Draw Invisible Characters From Configuration (#103)

### Description

Adds the ability for developers to pass in an object to determine invisible character drawing.

This is intentionally not doing the character matching and replacement styling in this package. To achieve the flexibility we want, I've raised that to the level of the source editor which can for instance determine if we want to draw a dot with larger emphasis because it's on a tab stop.

#### Detailed changes:
- Moved all line fragment drawing to a new object `LineFragmentRenderer`. Line fragments were increasingly requiring more and more objects to be passed to them. This object centralizes those dependencies into one object.
- Adds a new `InvisibleCharactersDelegate` protocol for API consumers to conform to. Consumers can provide a set of characters to match on, and a method to provide a 'style' to draw them with.
- Makes a slight adjustment to how cursors and line fragment views are added to the view hierarchy.
  - Cursors are now placed at the top of the subview stack, ensuring they're always on top of the content.
  - Line fragments are now placed on the bottom of the subview stack, ensuring they're always drawn under cursors.

### Related Issues

* #22 

### Checklist

- [x] I read and understood the [contributing guide](https://github.com/CodeEditApp/CodeEdit/blob/main/CONTRIBUTING.md) as well as the [code of conduct](https://github.com/CodeEditApp/CodeEdit/blob/main/CODE_OF_CONDUCT.md)
- [x] The issues this PR addresses are related to each other
- [x] My changes generate no new warnings
- [x] My code builds and runs on my machine
- [x] My changes are all related to the related issue above
- [x] I documented my code

### Screenshots

Fleshed out example with CESE replacing tabs with arrows, spaces with dots, emphasizing a zero-width space (​), and replacing newlines with the (¬) character.

![Screenshot 2025-06-10 at 10 55 04 AM](https://github.com/user-attachments/assets/409e0cd0-5eb5-4f1d-8755-5a1a222d0169)

Author: thecoolwinter

Sources/CodeEditTextView/InvisibleCharacters/InvisibleCharactersDelegate.swift

@@ -0,0 +1,20 @@
+//
+//  InvisibleCharactersConfig.swift
+//  CodeEditTextView
+//
+//  Created by Khan Winter on 6/9/25.
+//
+
+import Foundation
+import AppKit
+
+public enum InvisibleCharacterStyle: Hashable {
+    case replace(replacementCharacter: String, color: NSColor, font: NSFont)
+    case emphasize(color: NSColor)
+}
+
+public protocol InvisibleCharactersDelegate: AnyObject {
+    var triggerCharacters: Set<UInt16> { get }
+    func invisibleStyleShouldClearCache() -> Bool
+    func invisibleStyle(for character: UInt16, at range: NSRange, lineRange: NSRange) -> InvisibleCharacterStyle?
+}

Sources/CodeEditTextView/TextLayoutManager/TextLayoutManager+Layout.swift

@@ -251,9 +251,9 @@ extension TextLayoutManager {
             renderDelegate?.lineFragmentView(for: lineFragment.data) ?? LineFragmentView()
         }
         view.translatesAutoresizingMaskIntoConstraints = false
-        view.setLineFragment(lineFragment.data)
+        view.setLineFragment(lineFragment.data, renderer: lineFragmentRenderer)
         view.frame.origin = CGPoint(x: edgeInsets.left, y: yPos)
-        layoutView?.addSubview(view)
+        layoutView?.addSubview(view, positioned: .below, relativeTo: nil)
         view.needsDisplay = true
     }
 }

Sources/CodeEditTextView/TextLayoutManager/TextLayoutManager.swift

@@ -66,12 +66,21 @@ public class TextLayoutManager: NSObject {
 
     public let attachments: TextAttachmentManager = TextAttachmentManager()
 
+    public weak var invisibleCharacterDelegate: InvisibleCharactersDelegate? {
+        didSet {
+            lineFragmentRenderer.invisibleCharacterDelegate = invisibleCharacterDelegate
+            layoutView?.needsDisplay = true
+        }
+    }
+
     // MARK: - Internal
 
     weak var textStorage: NSTextStorage?
     var lineStorage: TextLineStorage<TextLine> = TextLineStorage()
     var markedTextManager: MarkedTextManager = MarkedTextManager()
     let viewReuseQueue: ViewReuseQueue<LineFragmentView, LineFragment.ID> = ViewReuseQueue()
+    let lineFragmentRenderer: LineFragmentRenderer
+
     package var visibleLineIds: Set<TextLine.ID> = []
     /// Used to force a complete re-layout using `setNeedsLayout`
     package var needsLayout: Bool = false
@@ -122,14 +131,20 @@ public class TextLayoutManager: NSObject {
         wrapLines: Bool,
         textView: NSView,
         delegate: TextLayoutManagerDelegate?,
-        renderDelegate: TextLayoutManagerRenderDelegate? = nil
+        renderDelegate: TextLayoutManagerRenderDelegate? = nil,
+        invisibleCharacterDelegate: InvisibleCharactersDelegate? = nil
     ) {
         self.textStorage = textStorage
         self.lineHeightMultiplier = lineHeightMultiplier
         self.wrapLines = wrapLines
         self.layoutView = textView
         self.delegate = delegate
         self.renderDelegate = renderDelegate
+        self.lineFragmentRenderer = LineFragmentRenderer(
+            textStorage: textStorage,
+            invisibleCharacterDelegate: invisibleCharacterDelegate
+        )
+        self.invisibleCharacterDelegate = invisibleCharacterDelegate
         super.init()
         prepareTextLines()
         attachments.layoutManager = self
@@ -166,6 +181,7 @@ public class TextLayoutManager: NSObject {
         viewReuseQueue.usedViews.removeAll()
         maxLineWidth = 0
         markedTextManager.removeAll()
+        lineFragmentRenderer.textStorage = textStorage
         prepareTextLines()
         setNeedsLayout()
     }

Sources/CodeEditTextView/TextLine/LineFragment.swift

@@ -47,6 +47,7 @@ public final class LineFragment: Identifiable, Equatable {
     }
 
     public let id = UUID()
+    public let lineRange: NSRange
     public let documentRange: NSRange
     public var contents: [FragmentContent]
     public var width: CGFloat
@@ -60,13 +61,15 @@ public final class LineFragment: Identifiable, Equatable {
     }
 
     init(
+        lineRange: NSRange,
         documentRange: NSRange,
         contents: [FragmentContent],
         width: CGFloat,
         height: CGFloat,
         descent: CGFloat,
         lineHeightMultiplier: CGFloat
     ) {
+        self.lineRange = lineRange
         self.documentRange = documentRange
         self.contents = contents
         self.width = width
@@ -102,52 +105,6 @@ public final class LineFragment: Identifiable, Equatable {
         }
     }
 
-    public func draw(in context: CGContext, yPos: CGFloat) {
-        context.saveGState()
-
-        // Removes jagged edges
-        context.setAllowsAntialiasing(true)
-        context.setShouldAntialias(true)
-
-        // Effectively increases the screen resolution by drawing text in each LED color pixel (R, G, or B), rather than
-        // the triplet of pixels (RGB) for a regular pixel. This can increase text clarity, but loses effectiveness
-        // in low-contrast settings.
-        context.setAllowsFontSubpixelPositioning(true)
-        context.setShouldSubpixelPositionFonts(true)
-
-        // Quantizes the position of each glyph, resulting in slightly less accurate positioning, and gaining higher
-        // quality bitmaps and performance.
-        context.setAllowsFontSubpixelQuantization(true)
-        context.setShouldSubpixelQuantizeFonts(true)
-
-        ContextSetHiddenSmoothingStyle(context, 16)
-
-        context.textMatrix = .init(scaleX: 1, y: -1)
-
-        var currentPosition: CGFloat = 0.0
-        var currentLocation = 0
-        for content in contents {
-            context.saveGState()
-            switch content.data {
-            case .text(let ctLine):
-                context.textPosition = CGPoint(
-                    x: currentPosition,
-                    y: yPos + height - descent + (heightDifference/2)
-                ).pixelAligned
-                CTLineDraw(ctLine, context)
-            case .attachment(let attachment):
-                attachment.attachment.draw(
-                    in: context,
-                    rect: NSRect(x: currentPosition, y: yPos, width: attachment.width, height: scaledHeight)
-                )
-            }
-            context.restoreGState()
-            currentPosition += content.width
-            currentLocation += content.length
-        }
-        context.restoreGState()
-    }
-
     package func findContent(at location: Int) -> (content: FragmentContent, position: ContentPosition)? {
         var position = ContentPosition(xPos: 0, offset: 0)