Feature: half page scrolling (#774)

* add ctrl-u/ctrl-d to process table

* add help text for ctrl-u/ctrl-d

* add ctrl-u/ctrl-d to help dialog

* store height of help menu, fix overscroll with half page down on help menu

Co-authored-by: ClementTsang <34804052+ClementTsang@users.noreply.github.com>

5 files changed, 62 insertions, 10 deletions

diff --git a/src/app.rs b/src/app.rs
index c1a5c969..b0965c1c 100644
--- a/src/app.rs
+++ b/src/app.rs
@@ -996,6 +996,49 @@ impl App {
         }
     }
 
+    pub fn scroll_half_page_up(&mut self) {
+        if self.help_dialog_state.is_showing_help {
+            let current = &mut self.help_dialog_state.scroll_state.current_scroll_index;
+            let amount = self.help_dialog_state.height / 2;
+
+            *current = current.saturating_sub(amount);
+        } else if self.current_widget.widget_type.is_widget_table() {
+            if let (Some((_tlc_x, tlc_y)), Some((_brc_x, brc_y))) = (
+                &self.current_widget.top_left_corner,
+                &self.current_widget.bottom_right_corner,
+            ) {
+                let border_offset = if self.is_drawing_border() { 1 } else { 0 };
+                let header_offset = self.header_offset(&self.current_widget);
+                let height = brc_y - tlc_y - 2 * border_offset - header_offset;
+                self.change_position_count(-(height as i64) / 2);
+            }
+        }
+    }
+
+    pub fn scroll_half_page_down(&mut self) {
+        if self.help_dialog_state.is_showing_help {
+            let current = &mut self.help_dialog_state.scroll_state.current_scroll_index;
+            let amount = self.help_dialog_state.height / 2;
+
+            *current = (*current + amount).min(
+                self.help_dialog_state
+                    .scroll_state
+                    .max_scroll_index
+                    .saturating_sub(1),
+            );
+        } else if self.current_widget.widget_type.is_widget_table() {
+            if let (Some((_tlc_x, tlc_y)), Some((_brc_x, brc_y))) = (
+                &self.current_widget.top_left_corner,
+                &self.current_widget.bottom_right_corner,
+            ) {
+                let border_offset = if self.is_drawing_border() { 1 } else { 0 };
+                let header_offset = self.header_offset(&self.current_widget);
+                let height = brc_y - tlc_y - 2 * border_offset - header_offset;
+                self.change_position_count(height as i64 / 2);
+            }
+        }
+    }
+
     pub fn skip_cursor_beginning(&mut self) {
         if !self.ignore_normal_keybinds() {
             if let BottomWidgetType::ProcSearch = self.current_widget.widget_type {
diff --git a/src/app/states.rs b/src/app/states.rs
index 4687d822..2ca18c0b 100644
--- a/src/app/states.rs
+++ b/src/app/states.rs
@@ -67,6 +67,7 @@ pub struct AppDeleteDialogState {
 
 pub struct AppHelpDialogState {
     pub is_showing_help: bool,
+    pub height: u16,
     pub scroll_state: ParagraphScrollState,
     pub index_shortcuts: Vec<u16>,
 }
@@ -75,6 +76,7 @@ impl Default for AppHelpDialogState {
     fn default() -> Self {
         AppHelpDialogState {
             is_showing_help: false,
+            height: 0,
             scroll_state: ParagraphScrollState::default(),
             index_shortcuts: vec![0; constants::HELP_TEXT.len()],
         }
diff --git a/src/canvas/dialogs/help_dialog.rs b/src/canvas/dialogs/help_dialog.rs
index 494da366..df76d52d 100644
--- a/src/canvas/dialogs/help_dialog.rs
+++ b/src/canvas/dialogs/help_dialog.rs
@@ -1,3 +1,5 @@
+use std::cmp::max;
+
 use unicode_width::UnicodeWidthStr;
 
 use crate::{app::App, canvas::Painter, constants};
@@ -30,12 +32,20 @@ impl Painter {
             ),
         ]);
 
+        let block = Block::default()
+            .title(help_title)
+            .style(self.colours.border_style)
+            .borders(Borders::ALL)
+            .border_style(self.colours.border_style);
+
         if app_state.should_get_widget_bounds() {
+            app_state.help_dialog_state.height = block.inner(draw_loc).height;
+
             // We must also recalculate how many lines are wrapping to properly get scrolling to work on
             // small terminal sizes... oh joy.
 
             let mut overflow_buffer = 0;
-            let paragraph_width = std::cmp::max(draw_loc.width.saturating_sub(2), 1);
+            let paragraph_width = max(draw_loc.width.saturating_sub(2), 1);
             let mut prev_section_len = 0;
 
             constants::HELP_TEXT
@@ -92,13 +102,7 @@ impl Painter {
 
         f.render_widget(
             Paragraph::new(self.styled_help_text.clone())
-                .block(
-                    Block::default()
-                        .title(help_title)
-                        .style(self.colours.border_style)
-                        .borders(Borders::ALL)
-                        .border_style(self.colours.border_style),
-                )
+                .block(block)
                 .style(self.colours.text_style)
                 .alignment(Alignment::Left)
                 .wrap(Wrap { trim: true })
diff --git a/src/constants.rs b/src/constants.rs
index 9ac719b3..f77c1864 100644
--- a/src/constants.rs
+++ b/src/constants.rs
@@ -226,7 +226,7 @@ pub const HELP_CONTENTS_TEXT: [&str; 8] = [
 
 // TODO [Help]: Search in help?
 // TODO [Help]: Move to using tables for easier formatting?
-pub const GENERAL_HELP_TEXT: [&str; 31] = [
+pub const GENERAL_HELP_TEXT: [&str; 32] = [
     "1 - General",
     "q, Ctrl-c        Quit",
     "Esc              Close dialog windows, search, widgets, or exit expanded mode",
@@ -256,6 +256,7 @@ pub const GENERAL_HELP_TEXT: [&str; 31] = [
     "-                Zoom out on chart (increase time range)",
     "=                Reset zoom",
     "PgUp, PgDown     Scroll up/down a table by a page",
+    "Ctrl-u, Ctrl-d   Scroll up/down a table by half a page",
     "Mouse scroll     Scroll through the tables or zoom in/out of charts by scrolling up/down",
     "Mouse click      Selects the clicked widget, table entry, dialog option, or tab",
 ];
diff --git a/src/lib.rs b/src/lib.rs
index c7bdfb6c..4c5c099b 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -166,9 +166,11 @@ pub fn handle_key_event_or_break(
                 }
                 KeyCode::Char('a') => app.skip_cursor_beginning(),
                 KeyCode::Char('e') => app.skip_cursor_end(),
-                KeyCode::Char('u') => app.clear_search(),
+                KeyCode::Char('u') if app.is_in_search_widget() => app.clear_search(),
                 KeyCode::Char('w') => app.clear_previous_word(),
                 KeyCode::Char('h') => app.on_backspace(),
+                KeyCode::Char('d') => app.scroll_half_page_down(),
+                KeyCode::Char('u') => app.scroll_half_page_up(),
                 // KeyCode::Char('j') => {}, // Move down
                 // KeyCode::Char('k') => {}, // Move up
                 // KeyCode::Char('h') => {}, // Move right