feat(scrolling): half-page scroll actions (#813)

* Half-page scroll actions #794

* fix(performance): do not hang when resizing large line wraps (#814)

* fix(performance): do not hang when resizing large line wraps

* style(fmt): make rustfmt happy

* style(clippy): make clippy happy

* docs(changelog): scroll fix

* fix(compatibility): home and end key fix (#815)

* fix(compatibility): handle home/end keys properly from terminfo

* style(fmt): make rustfmt happy

* style(fmt): remove unused import

* docs(changelog): home end key fix

* docs(changelog): fix link

* fix(typo): Correct typo from `occured` to `occurred` (#821)

* docs(changelog): fix a typo

* fix(docs): fix wrong arguments for `cargo make run` given in CONTRIBUTING.md (#819)

* docs(changelog): update `cargo-make` for `v0.35.3`

* fix(warning): Fix an unused import warning of std::fs on macos (#820)

* docs(changelog): fix unused import on darwin

* add: `WriteChars` action (#825)

* Behaves like the `Write` action, but one can specify
  strings themselves instead of their bytecodes.

  Usage:

  WriteChars: "cargo make test",

* docs(changelog): Add `WriteChars` action

* fix(docs): Fix a typo and some grammatical errors in bug_report.md (#826)

* docs(changelog): fix typo bug_report template

* add: `rust-version` (msrv) field to `Cargo.toml` (#828)

* specifies the minimum version the package can be compiled with,
  may be ignored with `--ignore-rust-version` option

  ref: https://doc.rust-lang.org/nightly/cargo/reference/manifest.html#the-rust-version-field

* docs(changelog): add `rust-version` to `Cargo.toml`

* fix(unix): forkpty => openpty (#830)

* fix(unix): forkpty => openpty

* style(fmt): make rustfmt happy

* docs(changelog): forkpty => openpty

* Fix: move `colors_transform` to `colorsys` (#832)

* `colors_transform` is deprecated and superceded by `colorsys`

  ref: https://crates.io/crates/colors-transform

* docs(changelog): `colors_transform` to `colorsys`

* feat(ui): add right-click support to plugins

* chore(docs): update changelog

* chore(warnings): remove unused imports (#833)

* rename var sroll_rows and review snapshots

* style(fmt): make rustfmt happy

Co-authored-by: Aram Drevekenin <aram@poor.dev>
Co-authored-by: Ken Matsui <26405363+ken-matsui@users.noreply.github.com>
Co-authored-by: a-kenji <aks.kenji@protonmail.com>
Co-authored-by: Tw <tw19881113@gmail.com>
Co-authored-by: Brooks Rady <b.j.rady@gmail.com>

8 files changed, 73 insertions, 5 deletions

diff --git a/src/tests/e2e/snapshots/zellij__tests__e2e__cases__scrolling_inside_a_pane.snap b/src/tests/e2e/snapshots/zellij__tests__e2e__cases__scrolling_inside_a_pane.snap
index fdea92b7a..664e881b4 100644
--- a/src/tests/e2e/snapshots/zellij__tests__e2e__cases__scrolling_inside_a_pane.snap
+++ b/src/tests/e2e/snapshots/zellij__tests__e2e__cases__scrolling_inside_a_pane.snap
@@ -26,4 +26,4 @@ expression: last_snapshot
 │                                                          ││line19 00000000000000000000000000000000000000000000000000█│
 └──────────────────────────────────────────────────────────┘└──────────────────────────────────────────────────────────┘
  Ctrl + <g> LOCK  <p> PANE  <t> TAB  <n> RESIZE  <h> MOVE  <s> SCROLL  <o> SESSION  <q> QUIT           
- <↓↑> Scroll / <PgUp/PgDn> Scroll Page / <ENTER> Select pane                                                            
+ <↓↑> Scroll / <PgUp/PgDn> Scroll Page / <u/d> Scroll Half Page / <ENTER> Select pane                                   
diff --git a/zellij-server/src/route.rs b/zellij-server/src/route.rs
index 444be5a08..457354916 100644
--- a/zellij-server/src/route.rs
+++ b/zellij-server/src/route.rs
@@ -183,6 +183,18 @@ fn route_action(
                 .send_to_screen(ScreenInstruction::PageScrollDown(client_id))
                 .unwrap();
         }
+        Action::HalfPageScrollUp => {
+            session
+                .senders
+                .send_to_screen(ScreenInstruction::HalfPageScrollUp(client_id))
+                .unwrap();
+        }
+        Action::HalfPageScrollDown => {
+            session
+                .senders
+                .send_to_screen(ScreenInstruction::HalfPageScrollDown(client_id))
+                .unwrap();
+        }
         Action::ToggleFocusFullscreen => {
             session
                 .senders
diff --git a/zellij-server/src/screen.rs b/zellij-server/src/screen.rs
index 2a8c54c6a..fb225f78a 100644
--- a/zellij-server/src/screen.rs
+++ b/zellij-server/src/screen.rs
@@ -59,6 +59,8 @@ pub(crate) enum ScreenInstruction {
     ScrollToBottom(ClientId),
     PageScrollUp(ClientId),
     PageScrollDown(ClientId),
+    HalfPageScrollUp(ClientId),
+    HalfPageScrollDown(ClientId),
     ClearScroll(ClientId),
     CloseFocusedPane(ClientId),
     ToggleActiveTerminalFullscreen(ClientId),
@@ -123,6 +125,8 @@ impl From<&ScreenInstruction> for ScreenContext {
             ScreenInstruction::ScrollToBottom(..) => ScreenContext::ScrollToBottom,
             ScreenInstruction::PageScrollUp(..) => ScreenContext::PageScrollUp,
             ScreenInstruction::PageScrollDown(..) => ScreenContext::PageScrollDown,
+            ScreenInstruction::HalfPageScrollUp(..) => ScreenContext::HalfPageScrollUp,
+            ScreenInstruction::HalfPageScrollDown(..) => ScreenContext::HalfPageScrollDown,
             ScreenInstruction::ClearScroll(..) => ScreenContext::ClearScroll,
             ScreenInstruction::CloseFocusedPane(..) => ScreenContext::CloseFocusedPane,
             ScreenInstruction::ToggleActiveTerminalFullscreen(..) => {
@@ -848,6 +852,22 @@ pub(crate) fn screen_thread_main(
 
                 screen.render();
             }
+            ScreenInstruction::HalfPageScrollUp(client_id) => {
+                screen
+                    .get_active_tab_mut(client_id)
+                    .unwrap()
+                    .scroll_active_terminal_up_half_page();
+
+                screen.render();
+            }
+            ScreenInstruction::HalfPageScrollDown(client_id) => {
+                screen
+                    .get_active_tab_mut(client_id)
+                    .unwrap()
+                    .scroll_active_terminal_down_half_page();
+
+                screen.render();
+            }
             ScreenInstruction::ClearScroll(client_id) => {
                 screen
                     .get_active_tab_mut(client_id)
diff --git a/zellij-server/src/tab.rs b/zellij-server/src/tab.rs
index ffdf7e647..083984178 100644
--- a/zellij-server/src/tab.rs
+++ b/zellij-server/src/tab.rs
@@ -2899,8 +2899,8 @@ impl Tab {
                 .get_mut(&PaneId::Terminal(active_terminal_id))
                 .unwrap();
             // prevent overflow when row == 0
-            let scroll_columns = active_terminal.rows().max(1) - 1;
-            active_terminal.scroll_up(scroll_columns);
+            let scroll_rows = active_terminal.rows().max(1) - 1;
+            active_terminal.scroll_up(scroll_rows);
         }
     }
     pub fn scroll_active_terminal_down_page(&mut self) {
@@ -2910,8 +2910,33 @@ impl Tab {
                 .get_mut(&PaneId::Terminal(active_terminal_id))
                 .unwrap();
             // prevent overflow when row == 0
-            let scroll_columns = active_terminal.rows().max(1) - 1;
-            active_terminal.scroll_down(scroll_columns);
+            let scroll_rows = active_terminal.rows().max(1) - 1;
+            active_terminal.scroll_down(scroll_rows);
+            if !active_terminal.is_scrolled() {
+                self.process_pending_vte_events(active_terminal_id);
+            }
+        }
+    }
+    pub fn scroll_active_terminal_up_half_page(&mut self) {
+        if let Some(active_terminal_id) = self.get_active_terminal_id() {
+            let active_terminal = self
+                .panes
+                .get_mut(&PaneId::Terminal(active_terminal_id))
+                .unwrap();
+            // prevent overflow when row == 0
+            let scroll_rows = (active_terminal.rows().max(1) - 1) / 2;
+            active_terminal.scroll_up(scroll_rows);
+        }
+    }
+    pub fn scroll_active_terminal_down_half_page(&mut self) {
+        if let Some(active_terminal_id) = self.get_active_terminal_id() {
+            let active_terminal = self
+                .panes
+                .get_mut(&PaneId::Terminal(active_terminal_id))
+                .unwrap();
+            // prevent overflow when row == 0
+            let scroll_rows = (active_terminal.rows().max(1) - 1) / 2;
+            active_terminal.scroll_down(scroll_rows);
             if !active_terminal.is_scrolled() {
                 self.process_pending_vte_events(active_terminal_id);
             }
diff --git a/zellij-utils/assets/config/default.yaml b/zellij-utils/assets/config/default.yaml
index b1a1ad2e3..35dc2311d 100644
--- a/zellij-utils/assets/config/default.yaml
+++ b/zellij-utils/assets/config/default.yaml
@@ -265,6 +265,10 @@ keybinds:
           key: [Ctrl: 'f', PageDown, Right, Char: 'l',]
         - action: [PageScrollUp,]
           key: [Ctrl: 'b', PageUp, Left, Char: 'h',]
+        - action: [HalfPageScrollDown,]
+          key: [Char: 'd',]
+        - action: [HalfPageScrollUp,]
+          key: [Char: 'u',]
         - action: [NewPane: ,]
           key: [ Alt: 'n',]
         - action: [MoveFocus: Left,]
diff --git a/zellij-utils/src/errors.rs b/zellij-utils/src/errors.rs
index 6dae0d1ac..7088c30ce 100644
--- a/zellij-utils/src/errors.rs
+++ b/zellij-utils/src/errors.rs
@@ -239,6 +239,8 @@ pub enum ScreenContext {
     ScrollToBottom,
     PageScrollUp,
     PageScrollDown,
+    HalfPageScrollUp,
+    HalfPageScrollDown,
     ClearScroll,
     CloseFocusedPane,
     ToggleActiveSyncTab,
diff --git a/zellij-utils/src/input/actions.rs b/zellij-utils/src/input/actions.rs
index 13d3566de..bd43206cf 100644
--- a/zellij-utils/src/input/actions.rs
+++ b/zellij-utils/src/input/actions.rs
@@ -68,6 +68,10 @@ pub enum Action {
     PageScrollUp,
     /// Scroll down one page in focus pane.
     PageScrollDown,
+    /// Scroll up half page in focus pane.
+    HalfPageScrollUp,
+    /// Scroll down half page in focus pane.
+    HalfPageScrollDown,
     /// Toggle between fullscreen focus pane and normal layout.
     ToggleFocusFullscreen,
     /// Toggle frames around panes in the UI
diff --git a/zellij-utils/src/input/mod.rs b/zellij-utils/src/input/mod.rs
index c0a0f1aee..613b8d172 100644
--- a/zellij-utils/src/input/mod.rs
+++ b/zellij-utils/src/input/mod.rs
@@ -51,6 +51,7 @@ pub fn get_mode_info(
         InputMode::Scroll => vec![
             ("↓↑".to_string(), "Scroll".to_string()),
             ("PgUp/PgDn".to_string(), "Scroll Page".to_string()),
+            ("u/d".to_string(), "Scroll Half Page".to_string()),
         ],
         InputMode::RenameTab => vec![("Enter".to_string(), "when done".to_string())],
         InputMode::Session => vec![("d".to_string(), "Detach".to_string())],