From 82b8c0ab49ec25bc1cfd37bb18c1168523467cfd Mon Sep 17 00:00:00 2001
From: Ellpeck <me@ellpeck.de>
Date: Mon, 29 Mar 2021 08:28:49 +0200
Subject: [PATCH] fixed a rare stack overflow where scroll bars could get stuck
 in an auto-hide loop

---
 MLEM.Ui/Elements/Element.cs   | 24 ++++++++++++++----------
 MLEM.Ui/Elements/Panel.cs     |  2 +-
 MLEM.Ui/Elements/ScrollBar.cs |  6 ++++--
 3 files changed, 19 insertions(+), 13 deletions(-)

diff --git a/MLEM.Ui/Elements/Element.cs b/MLEM.Ui/Elements/Element.cs
index 449fe42..86e8615 100644
--- a/MLEM.Ui/Elements/Element.cs
+++ b/MLEM.Ui/Elements/Element.cs
@@ -626,26 +626,30 @@ namespace MLEM.Ui.Elements {
 
                 if (this.Children.Count > 0) {
                     Element foundChild = null;
-                    var autoSize = this.Area.Size;
+                    var autoSize = this.UnscrolledArea.Size;
                     if (this.SetHeightBasedOnChildren) {
                         var lowest = this.GetLowestChild(e => !e.IsHidden);
-                        var newY = lowest?.UnscrolledArea.Bottom - pos.Y + this.ScaledChildPadding.Bottom;
-                        if (newY != null && autoSize.Y != newY) {
-                            autoSize.Y = newY.Value;
-                            foundChild = lowest;
+                        if (lowest != null) {
+                            var newHeight = lowest.UnscrolledArea.Bottom - pos.Y + this.ScaledChildPadding.Bottom;
+                            if (!newHeight.Equals(autoSize.Y, 0.01F)) {
+                                autoSize.Y = newHeight;
+                                foundChild = lowest;
+                            }
                         }
                     }
                     if (this.SetWidthBasedOnChildren) {
                         var rightmost = this.GetRightmostChild(e => !e.IsHidden);
-                        var newX = rightmost?.UnscrolledArea.Right - pos.X + this.ScaledChildPadding.Right;
-                        if (newX != null && autoSize.X != newX) {
-                            autoSize.X = newX.Value;
-                            foundChild = rightmost;
+                        if (rightmost != null) {
+                            var newWidth = rightmost.UnscrolledArea.Right - pos.X + this.ScaledChildPadding.Right;
+                            if (!newWidth.Equals(autoSize.X, 0.01F)) {
+                                autoSize.X = newWidth;
+                                foundChild = rightmost;
+                            }
                         }
                     }
                     if (this.TreatSizeAsMinimum)
                         autoSize = Vector2.Max(autoSize, actualSize);
-                    if (!this.Area.Size.Equals(autoSize, 0.01F)) {
+                    if (foundChild != null) {
                         recursion++;
                         if (recursion >= 16) {
                             throw new ArithmeticException($"The area of {this} with root {this.Root?.Name} has recursively updated too often. Does its child {foundChild} contain any conflicting auto-sizing settings?");
diff --git a/MLEM.Ui/Elements/Panel.cs b/MLEM.Ui/Elements/Panel.cs
index c9bda1a..101444f 100644
--- a/MLEM.Ui/Elements/Panel.cs
+++ b/MLEM.Ui/Elements/Panel.cs
@@ -218,7 +218,7 @@ namespace MLEM.Ui.Elements {
                 return;
             // the "real" first child is the scroll bar, which we want to ignore
             var firstChild = this.Children.First(c => c != this.ScrollBar);
-            var lowestChild = this.GetLowestChild(e => !e.IsHidden);
+            var lowestChild = this.GetLowestChild(c => c != this.ScrollBar && !c.IsHidden);
             // the max value of the scrollbar is the amount of non-scaled pixels taken up by overflowing components
             var childrenHeight = lowestChild.Area.Bottom - firstChild.Area.Top;
             this.ScrollBar.MaxValue = (childrenHeight - this.Area.Height) / this.Scale + this.ChildPadding.Height;
diff --git a/MLEM.Ui/Elements/ScrollBar.cs b/MLEM.Ui/Elements/ScrollBar.cs
index 556cc73..a3b2b06 100644
--- a/MLEM.Ui/Elements/ScrollBar.cs
+++ b/MLEM.Ui/Elements/ScrollBar.cs
@@ -44,8 +44,10 @@ namespace MLEM.Ui.Elements {
                 this.maxValue = Math.Max(0, value);
                 // force current value to be clamped
                 this.CurrentValue = this.CurrentValue;
-                if (this.AutoHideWhenEmpty && this.IsHidden != this.maxValue <= 0) {
-                    this.IsHidden = this.maxValue <= 0;
+                // auto-hide if necessary
+                var shouldHide = this.maxValue <= 0.01F;
+                if (this.AutoHideWhenEmpty && this.IsHidden != shouldHide) {
+                    this.IsHidden = shouldHide;
                     this.OnAutoHide?.Invoke(this);
                 }
             }