Merge commit '0ec7e486b6e2315b12df663759660828d63728ae'

Author: larsbrubaker

Gui/Menu/PopupWidget.cs

@@ -380,29 +380,35 @@ private void RecalculatePosition(object sender, EventArgs e)
 				// we only check for the scroll bar one time (the first time we open)
 				if (checkIfNeedScrollBar)
 				{
-					var minimumOpenHeight = 50 * GuiWidget.DeviceScale;
-
-					// If the bottom of the popup is below the bottom of the screen
-					if (direction == Direction.Down)
+					// Opening Down puts the popup between the bottom of the anchor and the bottom of the window,
+					// opening Up puts it between the top of the anchor and the top of the window. Measure both,
+					// then prefer the requested direction, fall back to the other one, and only squeeze in a
+					// scroll bar when the popup fits in neither. windowToAddTo is the window the popup was
+					// actually added to (the outermost SystemWindow), which is the space these screen space
+					// coordinates are expressed in - a nearer SystemWindow ancestor would give the wrong height.
+					var spaceBelow = bottomLeftScreenSpace.Y;
+					var spaceAbove = windowToAddTo.Height - (bottomLeftScreenSpace.Y + widgetRelativeTo.Height);
+					var neededHeight = popupWidget.LocalBounds.Height;
+
+					var preferredSpace = direction == Direction.Down ? spaceBelow : spaceAbove;
+					var oppositeSpace = direction == Direction.Down ? spaceAbove : spaceBelow;
+
+					if (neededHeight > preferredSpace)
 					{
-						if (bottomLeftScreenSpace.Y - popupWidget.LocalBounds.Height < 0)
+						if (neededHeight <= oppositeSpace)
 						{
-							if (bottomLeftScreenSpace.Y <= minimumOpenHeight)
-							{
-								direction = Direction.Up;
-							}
-							else
-							{
-								popupWidget.MakeMenuHaveScroll(bottomLeftScreenSpace.Y - 5);
-							}
+							direction = direction == Direction.Down ? Direction.Up : Direction.Down;
 						}
-					}
-					else
-					{
-						SystemWindow windowToAddTo = widgetRelativeTo.Parents<SystemWindow>().FirstOrDefault();
-						if (bottomLeftScreenSpace.Y + popupWidget.LocalBounds.Height > windowToAddTo.Height)
+						else
 						{
-							popupWidget.MakeMenuHaveScroll(bottomLeftScreenSpace.Y - 5);
+							// It fits nowhere, so open toward whichever side has more room (keeping the
+							// preferred direction on a tie) and scroll within that space
+							if (oppositeSpace > preferredSpace)
+							{
+								direction = direction == Direction.Down ? Direction.Up : Direction.Down;
+							}
+
+							popupWidget.MakeMenuHaveScroll(Math.Max(preferredSpace, oppositeSpace) - 5);
 						}
 					}
 

Tests/Agg.Tests/Agg.UI/PopupDirectionFlipTests.cs

@@ -0,0 +1,116 @@
+/*
+Copyright (c) 2026, Lars Brubaker
+All rights reserved.
+*/
+
+using System.Linq;
+using System.Threading.Tasks;
+using MatterHackers.GuiAutomation;
+using MatterHackers.VectorMath;
+using TUnit.Assertions;
+using TUnit.Core;
+
+namespace MatterHackers.Agg.UI.Tests
+{
+	/// <summary>
+	/// A drop down opened near the bottom of the window used to stay open downward and grow a scroll
+	/// bar as long as there were more than 50 pixels below it, even when the whole list would have fit
+	/// above the anchor. These tests pin the symmetric rule: use the preferred direction if it fits,
+	/// otherwise the opposite direction if it fits, otherwise the roomier side with a scroll bar.
+	/// </summary>
+	[NotInParallel(nameof(AutomationRunner.ShowWindowAndExecuteTests))]
+	public class PopupDirectionFlipTests
+	{
+		private const string PopupName = "_OpenMenuContents";
+		private const string ContentName = "_topToBottom";
+
+		[Test]
+		public async Task FitsAboveButNotBelowOpensUpWithoutScroll()
+		{
+			var (systemWindow, dropDown) = OpenDropDown(itemCount: 2, itemHeight: 50, anchorBottom: 60, direction: Direction.Down);
+
+			var popup = FindPopup(systemWindow);
+			var content = FindContent(popup);
+
+			// It did not fit below (60 of space for a ~100 tall list) but fits easily above
+			await Assert.That(popup.Height).IsEqualTo(content.Height).Within(0.001);
+			await Assert.That(popup.Position.Y).IsEqualTo(dropDown.Position.Y + dropDown.Height).Within(0.001);
+		}
+
+		[Test]
+		public async Task FitsBelowOpensDown()
+		{
+			var (systemWindow, dropDown) = OpenDropDown(itemCount: 2, itemHeight: 50, anchorBottom: 200, direction: Direction.Down);
+
+			var popup = FindPopup(systemWindow);
+			var content = FindContent(popup);
+
+			await Assert.That(popup.Height).IsEqualTo(content.Height).Within(0.001);
+
+			// Opening down puts the top of the popup at the bottom of the anchor
+			await Assert.That(popup.Position.Y + popup.Height).IsEqualTo(dropDown.Position.Y).Within(0.001);
+		}
+
+		[Test]
+		public async Task FitsNeitherSideOpensTowardTheLargerSideWithScroll()
+		{
+			// 5 x 50 = ~250 tall in a 300 tall window - 140 below the anchor, ~134 above it
+			var (systemWindow, dropDown) = OpenDropDown(itemCount: 5, itemHeight: 50, anchorBottom: 140, direction: Direction.Down);
+
+			var popup = FindPopup(systemWindow);
+			var content = FindContent(popup);
+
+			await Assert.That(popup.Height).IsLessThan(content.Height);
+			await Assert.That(popup.Height).IsEqualTo(dropDown.Position.Y - 5).Within(0.001);
+
+			// Below is the roomier side, so it stays open downward
+			await Assert.That(popup.Position.Y + popup.Height).IsEqualTo(dropDown.Position.Y).Within(0.001);
+		}
+
+		[Test]
+		public async Task UpPreferredButOnlyFitsBelowFlipsDown()
+		{
+			var (systemWindow, dropDown) = OpenDropDown(itemCount: 2, itemHeight: 50, anchorBottom: 210, direction: Direction.Up);
+
+			var popup = FindPopup(systemWindow);
+			var content = FindContent(popup);
+
+			await Assert.That(popup.Height).IsEqualTo(content.Height).Within(0.001);
+			await Assert.That(popup.Position.Y + popup.Height).IsEqualTo(dropDown.Position.Y).Within(0.001);
+			await Assert.That(popup.Position.Y).IsGreaterThanOrEqualTo(0);
+		}
+
+		private static (SystemWindow systemWindow, DropDownList dropDown) OpenDropDown(int itemCount, double itemHeight, double anchorBottom, Direction direction)
+		{
+			var systemWindow = new SystemWindow(400, 300);
+
+			var dropDown = new DropDownList("no selection", Color.Black, direction)
+			{
+				Name = "dropDown",
+			};
+
+			for (int i = 0; i < itemCount; i++)
+			{
+				var item = dropDown.AddItem($"Item {i}");
+				item.MinimumSize = new Vector2(150, itemHeight);
+			}
+
+			systemWindow.AddChild(dropDown);
+			dropDown.Position = new Vector2(10, anchorBottom);
+
+			dropDown.InvokeClick();
+
+			return (systemWindow, dropDown);
+		}
+
+		private static GuiWidget FindPopup(SystemWindow systemWindow)
+		{
+			return systemWindow.Descendants<GuiWidget>().First(w => w.Name == PopupName);
+		}
+
+		private static GuiWidget FindContent(GuiWidget popup)
+		{
+			return popup.Descendants<GuiWidget>().First(w => w.Name == ContentName);
+		}
+	}
+}