Optimize insertion point rendering by reusing views and fixing layout issues

Reuse existing STInsertionPointView instances to avoid unnecessary allocations
when drawing multiple insertion points. Ensure correct sizing of text insertion
indicators by overriding setFrameSize and disabling reliance on
autoresizingMask. Improve blink control behavior for both modern and legacy
indicators.

Author: krzyzanowskim

Sources/STTextViewAppKit/STInsertionPointView.swift

@@ -10,7 +10,7 @@ import AppKit
 ///      |---textInsertionIndicator (STInsertionPointIndicatorProtocol)
 ///
 internal class STInsertionPointView: NSView {
-    private var textInsertionIndicator: any STInsertionPointIndicatorProtocol
+    private let textInsertionIndicator: any STInsertionPointIndicatorProtocol
 
     override var isFlipped: Bool {
         true
@@ -37,6 +37,13 @@ internal class STInsertionPointView: NSView {
         addSubview(textInsertionIndicator)
     }
 
+    override func setFrameSize(_ newSize: NSSize) {
+        super.setFrameSize(newSize)
+        // Manually reset size because `NSTextInsertionIndicator`
+        // does not react to its autoresizingMask
+        textInsertionIndicator.frame.size = newSize
+    }
+
     func blinkStart() {
         textInsertionIndicator.blinkStart()
     }

Sources/STTextViewAppKit/STTextView+InsertionPoint.swift

@@ -89,34 +89,50 @@ extension STTextView {
                 }
             }
 
-            removeInsertionPointView()
+            var existingViews = contentView.subviews.filter { view in
+                type(of: view) == STInsertionPointView.self
+            }
 
             for selectionFrame in textSelectionFrames where !selectionFrame.isNull && !selectionFrame.isInfinite {
                 let insertionViewFrame = CGRect(origin: selectionFrame.origin, size: CGSize(width: max(2, selectionFrame.width), height: selectionFrame.height)).pixelAligned
-
-                var textInsertionIndicator: any STInsertionPointIndicatorProtocol
-                if let customTextInsertionIndicator = self.delegateProxy.textViewInsertionPointView(self, frame: CGRect(origin: .zero, size: insertionViewFrame.size)) {
-                    textInsertionIndicator = customTextInsertionIndicator
+                let insertionView: STInsertionPointView
+                // re-use existing insertion views
+                if !existingViews.isEmpty {
+                    // reuse existing insertion view
+                    insertionView = existingViews.removeFirst() as! STInsertionPointView
+                    insertionView.frame = insertionViewFrame
                 } else {
-                    if #available(macOS 14, *) {
-                        textInsertionIndicator = STTextInsertionIndicatorNew(frame: CGRect(origin: .zero, size: insertionViewFrame.size))
+                    // add new views that exedes existing views
+                    var textInsertionIndicator: any STInsertionPointIndicatorProtocol
+                    if let customTextInsertionIndicator = self.delegateProxy.textViewInsertionPointView(self, frame: CGRect(origin: .zero, size: insertionViewFrame.size)) {
+                        textInsertionIndicator = customTextInsertionIndicator
                     } else {
-                        textInsertionIndicator = STTextInsertionIndicatorOld(frame: CGRect(origin: .zero, size: insertionViewFrame.size))
+                        if #available(macOS 14, *) {
+                            textInsertionIndicator = STTextInsertionIndicatorNew(frame: CGRect(origin: .zero, size: insertionViewFrame.size))
+                        } else {
+                            textInsertionIndicator = STTextInsertionIndicatorOld(frame: CGRect(origin: .zero, size: insertionViewFrame.size))
+                        }
                     }
-                }
 
-                let insertionView = STInsertionPointView(frame: insertionViewFrame, textInsertionIndicator: textInsertionIndicator)
-                insertionView.clipsToBounds = false
-                insertionView.insertionPointColor = insertionPointColor
+                    insertionView = STInsertionPointView(frame: insertionViewFrame, textInsertionIndicator: textInsertionIndicator)
+                    insertionView.clipsToBounds = false
+                    insertionView.insertionPointColor = insertionPointColor
+                    contentView.addSubview(insertionView)
+                }
 
                 if isFirstResponder {
                     insertionView.blinkStart()
                 } else {
                     insertionView.blinkStop()
                 }
+            }
 
-                contentView.addSubview(insertionView)
+            // remove unused insertion points (unused)
+            for v in existingViews {
+                v.removeFromSuperview()
             }
+            existingViews.removeAll()
+
         } else if !shouldDrawInsertionPoint {
             removeInsertionPointView()
         }
@@ -132,9 +148,12 @@ extension STTextView {
 
 @available(macOS 14.0, *)
 private class STTextInsertionIndicatorNew: NSTextInsertionIndicator, STInsertionPointIndicatorProtocol {
+    // NSTextInsertionIndicator start as visible (blinking)
+    private var _isVisible: Bool = true
 
     override init(frame frameRect: CGRect) {
         super.init(frame: frameRect)
+        autoresizingMask = [.width, .height]
     }
 
     @available(*, unavailable)
@@ -153,11 +172,17 @@ private class STTextInsertionIndicatorNew: NSTextInsertionIndicator, STInsertion
     }
 
     func blinkStart() {
-        displayMode = .automatic
+        if !_isVisible {
+            _isVisible = true
+            displayMode = .automatic
+        }
     }
 
     func blinkStop() {
-        displayMode = .hidden
+        if _isVisible {
+            _isVisible = false
+            displayMode = .hidden
+        }
     }
 
     open override var isFlipped: Bool {
@@ -180,6 +205,7 @@ private class STTextInsertionIndicatorOld: NSView, STInsertionPointIndicatorProt
         wantsLayer = true
         layer?.backgroundColor = insertionPointColor.cgColor
         layer?.cornerRadius = 1
+        autoresizingMask = [.width, .height]
     }
 
     @available(*, unavailable)