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) {