From c28f6d858c624220d17b4c741409c51788626feb Mon Sep 17 00:00:00 2001
From: Ellpeck <me@ellpeck.de>
Date: Sun, 9 Jan 2022 01:12:16 +0100
Subject: [PATCH] Ensure that a panel gets notified of all relevant changes by
 calling OnChildAreaDirty for all grandchildren

---
 CHANGELOG.md                       |  1 +
 MLEM.Ui/Elements/Element.cs        | 16 ++++++++++------
 MLEM.Ui/Elements/Panel.cs          |  9 +++++++++
 MLEM.Ui/Elements/Paragraph.cs      |  4 ++--
 MLEM.Ui/Elements/SquishingGroup.cs |  7 ++++---
 5 files changed, 26 insertions(+), 11 deletions(-)

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 013af60..3a9031d 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -24,6 +24,7 @@ Fixes
 Improvements
 - Allow for checkboxes and radio buttons to be disabled
 - Only set a paragraph's area dirty when a text change would cause it to change size
+- Ensure that a panel gets notified of all relevant changes by calling OnChildAreaDirty for all grandchildren
 
 Fixes
 - Fixed paragraph links having incorrect hover locations when using special text alignments
diff --git a/MLEM.Ui/Elements/Element.cs b/MLEM.Ui/Elements/Element.cs
index f386e39..ab0bd07 100644
--- a/MLEM.Ui/Elements/Element.cs
+++ b/MLEM.Ui/Elements/Element.cs
@@ -530,7 +530,7 @@ namespace MLEM.Ui.Elements {
         /// </summary>
         public void SetAreaDirty() {
             this.AreaDirty = true;
-            this.Parent?.OnChildAreaDirty(this);
+            this.Parent?.OnChildAreaDirty(this, false);
         }
 
         /// <summary>
@@ -1061,13 +1061,17 @@ namespace MLEM.Ui.Elements {
         }
 
         /// <summary>
-        /// A method that gets called by this element's <see cref="Children"/> when their <see cref="SetAreaDirty"/> methods get called.
+        /// A method that gets called by this element's <see cref="Children"/> or any of its grandchildren when their <see cref="SetAreaDirty"/> methods get called.
         /// Note that the element's area might already be dirty, which will not stop this method from being called.
         /// </summary>
-        /// <param name="child">The child whose area is being set dirty</param>
-        protected virtual void OnChildAreaDirty(Element child) {
-            if (child.Anchor >= Anchor.AutoLeft || this.SetWidthBasedOnChildren || this.SetHeightBasedOnChildren)
-                this.SetAreaDirty();
+        /// <param name="child">The child whose area is being set dirty.</param>
+        /// <param name="grandchild">Whether the <paramref name="child"/> is a grandchild of this element, rather than a direct child.</param>
+        protected virtual void OnChildAreaDirty(Element child, bool grandchild) {
+            if (!grandchild) {
+                if (child.Anchor >= Anchor.AutoLeft || this.SetWidthBasedOnChildren || this.SetHeightBasedOnChildren)
+                    this.SetAreaDirty();
+            }
+            this.Parent?.OnChildAreaDirty(child, true);
         }
 
         /// <summary>
diff --git a/MLEM.Ui/Elements/Panel.cs b/MLEM.Ui/Elements/Panel.cs
index b84e9cf..39bf5a3 100644
--- a/MLEM.Ui/Elements/Panel.cs
+++ b/MLEM.Ui/Elements/Panel.cs
@@ -157,6 +157,15 @@ namespace MLEM.Ui.Elements {
             return relevant;
         }
 
+        /// <inheritdoc />
+        protected override void OnChildAreaDirty(Element child, bool grandchild) {
+            base.OnChildAreaDirty(child, grandchild);
+            // we only need to scroll when a grandchild changes, since all of our children are forced 
+            // to be auto-anchored and so will automatically propagate their changes up to us
+            if (grandchild)
+                this.ScrollChildren();
+        }
+
         /// <inheritdoc />
         public override void Draw(GameTime time, SpriteBatch batch, float alpha, BlendState blendState, SamplerState samplerState, DepthStencilState depthStencilState, Effect effect, Matrix matrix) {
             if (this.Texture.HasValue())
diff --git a/MLEM.Ui/Elements/Paragraph.cs b/MLEM.Ui/Elements/Paragraph.cs
index 5c208bf..0784e2b 100644
--- a/MLEM.Ui/Elements/Paragraph.cs
+++ b/MLEM.Ui/Elements/Paragraph.cs
@@ -191,8 +191,8 @@ namespace MLEM.Ui.Elements {
         /// </summary>
         protected void SetTextDirty() {
             this.TokenizedText = null;
-            // only set our area dirty if our size changed as a result of this action or if we have link children we need to update
-            if (!this.AreaDirty && (!this.CalcActualSize(this.ParentArea).Equals(this.DisplayArea.Size, Epsilon) || this.Children.Count > 0))
+            // only set our area dirty if our size changed as a result of this action
+            if (!this.AreaDirty && !this.CalcActualSize(this.ParentArea).Equals(this.DisplayArea.Size, Epsilon))
                 this.SetAreaDirty();
         }
 
diff --git a/MLEM.Ui/Elements/SquishingGroup.cs b/MLEM.Ui/Elements/SquishingGroup.cs
index 46870a3..956b09d 100644
--- a/MLEM.Ui/Elements/SquishingGroup.cs
+++ b/MLEM.Ui/Elements/SquishingGroup.cs
@@ -30,9 +30,10 @@ namespace MLEM.Ui.Elements {
         }
 
         /// <inheritdoc />
-        protected override void OnChildAreaDirty(Element child) {
-            base.OnChildAreaDirty(child);
-            this.SetAreaDirty();
+        protected override void OnChildAreaDirty(Element child, bool grandchild) {
+            base.OnChildAreaDirty(child, grandchild);
+            if (!grandchild)
+                this.SetAreaDirty();
         }
 
         private static bool SquishChild(Element element, out RectangleF squishedArea) {