Fixed TextInput not working correctly when using surrogate pairs

CHANGELOG.md

@@ -17,6 +17,9 @@ Jump to version:
 Additions
 - Added GraphicsExtensions.WithRenderTargets, a multi-target version of WithRenderTarget
 
+Fixes
+- Fixed TextInput not working correctly when using surrogate pairs
+
 ## 6.2.0
 
 ### MLEM

MLEM/Font/CodePointSource.cs

@@ -63,6 +63,18 @@ namespace MLEM.Font {
             return (curr, 1);
         }
 
+        /// <summary>
+        /// Returns an index in this code point source that is as close to <paramref name="index"/> as possible, but not between two members of a surrogate pair. If the <paramref name="index"/> is already not between surrogate pairs, it is returned unchanged.
+        /// </summary>
+        /// <param name="index">The index to ensure is not between surrogates.</param>
+        /// <param name="increase">Whether the returned index should be increased by 1 (instead of decreased by 1) when it is between surrogates.</param>
+        /// <returns>An index close to <paramref name="index"/>, but not between surrogates.</returns>
+        public int EnsureSurrogateBoundary(int index, bool increase) {
+            if (index < this.Length && char.IsLowSurrogate(this[index]))
+                return increase && index < this.Length - 1 || index <= 0 ? index + 1 : index - 1;
+            return index;
+        }
+
         /// <summary>Returns an enumerator that iterates through the collection.</summary>
         /// <returns>A <see cref="T:System.Collections.Generic.IEnumerator`1" /> that can be used to iterate through the collection.</returns>
         /// <filterpriority>1</filterpriority>

MLEM/Input/TextInput.cs

@@ -105,7 +105,8 @@ namespace MLEM.Input {
             set {
                 var val = (int) MathHelper.Clamp(value, 0F, this.text.Length);
                 if (this.caretPos != val) {
-                    this.caretPos = val;
+                    // ensure that we don't move to a location that is between high and low surrogates
+                    this.caretPos = new CodePointSource(this.text).EnsureSurrogateBoundary(val, val > this.caretPos);
                     this.caretBlinkTimer = 0;
                     this.SetTextDataDirty(false);
                 }
@@ -360,7 +361,7 @@ namespace MLEM.Input {
             if (!this.FilterText(ref strg, removeMismatching))
                 return;
             if (this.MaximumCharacters != null && strg.Length > this.MaximumCharacters)
-                strg = strg.Substring(0, this.MaximumCharacters.Value);
+                strg = strg.Substring(0, new CodePointSource(strg).EnsureSurrogateBoundary(this.MaximumCharacters.Value, false));
             this.text.Clear();
             this.text.Append(strg);
             this.CaretPos = this.text.Length;
@@ -378,7 +379,7 @@ namespace MLEM.Input {
             if (!this.FilterText(ref strg, removeMismatching))
                 return false;
             if (this.MaximumCharacters != null && this.text.Length + strg.Length > this.MaximumCharacters)
-                strg = strg.Substring(0, this.MaximumCharacters.Value - this.text.Length);
+                strg = strg.Substring(0, new CodePointSource(strg).EnsureSurrogateBoundary(this.MaximumCharacters.Value - this.text.Length, false));
             this.text.Insert(this.CaretPos, strg);
             this.CaretPos += strg.Length;
             this.SetTextDataDirty();
@@ -393,7 +394,8 @@ namespace MLEM.Input {
         public bool RemoveText(int index, int length) {
             if (index < 0 || index >= this.text.Length)
                 return false;
-            this.text.Remove(index, length);
+            var source = new CodePointSource(this.text);
+            this.text.Remove(source.EnsureSurrogateBoundary(index, false), source.EnsureSurrogateBoundary(index + length, true) - index);
             // ensure that caret pos is still in bounds
             this.CaretPos = this.CaretPos;
             this.SetTextDataDirty();