Scroll twice as far, with a setting for how far

Sources/CodecCore/Preferences.swift

@@ -38,6 +38,11 @@ public final class Preferences: ObservableObject {
     @Published public var shellPath: String { didSet { store(shellPath, .shellPath) } }
     @Published public var showSystemStats: Bool { didSet { store(showSystemStats, .showSystemStats) } }
     @Published public var prompt: PromptConfiguration { didSet { storePrompt() } }
+    /// How far the trackpad and the mouse wheel scroll, as a multiple of the system's own rate. At 1×,
+    /// SwiftTerm's, the scrollback follows the fingers and a wheel notch moves one line: many swipes to
+    /// get through a long output.
+    @Published public var scrollSpeed: Double { didSet { store(scrollSpeed, .scrollSpeed) } }
+    public static let scrollSpeeds: ClosedRange<Double> = 1...5
     /// Copies text to the clipboard as soon as it's selected.
     @Published public var copyOnSelect: Bool { didSet { store(copyOnSelect, .copyOnSelect) } }
     /// Shows the rest of a matching earlier command, dimmed, as you type (zsh).
@@ -74,7 +79,7 @@ public final class Preferences: ObservableObject {
              codecSounds, paneSounds, soundVolume, optionAsMeta, exitBehavior, shellIntegration, shellPath,
              showSystemStats, prompt, copyOnSelect, suggestCommands, historyKeys, friendlyCompletion, colorFileListings,
              ezaForLs, recordHistory, restoreWindows, restorePaneContents, showUsualDuration, activateVenvs, explainFailures,
-             checkForUpdates, commandSeparators, shadeAlternateCommands
+             checkForUpdates, commandSeparators, shadeAlternateCommands, scrollSpeed
     }
 
     private static let factoryDefaults: [Key: Any] = [
@@ -97,6 +102,7 @@ public final class Preferences: ObservableObject {
         .shellIntegration: true,
         .shellPath: "",
         .showSystemStats: true,
+        .scrollSpeed: 2.0,
         .copyOnSelect: false,
         .suggestCommands: true,
         .historyKeys: true,
@@ -134,6 +140,7 @@ public final class Preferences: ObservableObject {
         shellIntegration = defaults.bool(forKey: Key.shellIntegration.rawValue)
         shellPath = defaults.string(forKey: Key.shellPath.rawValue) ?? ""
         showSystemStats = defaults.bool(forKey: Key.showSystemStats.rawValue)
+        scrollSpeed = Self.clamp(defaults.double(forKey: Key.scrollSpeed.rawValue), Self.scrollSpeeds, fallback: 2)
         copyOnSelect = defaults.bool(forKey: Key.copyOnSelect.rawValue)
         suggestCommands = defaults.bool(forKey: Key.suggestCommands.rawValue)
         historyKeys = defaults.bool(forKey: Key.historyKeys.rawValue)

Sources/CodecUI/Pane.swift

@@ -1439,6 +1439,7 @@ final class Pane: LocalProcessTerminalViewDelegate {
         terminal.selectedTextBackgroundColor = theme.selection
         terminal.installColors(theme.terminalPalette)
         terminal.optionAsMetaKey = preferences.optionAsMeta
+        terminal.scrollSensitivity = CGFloat(preferences.scrollSpeed)
         view.apply(theme: theme, scanlines: preferences.scanlines)
         refreshCommandSeparators()
     }

Sources/CodecUI/SettingsView.swift

@@ -258,6 +258,21 @@ private struct ShellSettings: View {
                 Text("Codec keeps where each command ran, how long it took and whether it failed, alongside your shell’s own history. Commands typed with a leading space aren’t kept. Search it with ⌘Y.")
                     .foregroundStyle(.secondary)
             }
+            Section {
+                LabeledContent("Speed") {
+                    HStack {
+                        Slider(value: $prefs.scrollSpeed, in: Preferences.scrollSpeeds, step: 0.5)
+                        Text(prefs.scrollSpeed.formatted(.number.precision(.fractionLength(0...1))) + "×")
+                            .monospacedDigit()
+                            .frame(width: 44, alignment: .trailing)
+                    }
+                }
+            } header: {
+                Text("Scrolling")
+            } footer: {
+                Text("How far the trackpad and the mouse wheel scroll: at 1× the scrollback follows your fingers and moves a line for each notch of the wheel. Also applies in full-screen programs such as vim and less.")
+                    .foregroundStyle(.secondary)
+            }
             Section {
                 Toggle("Copy text as soon as it’s selected", isOn: $prefs.copyOnSelect)
             } header: {

Tests/CodecCoreTests/PoliciesTests.swift

@@ -77,6 +77,7 @@ struct PreferencesTests {
         #expect(!preferences.scanlines)
         #expect(preferences.commandSeparators)
         #expect(preferences.shadeAlternateCommands)
+        #expect(preferences.scrollSpeed == 2)
     }
 
     @Test func persistsChangesAcrossInstances() {
@@ -88,12 +89,14 @@ struct PreferencesTests {
         first.bell = .codecLock
         first.exitBehavior = .keepOpen
         first.shellPath = "/bin/bash"
+        first.scrollSpeed = 3.5
         let second = Preferences(defaults: defaults)
         #expect(second.themeID == "amber")
         #expect(second.fontSize == 15)
         #expect(second.bell == .codecLock)
         #expect(second.exitBehavior == .keepOpen)
         #expect(second.shellPath == "/bin/bash")
+        #expect(second.scrollSpeed == 3.5)
     }
 
     @Test func repairsInvalidStoredValues() {
@@ -102,10 +105,12 @@ struct PreferencesTests {
         defaults.set(500.0, forKey: "fontSize")
         defaults.set("loud", forKey: "bell")
         defaults.set(-2.0, forKey: "opacity")
+        defaults.set(0.0, forKey: "scrollSpeed")
         let preferences = Preferences(defaults: defaults)
         #expect(preferences.fontSize == 13)
         #expect(preferences.bell == .visual)
         #expect(preferences.opacity == 0.9)
+        #expect(preferences.scrollSpeed == 2)
     }
 
     @Test func postsAChangeNotification() {

Tests/CodecUITests/PaneTests.swift

@@ -242,6 +242,35 @@ struct PaneTests {
         pane.changeFontSize(by: -100)
         #expect(pane.fontSize == 7)
     }
+
+    // MARK: Scrolling
+
+    @Test func aWheelNotchScrollsAsFarAsTheSettingSays() async throws {
+        let env = try TestEnvironment()
+        defer { env.tearDown() }
+        let pane = env.makePane()
+        defer { pane.shutDown() }
+        let window = makeTestWindow()
+        defer { window.close() }
+        window.contentView = pane.view
+        #expect(await waitUntil { pane.terminal.process.running })
+        pane.terminal.feed(text: (1...200).map { "line \($0)\r\n" }.joined())
+        func top() -> Int? { pane.terminal.terminalContentSnapshot(region: .viewport)?.rows.first?.absoluteRow }
+        func notchUp() throws {
+            let wheel = try #require(CGEvent(scrollWheelEvent2Source: nil, units: .line, wheelCount: 1, wheel1: 1, wheel2: 0, wheel3: 0))
+            pane.terminal.scrollWheel(with: try #require(NSEvent(cgEvent: wheel)))
+        }
+        let bottom = try #require(top())
+        #expect(bottom > 10)
+
+        // Twice the system's rate unless set otherwise.
+        try notchUp()
+        #expect(top() == bottom - 2)
+        env.preferences.scrollSpeed = 4
+        pane.applyPreferences()
+        try notchUp()
+        #expect(top() == bottom - 6)
+    }
 }
 
 @Suite("Pane context menu", .serialized, .timeLimit(.minutes(1)))

docs/command-line.md

@@ -27,7 +27,7 @@ Hold ⌘ to see what opens. Every file and folder name on screen is washed in th
 
 ![⌘ held over the output of ls: every name marked, one tagged with the file that opens](images/open-file.png)
 
-Copy on select is a setting (Settings › Shell › Selection). The scrollback keeps 10,000 lines; ⌘K clears it.
+Copy on select is a setting (Settings › Shell › Selection). The scrollback keeps 10,000 lines; ⌘K clears it. The trackpad and the mouse wheel scroll it twice as far as elsewhere on the Mac; Settings › Shell › Scrolling sets how far.
 
 ⌘F searches the scrollback. Every match on screen is tinted and the current one is outlined; the bar counts them ("3 of 14"), and marks down the pane's right edge show where the rest are. Return or ⌘G goes to the next match, ⇧Return or ⇧⌘G to the previous one (↓ and ↑ do too), wrapping around; Esc closes the bar. **Aa** matches case, **ab** whole words, **.\*** a regular expression. With text selected, ⌘F (or ⌘E) searches for it. Matches keep up as the pane prints more.
 

docs/settings.md

@@ -21,6 +21,7 @@ Open Settings with ⌘,. Changes apply as you make them, unless a setting says i
 - **Project environments**: whether to [activate a project's Python environment](prompt-and-status-bar.md#project-environments-zsh) (`.venv`) when you go into it, and your answer for each project: change it, forget it so Codec asks again, or remove the ones about projects that can't be found anymore, which are flagged.
 - **Apple Intelligence**: whether failed commands offer to be [explained](commands-sidebar.md#why-did-it-fail) by Apple's on-device model.
 - **History**: whether Codec records the commands you run, and a button to forget everything recorded so far. Forgetting also hides older commands from your shell's history file in Codec, without changing the file.
+- **Scrolling**: how far the trackpad and the mouse wheel scroll, from 1× (the scrollback follows your fingers, a line per notch of the wheel) to 5×. 2× by default.
 - **Selection**: copy text as soon as it's selected.
 
 ## Prompt