Add optional Metal GPU-accelerated terminal renderer

Sources/SwiftTerm/Mac/MacTerminalView.swift

@@ -98,6 +98,15 @@ open class TerminalView: NSView, NSTextInputClient, NSUserInterfaceValidations,
     var cellDimension: CellDimension!
     var caretView: CaretView!
     public var terminal: Terminal!
+
+    /// The rendering backend used by this terminal view.
+    /// Set to a ``MetalTerminalRenderer`` instance to enable GPU-accelerated rendering.
+    /// Defaults to ``CoreGraphicsRenderer`` if not set before ``setup()`` completes.
+    public var renderer: TerminalRenderer? {
+        didSet {
+            renderer?.setup(view: self)
+        }
+    }
     private var progressBarView: TerminalProgressBarView?
     private var progressReportTimer: Timer?
     private var lastProgressValue: UInt8?
@@ -175,6 +184,11 @@ open class TerminalView: NSView, NSTextInputClient, NSUserInterfaceValidations,
         setupOptions()
         setupProgressBar()
         setupFocusNotification()
+        if renderer == nil {
+            let cg = CoreGraphicsRenderer()
+            cg.setup(view: self)
+            renderer = cg
+        }
     }
 
     func startDisplayUpdates ()
@@ -534,7 +548,17 @@ open class TerminalView: NSView, NSTextInputClient, NSUserInterfaceValidations,
         guard let currentContext = getCurrentGraphicsContext() else {
             return
         }
-        drawTerminalContents (dirtyRect: dirtyRect, context: currentContext, bufferOffset: terminal.displayBuffer.yDisp)
+        let bufferOffset = terminal.displayBuffer.yDisp
+        if let renderer {
+            let dims = CellDimensions(
+                width: cellDimension.width,
+                height: cellDimension.height,
+                descent: CTFontGetDescent(fontSet.normal),
+                leading: CTFontGetLeading(fontSet.normal))
+            renderer.draw(in: currentContext, dirtyRect: dirtyRect, cellDimensions: dims, bufferOffset: bufferOffset)
+        } else {
+            drawTerminalContents(dirtyRect: dirtyRect, context: currentContext, bufferOffset: bufferOffset)
+        }
     }
 
     public override func cursorUpdate(with event: NSEvent)

Sources/SwiftTerm/Rendering/CoreGraphicsRenderer.swift

@@ -0,0 +1,44 @@
+//
+//  CoreGraphicsRenderer.swift
+//
+//  Default renderer that delegates to the existing CoreGraphics-based
+//  drawing code in AppleTerminalView.
+//
+#if os(macOS) || os(iOS) || os(visionOS)
+import Foundation
+import CoreGraphics
+
+/// A thin wrapper around the existing CoreGraphics rendering in
+/// ``TerminalView``.  It delegates ``draw(in:dirtyRect:cellDimensions:bufferOffset:)``
+/// back to the view's ``drawTerminalContents(dirtyRect:context:bufferOffset:)`` method.
+public class CoreGraphicsRenderer: TerminalRenderer {
+    weak var view: TerminalView?
+
+    public init() {}
+
+    public func setup(view: TerminalView) {
+        self.view = view
+    }
+
+    public func draw(
+        in context: CGContext,
+        dirtyRect: CGRect,
+        cellDimensions: CellDimensions,
+        bufferOffset: Int
+    ) {
+        view?.drawTerminalContents(dirtyRect: dirtyRect, context: context, bufferOffset: bufferOffset)
+    }
+
+    public func colorsChanged() {
+        view?.resetCaches()
+    }
+
+    public func fontChanged() {
+        view?.resetCaches()
+    }
+
+    public func invalidateAll() {
+        view?.resetCaches()
+    }
+}
+#endif