Allow specifying start and end indices when drawing a TokenizedString or Paragraph

CHANGELOG.md

@@ -22,6 +22,7 @@ Improvements
 - Increased TextFormatter macro recursion limit to 64
 - Allow changing the default values used by default TextFormatter codes
 - Allow setting ExternalGestureHandling through the InputHandler constructor
+- Allow specifying start and end indices when drawing a TokenizedString
 
 Fixes
 - Fixed control characters being included in TextInput
@@ -40,6 +41,7 @@ Additions
 Improvements
 - Increased Element area calculation recursion limit to 64
 - Improved the SquishingGroup algorithm by prioritizing each element's final size
+- Allow specifying start and end indices when drawing a Paragraph
 
 Fixes
 - Fixed images not updating their hidden state properly when the displayed texture changes

Demos/TextFormattingDemo.cs

@@ -34,6 +34,8 @@ namespace Demos {
                 return TextFormattingDemo.DefaultScale * Math.Min(viewport.Width / 1280F, viewport.Height / 720F);
             }
         }
+        private int startIndex;
+        private int endIndex;
 
         public TextFormattingDemo(MlemGame game) : base(game) {}
 
@@ -60,6 +62,7 @@ namespace Demos {
             // we specify our text alignment here too, so that all data is cached correctly for display
             this.tokenizedText = this.formatter.Tokenize(this.font, TextFormattingDemo.Text, TextAlignment.Center);
             this.tokenizedText.Split(this.font, this.GraphicsDevice.Viewport.Width * TextFormattingDemo.WidthMultiplier, this.Scale, TextAlignment.Center);
+            this.endIndex = this.tokenizedText.String.Length;
         }
 
         public override void DoDraw(GameTime time) {
@@ -81,8 +84,8 @@ namespace Demos {
                 }
             }
 
-            // draw the text itself
+            // draw the text itself (start and end indices are optional)
-            this.tokenizedText.Draw(time, this.SpriteBatch, pos, this.font, Color.White, this.Scale, 0);
+            this.tokenizedText.Draw(time, this.SpriteBatch, pos, this.font, Color.White, this.Scale, 0, this.startIndex, this.endIndex);
 
             this.SpriteBatch.End();
         }
@@ -90,8 +93,18 @@ namespace Demos {
         public override void Update(GameTime time) {
             // update our tokenized string to animate the animation codes
             this.tokenizedText.Update(time);
+
+            // change some demo showcase info based on keybinds
             if (this.InputHandler.IsPressed(Keys.B))
                 this.drawBounds = !this.drawBounds;
+            if (this.startIndex > 0 && this.InputHandler.IsDown(Keys.Left))
+                this.startIndex--;
+            if (this.startIndex < this.tokenizedText.String.Length && this.InputHandler.IsDown(Keys.Right))
+                this.startIndex++;
+            if (this.endIndex > 0 && this.InputHandler.IsDown(Keys.Down))
+                this.endIndex--;
+            if (this.endIndex < this.tokenizedText.String.Length && this.InputHandler.IsDown(Keys.Up))
+                this.endIndex++;
         }
 
         public override void Clear() {

MLEM.Ui/Elements/Paragraph.cs

@@ -139,6 +139,16 @@ namespace MLEM.Ui.Elements {
                 this.SetTextDirty();
             }
         }
+        /// <summary>
+        /// The inclusive index in this paragraph's <see cref="Text"/> to start drawing at.
+        /// This value is passed to <see cref="TokenizedString.Draw"/>.
+        /// </summary>
+        public int? DrawStartIndex;
+        /// <summary>
+        /// The exclusive index in this paragraph's <see cref="Text"/> to stop drawing at.
+        /// This value is passed to <see cref="TokenizedString.Draw"/>.
+        /// </summary>
+        public int? DrawEndIndex;
 
         /// <inheritdoc />
         public override bool IsHidden => base.IsHidden || string.IsNullOrWhiteSpace(this.Text);
@@ -206,7 +216,7 @@ namespace MLEM.Ui.Elements {
             var pos = this.DisplayArea.Location + new Vector2(this.GetAlignmentOffset(), 0);
             var sc = this.TextScale * this.TextScaleMultiplier * this.Scale;
             var color = this.TextColor.OrDefault(Color.White) * alpha;
-            this.TokenizedText.Draw(time, batch, pos, this.RegularFont, color, sc, 0);
+            this.TokenizedText.Draw(time, batch, pos, this.RegularFont, color, sc, 0, this.DrawStartIndex, this.DrawEndIndex);
             base.Draw(time, batch, alpha, context);
         }
 

MLEM/Formatting/TokenizedString.cs

@@ -189,29 +189,37 @@ namespace MLEM.Formatting {
         }
 
         /// <inheritdoc cref="GenericFont.DrawString(SpriteBatch,string,Vector2,Color,float,Vector2,float,SpriteEffects,float)"/>
-        public void Draw(GameTime time, SpriteBatch batch, Vector2 pos, GenericFont font, Color color, float scale, float depth) {
+        public void Draw(GameTime time, SpriteBatch batch, Vector2 pos, GenericFont font, Color color, float scale, float depth, int? startIndex = null, int? endIndex = null) {
             var innerOffset = new Vector2(this.initialInnerOffset * scale, 0);
             for (var t = 0; t < this.Tokens.Length; t++) {
                 var token = this.Tokens[t];
+                if (endIndex != null && token.Index >= endIndex)
+                    return;
+
                 var drawFont = token.GetFont(font);
                 var drawColor = token.GetColor(color);
 
+                if (startIndex == null || token.Index >= startIndex)
                     token.DrawSelf(time, batch, pos + innerOffset, drawFont, drawColor, scale, depth);
                 innerOffset.X += token.GetSelfWidth(drawFont) * scale;
 
                 var indexInToken = 0;
                 for (var l = 0; l < token.SplitDisplayString.Length; l++) {
-                    var charIndex = 0;
+                    var cpsIndex = 0;
                     var line = new CodePointSource(token.SplitDisplayString[l]);
-                    while (charIndex < line.Length) {
+                    while (cpsIndex < line.Length) {
-                        var (codePoint, length) = line.GetCodePoint(charIndex);
+                        if (endIndex != null && token.Index + indexInToken >= endIndex)
+                            return;
+
+                        var (codePoint, length) = line.GetCodePoint(cpsIndex);
                         var character = CodePointSource.ToString(codePoint);
 
+                        if (startIndex == null || token.Index + indexInToken >= startIndex)
                             token.DrawCharacter(time, batch, codePoint, character, indexInToken, pos + innerOffset, drawFont, drawColor, scale, depth);
 
                         innerOffset.X += drawFont.MeasureString(character).X * scale;
-                        charIndex += length;
+                        indexInToken += length;
-                        indexInToken++;
+                        cpsIndex += length;
                     }
 
                     // only split at a new line, not between tokens!