wezterm: add alternate_buffer_wheel_scroll_speed option and increase to 3

More details in the included docs.

closes: #432

config/src/lib.rs

@@ -861,6 +861,13 @@ pub struct Config {
 
     #[serde(default = "default_paste_source")]
     pub default_clipboard_paste_source: ClipboardPasteSource,
+
+    #[serde(default = "default_alternate_buffer_wheel_scroll_speed")]
+    pub alternate_buffer_wheel_scroll_speed: u8,
+}
+
+fn default_alternate_buffer_wheel_scroll_speed() -> u8 {
+    3
 }
 
 fn default_word_boundary() -> String {

config/src/terminal.rs

@@ -30,4 +30,8 @@ impl wezterm_term::TerminalConfiguration for TermConfig {
 
         config.resolved_palette.clone().into()
     }
+
+    fn alternate_buffer_wheel_scroll_speed(&self) -> u8 {
+        configuration().alternate_buffer_wheel_scroll_speed
+    }
 }

docs/changelog.markdown

@@ -53,6 +53,7 @@ brief notes about them may accumulate here.
 * New: Added a new default `CTRL-Insert` key assignment bound to `Copy`
 * macOS: Windows now have drop-shadows when they are opaque. These were disabled due transparency support was added. Thanks to [Rice](https://github.com/fanzeyi)! [#445](https://github.com/wez/wezterm/pull/445)
 * Unix: adjust font-config patterns to also match "dual spacing" fonts such as [Iosevka Term](https://typeof.net/Iosevka/). Thanks to [Leiser](https://github.com/leiserfg)! [#446](https://github.com/wez/wezterm/pull/446)
+* New: Added [alternate_buffer_wheel_scroll_speed](config/lua/config/alternate_buffer_wheel_scroll_speed.md) option to control how many cursor key presses are generated by the mouse wheel when the alternate screen is active. The new default for this is a faster-than-previous-releases 3 lines per wheel tick. [#432](https://github.com/wez/wezterm/issues/432)
 
 ### 20201101-103216-403d002d
 

docs/config/lua/config/alternate_buffer_wheel_scroll_speed.md

@@ -0,0 +1,25 @@
+# `alternate_buffer_wheel_scroll_speed = 3`
+
+*Since: nightly builds*
+
+Normally the vertical mouse wheel will scroll the terminal viewport
+so that different sections of the scrollback are visible.
+
+When an application activates the *Alternate Screen Buffer* (this is
+common for "full screen" terminal programs such as pagers and editors),
+the alternate screen doesn't have a scrollback.
+
+In this mode, if the application hasn't enabled mouse reporting, wezterm will
+generate Arrow Up/Down key events when the vertical mouse wheel is scrolled.
+
+The `alternate_buffer_wheel_scroll_speed` specifies how many arrow key presses
+are generated by a single scroll wheel "tick".
+
+The default for this value is `3`, which means that a single wheel up tick will
+appear to the application as though the user pressed arrow up three times in
+quick succession.
+
+In versions of wezterm prior to this configuration option being available, the
+behavior was the same except that the effective value of this option was always
+`1`.
+

term/src/config.rs

@@ -68,4 +68,8 @@ pub trait TerminalConfiguration: std::fmt::Debug {
     fn resize_preserves_scrollback(&self) -> bool {
         cfg!(windows)
     }
+
+    fn alternate_buffer_wheel_scroll_speed(&self) -> u8 {
+        3
+    }
 }

term/src/terminalstate.rs

@@ -531,14 +531,16 @@ impl TerminalState {
             self.writer.flush()?;
         } else if self.screen.is_alt_screen_active() {
             // Send cursor keys instead (equivalent to xterm's alternateScroll mode)
-            self.key_down(
-                match event.button {
-                    MouseButton::WheelDown(_) => KeyCode::DownArrow,
-                    MouseButton::WheelUp(_) => KeyCode::UpArrow,
-                    _ => bail!("unexpected mouse event"),
-                },
-                KeyModifiers::default(),
-            )?;
+            for _ in 0..self.config.alternate_buffer_wheel_scroll_speed() {
+                self.key_down(
+                    match event.button {
+                        MouseButton::WheelDown(_) => KeyCode::DownArrow,
+                        MouseButton::WheelUp(_) => KeyCode::UpArrow,
+                        _ => bail!("unexpected mouse event"),
+                    },
+                    KeyModifiers::default(),
+                )?;
+            }
         }
         Ok(())
     }