Process shift+pageup/down at the gui layer

Refs: https://github.com/wez/wezterm/issues/106

docs/config/keys.markdown

@@ -46,6 +46,8 @@ The default key bindings are:
 | `SUPER+SHIFT` | `]` | `ActivateTabRelative(1)` |
 | `CTRL+SHIFT`     | `PAGEUP`      | `MoveTabRelative(-1)` |
 | `CTRL+SHIFT`     | `PAGEDOWN`      | `MoveTabRelative(1)` |
+| `SHIFT`          | `PAGEUP`      | `ScrollByPage(-1)` |
+| `SHIFT`          | `PAGEDOWN`    | `ScrollByPage(1)` |
 
 These can be overridden using the `keys` section in your `~/.wezterm.toml` config file.
 For example, you can disable a default assignment like this:
@@ -113,6 +115,7 @@ specified via the `arg` key; see examples below.
 | `CloseCurrentTab` | Equivalent to clicking the `x` on the window title bar to close it: Closes the current tab.  If that was the last tab, closes that window.  If that was the last window, wezterm terminates. |
 | `MoveTabRelative` | Move the current tab relative to its peers.  The `arg` value specifies an offset. eg: `-1` moves the tab to the left of the current tab, while `1` moves the tab to the right. |
 | `MoveTab` | Move the tab so that it has the index specified by the `arg` value. eg: `0` moves the tab to be  leftmost, while `1` moves the tab so that it is second tab from the left, and so on. |
+| `ScrollByPage` | Adjusts the scroll position by the number of pages specified by the `arg` value. Negative values scroll upwards, while positive values scroll downwards. |
 
 Example:
 

src/config/keys.rs

@@ -76,6 +76,12 @@ impl std::convert::TryInto<KeyAssignment> for &Key {
                     .ok_or_else(|| anyhow!("missing arg for {:?}", self))?
                     .parse()?,
             ),
+            KeyAction::ScrollByPage => KeyAssignment::ScrollByPage(
+                self.arg
+                    .as_ref()
+                    .ok_or_else(|| anyhow!("missing arg for {:?}", self))?
+                    .parse()?,
+            ),
         })
     }
 }
@@ -102,6 +108,7 @@ pub enum KeyAction {
     ReloadConfiguration,
     MoveTab,
     MoveTabRelative,
+    ScrollByPage,
 }
 
 fn de_keycode<'de, D>(deserializer: D) -> Result<KeyCode, D::Error>

src/frontend/gui/termwindow.rs

@@ -1087,6 +1087,26 @@ impl TermWindow {
         Ok(())
     }
 
+    fn scroll_by_page(&mut self, amount: isize) -> anyhow::Result<()> {
+        let mux = Mux::get().unwrap();
+        let tab = match mux.get_active_tab_for_window(self.mux_window_id) {
+            Some(tab) => tab,
+            None => return Ok(()),
+        };
+        let mut render = tab.renderer();
+        let dims = render.get_dimensions();
+        let position = self
+            .get_viewport(tab.tab_id())
+            .unwrap_or(dims.physical_top)
+            .saturating_add(amount * dims.viewport_rows as isize);
+        self.set_viewport(tab.tab_id(), Some(position), dims);
+        render.make_all_lines_dirty();
+        if let Some(win) = self.window.as_ref() {
+            win.invalidate();
+        }
+        Ok(())
+    }
+
     fn move_tab_relative(&mut self, delta: isize) -> anyhow::Result<()> {
         let mux = Mux::get().unwrap();
         let window = mux
@@ -1211,6 +1231,7 @@ impl TermWindow {
             ReloadConfiguration => crate::config::reload(),
             MoveTab(n) => self.move_tab(*n)?,
             MoveTabRelative(n) => self.move_tab_relative(*n)?,
+            ScrollByPage(n) => self.scroll_by_page(*n)?,
         };
         Ok(())
     }

src/keyassignment.rs

@@ -37,6 +37,7 @@ pub enum KeyAssignment {
     ReloadConfiguration,
     MoveTabRelative(isize),
     MoveTab(usize),
+    ScrollByPage(isize),
 }
 
 pub struct KeyMap(HashMap<(KeyCode, KeyModifiers), KeyAssignment>);
@@ -143,6 +144,8 @@ impl KeyMap {
             [ctrl_shift, KeyCode::Char('R'), ReloadConfiguration],
             [ctrl_shift, KeyCode::PageUp, MoveTabRelative(-1)],
             [ctrl_shift, KeyCode::PageDown, MoveTabRelative(1)],
+            [KeyModifiers::SHIFT, KeyCode::PageUp, ScrollByPage(-1)],
+            [KeyModifiers::SHIFT, KeyCode::PageDown, ScrollByPage(1)],
         );
 
         Self(map)