feat: configure half-page viewport scroll distance

src/editor.rs

@@ -13,7 +13,7 @@ use std::collections::{BTreeMap, HashMap, HashSet, VecDeque};
 use std::fmt;
 use std::fs::{self, OpenOptions};
 use std::io::{self, Read, Write};
-use std::num::NonZeroU8;
+use std::num::{NonZeroU8, NonZeroUsize};
 use std::ops::Range;
 #[cfg(unix)]
 use std::os::unix::fs::{MetadataExt, OpenOptionsExt};
@@ -2009,6 +2009,7 @@ pub struct Editor {
     popup: PopupConfig,
     labels: BTreeMap<String, String>,
     scroll_distance: Option<usize>,
+    scroll_half_page_lines: Option<NonZeroUsize>,
     highlight_trailing_whitespace: bool,
     whitespace_characters: BTreeMap<char, char>,
     whitespace_scope: WhitespaceScope,
@@ -2119,6 +2120,7 @@ impl Editor {
             popup: PopupConfig::default(),
             labels: BTreeMap::new(),
             scroll_distance: Some(0),
+            scroll_half_page_lines: None,
             highlight_trailing_whitespace: false,
             whitespace_characters: BTreeMap::new(),
             whitespace_scope: WhitespaceScope::All,
@@ -4116,6 +4118,10 @@ impl Editor {
         self.scroll_distance = distance;
     }
 
+    pub(crate) fn set_scroll_half_page_lines(&mut self, lines: Option<NonZeroUsize>) {
+        self.scroll_half_page_lines = lines;
+    }
+
     pub(crate) fn highlight_trailing_whitespace(&self) -> bool {
         self.highlight_trailing_whitespace
     }
@@ -5829,7 +5835,11 @@ impl Editor {
 
     pub(crate) fn take_viewport_scroll(&self, height: usize) -> isize {
         let (rows, halves) = self.active.view.viewport_scroll.take();
-        rows.saturating_add(halves.saturating_mul((height / 2).max(1) as isize))
+        let lines = self
+            .scroll_half_page_lines
+            .map_or((height / 2).max(1), NonZeroUsize::get);
+        let lines = isize::try_from(lines).unwrap_or(isize::MAX);
+        rows.saturating_add(halves.saturating_mul(lines))
     }
 
     fn reveal_caret(&mut self) {

src/main.rs

@@ -28,7 +28,7 @@ Normal: i/a insert, I/A insert at first nonblank/end, o/O new line
         _ splits above/below, | left/right; Option/Alt+h/j/k/l focuses neighboring panes
         Ctrl+Option/Alt+h/l previous/next tab; :tab.new opens current buffer in another tab
         Normal/Visual: prefix motions with counts (5j, 2w, 3n); Esc cancels count
-        Normal/Visual: Ctrl+u/d scroll half a viewport up/down without moving carets; counts supported
+        Normal/Visual: Ctrl+u/d scroll up/down without moving carets; configurable distance (default half viewport), counts supported
         u undo, U redo, : command, / search, * search word, n/N next/previous match
         yy copies whole lines; dd deletes them; cc changes them and enters Insert; counts: 3yy, 2dd, 2cc
         dw/db cut forward/backward words on the current line; cw/cb cut the same spans and enter Insert

src/ruby.rs

@@ -3,7 +3,7 @@ use crate::editor::{Context, Effect, Feature};
 use crate::plugin::{DocumentEvent, PluginEvent, PluginUpdate, UpdateEffect};
 use serde::{Deserialize, Serialize};
 use std::io::{self, BufRead, BufReader, Write};
-use std::num::NonZeroU8;
+use std::num::{NonZeroU8, NonZeroUsize};
 use std::path::{Path, PathBuf};
 use std::process::{Child, Command, Stdio};
 use std::sync::mpsc::{self, Receiver, RecvTimeoutError, SyncSender};
@@ -46,6 +46,7 @@ pub struct Config {
     pub popup: PopupConfig,
     pub labels: BTreeMap<String, String>,
     pub scroll_distance: Option<usize>,
+    pub scroll_half_page_lines: Option<NonZeroUsize>,
     pub highlight_trailing_whitespace: bool,
     pub whitespace_characters: BTreeMap<char, char>,
     pub whitespace_scope: crate::editor::WhitespaceScope,
@@ -97,6 +98,7 @@ impl Default for Config {
             popup: PopupConfig::default(),
             labels: BTreeMap::new(),
             scroll_distance: Some(0),
+            scroll_half_page_lines: None,
             highlight_trailing_whitespace: false,
             whitespace_characters: BTreeMap::new(),
             whitespace_scope: crate::editor::WhitespaceScope::All,
@@ -135,6 +137,7 @@ pub fn load_config(path: &Path) -> Result<Config, String> {
                 popup,
                 labels,
                 scroll_distance,
+                scroll_half_page_lines,
                 highlight_trailing_whitespace,
                 whitespace_characters,
                 whitespace_scope,
@@ -174,6 +177,7 @@ pub fn load_config(path: &Path) -> Result<Config, String> {
             config.popup = popup;
             config.labels = labels;
             config.scroll_distance = scroll_distance;
+            config.scroll_half_page_lines = scroll_half_page_lines;
             config.highlight_trailing_whitespace = highlight_trailing_whitespace;
             config.whitespace_characters = whitespace_characters;
             config.whitespace_scope = whitespace_scope;
@@ -512,6 +516,7 @@ struct ConfigFrame {
     labels: BTreeMap<String, String>,
     #[serde(deserialize_with = "scroll_distance")]
     scroll_distance: Option<usize>,
+    scroll_half_page_lines: Option<NonZeroUsize>,
     highlight_trailing_whitespace: bool,
     #[serde(deserialize_with = "whitespace_characters")]
     whitespace_characters: BTreeMap<char, char>,
@@ -1929,6 +1934,50 @@ end
         }
     }
 
+    #[test]
+    fn config_scroll_half_page_lines_controls_counted_scrolling_and_rejects_invalid_values() {
+        let fixture = Fixture::new();
+        for (value, expected) in [
+            ("nil", 30),
+            ("1", 3),
+            ("7", 21),
+            ("18446744073709551615", isize::MAX),
+        ] {
+            let path = fixture.file(
+                "config.rb",
+                &format!("Vamp.configure {{ |config| config.scroll_half_page_lines = {value} }}"),
+            );
+            let mut session =
+                crate::session::EditorSession::open(None, vec![], Some(&path)).unwrap();
+            session.handle(crate::editor::Input::Char('3'));
+            session.handle(crate::editor::Input::Ctrl('d'));
+            assert_eq!(
+                session.editor().take_viewport_scroll(20),
+                expected,
+                "{value}"
+            );
+        }
+        for value in [
+            "0",
+            "-1",
+            "1.5",
+            "\"3\"",
+            "true",
+            "false",
+            "18446744073709551616",
+        ] {
+            let path = fixture.file(
+                "config.rb",
+                &format!("Vamp.configure {{ |config| config.scroll_half_page_lines = {value} }}"),
+            );
+            let error = load_config(&path).unwrap_err();
+            assert!(
+                error.contains("scroll_half_page_lines") && error.contains("must be"),
+                "{value}: {error}"
+            );
+        }
+    }
+
     #[test]
     fn config_scroll_distance_accepts_nil_and_counts_and_rejects_invalid_values() {
         let fixture = Fixture::new();

src/ruby_config.rb

@@ -145,6 +145,7 @@ module Vamp
       @popup = PopupConfig.new
       @labels = {}
       @scroll_distance = 0
+      @scroll_half_page_lines = nil
       @highlight_trailing_whitespace = false
       @whitespace_characters = {}
       @whitespace_scope = "all"
@@ -229,6 +230,12 @@ module Vamp
       @scroll_distance = distance.nil? ? nil : diff_line_count!(distance, "scroll_distance", 0)
     end
 
+    # @param lines [Integer, nil] positive screen rows, or nil for half the viewport
+    # @return [Integer, nil]
+    def scroll_half_page_lines=(lines)
+      @scroll_half_page_lines = lines.nil? ? nil : diff_line_count!(lines, "scroll_half_page_lines", 1)
+    end
+
     # @param enabled [Boolean]
     # @return [Boolean]
     def highlight_trailing_whitespace=(enabled)
@@ -343,6 +350,7 @@ module Vamp
         "git_blame" => @git_blame,
         "git_gutter" => @git_gutter,
         "scroll_distance" => @scroll_distance,
+        "scroll_half_page_lines" => @scroll_half_page_lines,
         "highlight_trailing_whitespace" => @highlight_trailing_whitespace,
         "whitespace_characters" => @whitespace_characters,
         "whitespace_scope" => @whitespace_scope,

src/session.rs

@@ -512,6 +512,7 @@ impl EditorSession {
         editor.set_git_blame(config.git_blame);
         editor.set_gutter_style(config.git_gutter);
         editor.set_scroll_distance(config.scroll_distance);
+        editor.set_scroll_half_page_lines(config.scroll_half_page_lines);
         editor.set_highlight_trailing_whitespace(config.highlight_trailing_whitespace);
         editor.set_whitespace_characters(config.whitespace_characters);
         editor.set_whitespace_scope(config.whitespace_scope);

src/tui.rs

@@ -12617,6 +12617,19 @@ end
                     editor.handle(Input::Ctrl('u'));
                     render(&mut terminal, &mut views, &mut editor);
                     assert_eq!(offset(&views), initial);
+                    editor.set_scroll_half_page_lines(std::num::NonZeroUsize::new(3));
+                    editor.handle(Input::Char('2'));
+                    editor.handle(Input::Ctrl('d'));
+                    render(&mut terminal, &mut views, &mut editor);
+                    if !wrapped {
+                        assert_eq!(offset(&views), (initial.0 + 6, 0));
+                    }
+                    assert_eq!(editor.carets(), carets);
+                    assert_eq!(editor.selections(), selections);
+                    editor.handle(Input::Char('2'));
+                    editor.handle(Input::Ctrl('u'));
+                    render(&mut terminal, &mut views, &mut editor);
+                    assert_eq!(offset(&views), initial);
                     if !visual {
                         editor.handle(Input::Char('3'));
                         editor.handle(Input::Alt('j'));