Tint split view divider based on theme background

macos/Ghostty.xcodeproj/project.pbxproj

@@ -65,6 +65,7 @@
 		A5E112952AF73E8A00C6E0C2 /* ClipboardConfirmationController.swift in Sources */ = {isa = PBXBuildFile; fileRef = A5E112942AF73E8A00C6E0C2 /* ClipboardConfirmationController.swift */; };
 		A5E112972AF7401B00C6E0C2 /* ClipboardConfirmationView.swift in Sources */ = {isa = PBXBuildFile; fileRef = A5E112962AF7401B00C6E0C2 /* ClipboardConfirmationView.swift */; };
 		A5FEB3002ABB69450068369E /* main.swift in Sources */ = {isa = PBXBuildFile; fileRef = A5FEB2FF2ABB69450068369E /* main.swift */; };
+		C159E81D2B66A06B00FDFE9C /* NSColor+Extension.swift in Sources */ = {isa = PBXBuildFile; fileRef = C159E81C2B66A06B00FDFE9C /* NSColor+Extension.swift */; };
 /* End PBXBuildFile section */
 
 /* Begin PBXFileReference section */
@@ -123,6 +124,7 @@
 		A5E112942AF73E8A00C6E0C2 /* ClipboardConfirmationController.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = ClipboardConfirmationController.swift; sourceTree = "<group>"; };
 		A5E112962AF7401B00C6E0C2 /* ClipboardConfirmationView.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = ClipboardConfirmationView.swift; sourceTree = "<group>"; };
 		A5FEB2FF2ABB69450068369E /* main.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = main.swift; sourceTree = "<group>"; };
+		C159E81C2B66A06B00FDFE9C /* NSColor+Extension.swift */ = {isa = PBXFileReference; lastKnownFileType = sourcecode.swift; path = "NSColor+Extension.swift"; sourceTree = "<group>"; };
 /* End PBXFileReference section */
 
 /* Begin PBXFrameworksBuildPhase section */
@@ -187,6 +189,7 @@
 				8503D7C62A549C66006CFF3D /* FullScreenHandler.swift */,
 				A59630962AEE163600D64628 /* HostingWindow.swift */,
 				A59FB5D02AE0DEA7009128F3 /* MetalView.swift */,
+				C159E81C2B66A06B00FDFE9C /* NSColor+Extension.swift */,
 				A5CEAFDA29B8005900646FDA /* SplitView */,
 			);
 			path = Helpers;
@@ -489,6 +492,7 @@
 				A5E112952AF73E8A00C6E0C2 /* ClipboardConfirmationController.swift in Sources */,
 				8503D7C72A549C66006CFF3D /* FullScreenHandler.swift in Sources */,
 				A596309E2AEE1D6C00D64628 /* TerminalView.swift in Sources */,
+				C159E81D2B66A06B00FDFE9C /* NSColor+Extension.swift in Sources */,
 				A5CEAFDE29B8058B00646FDA /* SplitView.Divider.swift in Sources */,
 				A5E112972AF7401B00C6E0C2 /* ClipboardConfirmationView.swift in Sources */,
 				A514C8D82B54DC6800493A16 /* Ghostty.App.swift in Sources */,

macos/Sources/Ghostty/Ghostty.App.swift

@@ -30,7 +30,7 @@ extension Ghostty {
         /// The global app configuration. This defines the app level configuration plus any behavior
         /// for new windows, tabs, etc. Note that when creating a new window, it may inherit some
         /// configuration (i.e. font size) from the previously focused window. This would override this.
-        private(set) var config: Config
+        @Published private(set) var config: Config
         
         /// The ghostty app instance. We only have one of these for the entire app, although I guess
         /// in theory you can have multiple... I don't know why you would...

macos/Sources/Helpers/NSColor+Extension.swift

@@ -0,0 +1,21 @@
+//
+//  NSColor+Extension.swift
+//  Ghostty
+//
+//  Created by Pete Schaffner on 28/01/2024.
+//
+
+import AppKit
+
+extension NSColor {
+    var isLightColor: Bool {
+        var r: CGFloat = 0
+        var g: CGFloat = 0
+        var b: CGFloat = 0
+        var a: CGFloat = 0
+
+        self.getRed(&r, green: &g, blue: &b, alpha: &a)
+        let luminance = (0.299 * r) + (0.587 * g) + (0.114 * b)
+        return luminance > 0.5
+    }
+}

macos/Sources/Helpers/SplitView/SplitView.Divider.swift

@@ -3,6 +3,8 @@ import SwiftUI
 extension SplitView {
     /// The split divider that is rendered and can be used to resize a split view.
     struct Divider: View {
+        @EnvironmentObject var ghostty: Ghostty.App
+
         let direction: SplitViewDirection
         let visibleSize: CGFloat
         let invisibleSize: CGFloat
@@ -43,12 +45,20 @@ extension SplitView {
             }
         }
 
+        private var color: Color {
+            let backgroundColor = NSColor(ghostty.config.backgroundColor)
+            let isLightBackground = backgroundColor.isLightColor
+            let newColor = isLightBackground ? backgroundColor.shadow(withLevel: 0.1) : backgroundColor.shadow(withLevel: 0.4)
+
+            return Color(nsColor: newColor ?? .gray.withAlphaComponent(0.5))
+        }
+
         var body: some View {
             ZStack {
                 Color.clear
                     .frame(width: invisibleWidth, height: invisibleHeight)
                 Rectangle()
-                    .fill(Color.gray)
+                    .fill(color)
                     .frame(width: visibleWidth, height: visibleHeight)
             }
             .onHover { isHovered in