From 2e8b311b007aefd99b560c94ccf5001f156e4530 Mon Sep 17 00:00:00 2001
From: Ellpeck <megamaximal@gmail.com>
Date: Sun, 11 Aug 2019 00:39:40 +0200
Subject: [PATCH] made text fields auto-scroll once they're too full

---
 MLEM.Ui/Elements/TextField.cs           | 21 +++++++++++++++++++--
 Tests/Content/Fonts/TestFont.spritefont |  4 ++--
 2 files changed, 21 insertions(+), 4 deletions(-)

diff --git a/MLEM.Ui/Elements/TextField.cs b/MLEM.Ui/Elements/TextField.cs
index b012b1b..8149a67 100644
--- a/MLEM.Ui/Elements/TextField.cs
+++ b/MLEM.Ui/Elements/TextField.cs
@@ -20,6 +20,7 @@ namespace MLEM.Ui.Elements {
         public float TextOffsetX = 4;
         private IGenericFont font;
         private double caretBlinkTimer;
+        private int textStartIndex;
 
         public TextField(Anchor anchor, Vector2 size, IGenericFont font = null) : base(anchor, size) {
             this.font = font;
@@ -38,8 +39,23 @@ namespace MLEM.Ui.Elements {
                         textChanged = true;
                     }
                 }
-                if (textChanged)
+                if (textChanged) {
+                    var length = this.font.MeasureString(this.Text).X * this.TextScale;
+                    var maxWidth = this.DisplayArea.Width - this.TextOffsetX * 2;
+                    if (length > maxWidth) {
+                        for (var i = Math.Max(0, this.textStartIndex - 1); i < this.Text.Length; i++) {
+                            var substring = this.Text.ToString(i, this.Text.Length - i);
+                            if (this.font.MeasureString(substring).X * this.TextScale <= maxWidth) {
+                                this.textStartIndex = i;
+                                break;
+                            }
+                        }
+                    } else {
+                        this.textStartIndex = 0;
+                    }
+
                     this.OnTextChange?.Invoke(this, this.Text.ToString());
+                }
             };
         }
 
@@ -61,7 +77,8 @@ namespace MLEM.Ui.Elements {
             }
             batch.Draw(tex, this.DisplayArea, color);
             var caret = this.IsSelected && this.caretBlinkTimer >= 0.5F ? "|" : "";
-            this.font.DrawCenteredString(batch, this.Text + caret, this.DisplayArea.Location.ToVector2() + new Vector2(this.TextOffsetX, this.DisplayArea.Height / 2), this.TextScale, Color.White * alpha, false, true);
+            var text = this.Text.ToString(this.textStartIndex, this.Text.Length - this.textStartIndex) + caret;
+            this.font.DrawCenteredString(batch, text, this.DisplayArea.Location.ToVector2() + new Vector2(this.TextOffsetX, this.DisplayArea.Height / 2), this.TextScale, Color.White * alpha, false, true);
             base.Draw(time, batch, alpha);
         }
 
diff --git a/Tests/Content/Fonts/TestFont.spritefont b/Tests/Content/Fonts/TestFont.spritefont
index b31c317..de8e2fe 100644
--- a/Tests/Content/Fonts/TestFont.spritefont
+++ b/Tests/Content/Fonts/TestFont.spritefont
@@ -11,7 +11,7 @@ with.
     <!--
     Modify this string to change the font that will be imported.
     -->
-    <FontName>BitPotion</FontName>
+    <FontName>BitPotionExt</FontName>
 
     <!--
     Size is a float value, measured in points. Modify this value to change
@@ -41,7 +41,7 @@ with.
     If you uncomment this line, the default character will be substituted if you draw
     or measure text that contains characters which were not included in the font.
     -->
-    <!-- <DefaultCharacter>*</DefaultCharacter> -->
+    <DefaultCharacter>*</DefaultCharacter>
 
     <!--
     CharacterRegions control what letters are available in the font. Every