automatically set TreatSizeAsMaximum for height-based scrolling panels

CHANGELOG.md

@@ -28,6 +28,12 @@ Additions
 - Added the ability to set the anchor that should be used when a tooltip attaches to an element or the mouse
 - Added the ability to display tooltips using the auto-nav style even when using the mouse
 
+Improvements
+- Allow scrolling panels to set height based on children by setting TreatSizeAsMaximum
+
+Fixes
+- Fixed hidden scroll bars inhibiting scrolling on their parent panel
+
 ## 6.3.1
 
 No code changes

Demos/UiDemo.cs

@@ -223,14 +223,15 @@ namespace Demos {
                 PositionOffset = new Vector2(0, 1)
             });
 
-            var subPanel = this.root.AddChild(new Panel(Anchor.AutoLeft, new Vector2(1, 25), Vector2.Zero, false, true) {
-                PositionOffset = new Vector2(0, 1),
+            this.root.AddChild(new VerticalSpace(3));
+            var dynamicSubPanel = this.root.AddChild(new Panel(Anchor.AutoLeft, new Vector2(1, 50), Vector2.Zero, true, true) {
                 Texture = null,
                 ChildPadding = Padding.Empty
             });
-            subPanel.AddChild(new Paragraph(Anchor.AutoLeft, 1, "This is a nested scrolling panel!"));
-            for (var i = 1; i <= 5; i++)
-                subPanel.AddChild(new Button(Anchor.AutoLeft, new Vector2(1, 10), $"Button {i}") {PositionOffset = new Vector2(0, 1)});
+            dynamicSubPanel.AddChild(new Paragraph(Anchor.AutoLeft, 1, "This is a dynamic height nested panel with a maximum height, at which point it starts displaying a scroll bar instead!"));
+            dynamicSubPanel.AddChild(new Button(Anchor.AutoLeft, new Vector2(1, 10), "Press to add more") {
+                OnPressed = _ => dynamicSubPanel.AddChild(new Button(Anchor.AutoLeft, new Vector2(1, 10), "I do nothing"))
+            });
 
             const string alignText = "Paragraphs can have <l Left>left</l> aligned text, <l Right>right</l> aligned text and <l Center>center</l> aligned text.";
             this.root.AddChild(new VerticalSpace(3));

MLEM.Ui/Elements/Panel.cs

@@ -78,6 +78,7 @@ namespace MLEM.Ui.Elements {
         public Panel(Anchor anchor, Vector2 size, Vector2 positionOffset, bool setHeightBasedOnChildren = false, bool scrollOverflow = false, bool autoHideScrollbar = true) : base(anchor, size) {
             this.PositionOffset = positionOffset;
             this.SetHeightBasedOnChildren = setHeightBasedOnChildren;
+            this.TreatSizeAsMaximum = setHeightBasedOnChildren && scrollOverflow;
             this.scrollOverflow = scrollOverflow;
             this.CanBeSelected = false;
 
@@ -119,8 +120,8 @@ namespace MLEM.Ui.Elements {
         public override void ForceUpdateArea() {
             if (this.scrollOverflow) {
                 // sanity check
-                if (this.SetHeightBasedOnChildren)
-                    throw new NotSupportedException("A panel can't both set height based on children and scroll overflow");
+                if (this.SetHeightBasedOnChildren && !this.TreatSizeAsMaximum)
+                    throw new NotSupportedException("A panel can't both scroll overflow and set height based on children without a maximum");
                 foreach (var child in this.Children) {
                     if (child != this.ScrollBar && !child.Anchor.IsAuto())
                         throw new NotSupportedException($"A panel that handles overflow can't contain non-automatic anchors ({child})");
@@ -295,7 +296,7 @@ namespace MLEM.Ui.Elements {
             if (this.Children.Count > 1) {
                 var highestValidChild = this.Children.FirstOrDefault(c => c != this.ScrollBar && !c.IsHidden);
                 var lowestChild = this.GetLowestChild(c => c != this.ScrollBar && !c.IsHidden, true);
-                childrenHeight = lowestChild.GetTotalCoveredArea(false).Bottom - highestValidChild.Area.Top;
+                childrenHeight = lowestChild.GetTotalCoveredArea(true).Bottom - highestValidChild.UnscrolledArea.Top;
             } else {
                 // if we only have one child (the scroll bar), then the children take up no visual height
                 childrenHeight = 0;

MLEM.Ui/Elements/ScrollBar.cs

@@ -251,7 +251,7 @@ namespace MLEM.Ui.Elements {
             var foundMe = false;
             foreach (var child in this.Parent.GetChildren(regardGrandchildren: true)) {
                 if (foundMe) {
-                    if (child is ScrollBar b && !b.Horizontal && b.IsMousedForScrolling(moused))
+                    if (child is ScrollBar b && !b.IsHidden && !b.Horizontal && b.IsMousedForScrolling(moused))
                         return false;
                 } else if (child == this) {
                     // once we found ourselves, all subsequent children are deeper/older!