three tiny fixes

Docs/articles/ui.md

@@ -13,7 +13,7 @@ protected override void LoadContent() {
     // Load your other content here
 
     // Initialize the Ui system
-    this.UiSystem = new UiSystem(this.Window, this.GraphicsDevice, new UntexturedStyle(this.SpriteBatch));
+    this.UiSystem = new UiSystem(this, this.GraphicsDevice, new UntexturedStyle(this.SpriteBatch));
 }
 
 protected override void Update(GameTime gameTime) {

MLEM.Ui/Elements/Group.cs

@@ -6,6 +6,7 @@ namespace MLEM.Ui.Elements {
     /// <summary>
     /// A group element to be used inside of a <see cref="UiSystem"/>.
     /// A group is an element that has no rendering or interaction on its own, but that can aid with automatic placement of child elements.
+    /// If a grouping whose children scroll, and which has a <see cref="ScrollBar"/>, is desired, a <see cref="Panel"/> with its <see cref="Panel.Texture"/> set to <see langword="null"/> can be used.
     /// </summary>
     public class Group : Element {
 

MLEM.Ui/Elements/Panel.cs

@@ -13,6 +13,7 @@ namespace MLEM.Ui.Elements {
     /// A panel element to be used inside of a <see cref="UiSystem"/>.
     /// The panel is a complex element that displays a box as a background to all of its child elements.
     /// Additionally, a panel can be set to scroll overflowing elements on construction, which causes all elements that don't fit into the panel to be hidden until scrolled to using a <see cref="ScrollBar"/>.
+    /// If an element similar to a <see cref="Group"/>, but with scrolling content, is desired, a panel with its <see cref="Texture"/> set to <see langword="null"/> can be used.
     /// </summary>
     public class Panel : Element {
 
@@ -24,7 +25,8 @@ namespace MLEM.Ui.Elements {
         public readonly ScrollBar ScrollBar;
 
         /// <summary>
-        /// The texture that this panel should have, or null if it should be invisible.
+        /// The texture that this panel should have.
+        /// If this is set to <see langword="null"/>, this panel will not have a texture, but all of its content will still be visible.
         /// </summary>
         public StyleProp<NinePatch> Texture;
         /// <summary>
@@ -64,6 +66,7 @@ namespace MLEM.Ui.Elements {
         private StyleProp<float> scrollBarOffset;
         private float lastScrollOffset;
         private bool childrenDirtyForScroll;
+        private bool scrollBarMaxHistoryDirty;
 
         /// <summary>
         /// Creates a new panel with the given settings.
@@ -83,6 +86,7 @@ namespace MLEM.Ui.Elements {
 
             if (scrollOverflow) {
                 this.scrollBarMaxHistory = new float[3];
+                this.scrollBarMaxHistoryDirty = true;
                 this.ResetScrollBarMaxHistory();
 
                 this.ScrollBar = new ScrollBar(Anchor.TopRight, Vector2.Zero, 0, 0) {
@@ -172,6 +176,14 @@ namespace MLEM.Ui.Elements {
             base.RemoveChildren(e => e != this.ScrollBar && (condition == null || condition(e)));
         }
 
+        /// <inheritdoc />
+        public override void Update(GameTime time) {
+            // reset the scroll bar's max history when an update happens, at which point we know that any scroll bar recursion has "settled"
+            // (this reset ensures that the max history is recursion-internal and old values aren't reused when elements get modified later)
+            this.ResetScrollBarMaxHistory();
+            base.Update(time);
+        }
+
         /// <inheritdoc />
         public override void Draw(GameTime time, SpriteBatch batch, float alpha, SpriteBatchContext context) {
             // draw children onto the render target if we have one
@@ -334,6 +346,7 @@ namespace MLEM.Ui.Elements {
                 this.scrollBarMaxHistory[0] = this.scrollBarMaxHistory[1];
                 this.scrollBarMaxHistory[1] = this.scrollBarMaxHistory[2];
                 this.scrollBarMaxHistory[2] = scrollBarMax;
+                this.scrollBarMaxHistoryDirty = true;
 
                 this.ScrollBar.MaxValue = scrollBarMax;
                 this.relevantChildrenDirty = true;
@@ -419,9 +432,10 @@ namespace MLEM.Ui.Elements {
         }
 
         private void ResetScrollBarMaxHistory() {
-            if (this.scrollOverflow) {
+            if (this.scrollOverflow && this.scrollBarMaxHistoryDirty) {
                 for (var i = 0; i < this.scrollBarMaxHistory.Length; i++)
                     this.scrollBarMaxHistory[i] = -1;
+                this.scrollBarMaxHistoryDirty = false;
             }
         }