ public static T Clone<T>(this T controlToClone)
 		public static IEnumerable<Control> Controls(this Control control)
 			=> control.Controls.Cast<Control>();
 
+		public static Size HalfSize(this Control c)
+			=> new(c.Width / 2, c.Height / 2);
+
 		public static IEnumerable<TabPage> TabPages(this TabControl tabControl)
 		{
 			return tabControl.TabPages.Cast<TabPage>();

src/BizHawk.Client.EmuHawk/tools/TAStudio/TAStudio.MenuItems.cs

@@ -953,24 +953,23 @@ private void LoadBranchOnDoubleClickMenuItem_Click(object sender, EventArgs e)
 
 		private void HeaderMenuItem_Click(object sender, EventArgs e)
 		{
-			new MovieHeaderEditor(CurrentTasMovie, Config)
-			{
-				Owner = Owner,
-				Location = this.ChildPointToScreen(TasView)
-			}.Show();
+			MovieHeaderEditor form = new(CurrentTasMovie, Config) { Owner = this.Owner/*uhh*/ };
+			form.CenterOn(TasView);
+			form.Show();
 		}
 
 		private void StateHistorySettingsMenuItem_Click(object sender, EventArgs e)
 		{
-			new GreenzoneSettings(
+			GreenzoneSettings form = new(
 				DialogController,
 				new ZwinderStateManagerSettings(CurrentTasMovie.TasStateManager.Settings),
 				(s, k) => { CurrentTasMovie.TasStateManager.UpdateSettings(s, k); },
 				false)
 			{
-				Location = this.ChildPointToScreen(TasView),
-				Owner = Owner
-			}.ShowDialog();
+				Owner = this.Owner, // uhh
+			};
+			form.CenterOn(TasView);
+			form.ShowDialog();
 		}
 
 		private void CommentsMenuItem_Click(object sender, EventArgs e)
@@ -987,15 +986,16 @@ private void SubtitlesMenuItem_Click(object sender, EventArgs e)
 
 		private void DefaultStateSettingsMenuItem_Click(object sender, EventArgs e)
 		{
-			new GreenzoneSettings(
+			GreenzoneSettings form = new(
 				DialogController,
 				new ZwinderStateManagerSettings(Config.Movies.DefaultTasStateManagerSettings),
 				(s, k) => { Config.Movies.DefaultTasStateManagerSettings = s; },
 				true)
 			{
-				Location = this.ChildPointToScreen(TasView),
-				Owner = Owner
-			}.ShowDialog();
+				Owner = this.Owner, // uhh
+			};
+			form.CenterOn(TasView);
+			form.ShowDialog();
 		}
 
 		private void SettingsSubMenu_DropDownOpened(object sender, EventArgs e)