Allow faux scroll amount configuration

It is now possible to configure the amount of lines
scrolled with faux scrollback.

alacritty.yml

@@ -197,9 +197,21 @@ background_opacity: 1.0
 mouse_bindings:
   - { mouse: Middle, action: PasteSelection }
 
+# Mouse settings
+#
+# The `faux_scrollback_lines` setting controls the number
+# of lines the terminal should scroll when the alternate
+# screen buffer is active. This is used to allow mouse
+# scrolling for applications like `man`.
+# To disable this completely, set `faux_scrollback_lines` to 0.
+#
+# The `double_click` and `triple_click` settings control the time
+# alacritty should wait for accepting multiple clicks as one double
+# or triple click.
 mouse:
   double_click: { threshold: 300 }
   triple_click: { threshold: 300 }
+  faux_scrollback_lines: 1
 
 selection:
   semantic_escape_chars: ",│`|:\"' ()[]{}<>"

alacritty_macos.yml

@@ -178,9 +178,21 @@ background_opacity: 1.0
 mouse_bindings:
   - { mouse: Middle, action: PasteSelection }
 
+# Mouse settings
+#
+# The `faux_scrollback_lines` setting controls the number
+# of lines the terminal should scroll when the alternate
+# screen buffer is active. This is used to allow mouse
+# scrolling for applications like `man`.
+# To disable this completely, set `faux_scrollback_lines` to 0.
+#
+# The `double_click` and `triple_click` settings control the time
+# alacritty should wait for accepting multiple clicks as one double
+# or triple click.
 mouse:
   double_click: { threshold: 300 }
   triple_click: { threshold: 300 }
+  faux_scrollback_lines: 1
 
 selection:
   semantic_escape_chars: ",│`|:\"' ()[]{}<>"

src/config.rs

@@ -66,9 +66,13 @@ pub struct Mouse {
     pub double_click: ClickHandler,
     pub triple_click: ClickHandler,
 
-    /// Send up/down arrow when scrolling in alt screen buffer
+    /// up/down arrows sent when scrolling in alt screen buffer
-    #[serde(default="true_bool")]
+    #[serde(default="default_faux_scrollback_lines")]
-    pub faux_scrollback: bool,
+    pub faux_scrollback_lines: usize,
+}
+
+fn default_faux_scrollback_lines() -> usize {
+    1
 }
 
 impl Default for Mouse {
@@ -80,7 +84,7 @@ impl Default for Mouse {
             triple_click: ClickHandler {
                 threshold: Duration::from_millis(300),
             },
-            faux_scrollback: true,
+            faux_scrollback_lines: 1,
         }
     }
 }

src/input.rs

@@ -375,9 +375,8 @@ impl<'a, A: ActionContext + 'a> Processor<'a, A> {
     }
 
     pub fn on_mouse_wheel(&mut self, delta: MouseScrollDelta, phase: TouchPhase) {
-        let modes = mode::TermMode::MOUSE_REPORT_CLICK | mode::TermMode::MOUSE_MOTION | mode::TermMode::SGR_MOUSE |
+        let mouse_modes = mode::TermMode::MOUSE_REPORT_CLICK | mode::TermMode::MOUSE_MOTION | mode::TermMode::SGR_MOUSE;
-            mode::TermMode::ALT_SCREEN;
+        if !self.ctx.terminal_mode().intersects(mouse_modes | mode::TermMode::ALT_SCREEN) {
-        if !self.ctx.terminal_mode().intersects(modes) {
             return;
         }
 
@@ -391,20 +390,7 @@ impl<'a, A: ActionContext + 'a> Processor<'a, A> {
                 };
 
                 for _ in 0..(to_scroll.abs() as usize) {
-                    if self.mouse_config.faux_scrollback &&
+                    self.scroll_terminal(mouse_modes, code)
-                        self.ctx.terminal_mode().intersects(mode::TermMode::ALT_SCREEN)
-                    {
-                        // Faux scrolling
-                        if code == 64 {
-                            // Scroll up one line
-                            self.ctx.write_to_pty("\x1bOA".as_bytes());
-                        } else {
-                            // Scroll down one line
-                            self.ctx.write_to_pty("\x1bOB".as_bytes());
-                        }
-                    } else {
-                        self.normal_mouse_report(code);
-                    }
                 }
 
                 self.ctx.mouse_mut().lines_scrolled = to_scroll % 1.0;
@@ -420,7 +406,7 @@ impl<'a, A: ActionContext + 'a> Processor<'a, A> {
                         let height = self.ctx.size_info().cell_height as i32;
 
                         while self.ctx.mouse_mut().scroll_px.abs() >= height {
-                            let button = if self.ctx.mouse_mut().scroll_px > 0 {
+                            let code = if self.ctx.mouse_mut().scroll_px > 0 {
                                 self.ctx.mouse_mut().scroll_px -= height;
                                 64
                             } else {
@@ -428,20 +414,7 @@ impl<'a, A: ActionContext + 'a> Processor<'a, A> {
                                 65
                             };
 
-                            if self.mouse_config.faux_scrollback &&
+                            self.scroll_terminal(mouse_modes, code)
-                                self.ctx.terminal_mode().intersects(mode::TermMode::ALT_SCREEN)
-                            {
-                                // Faux scrolling
-                                if button == 64 {
-                                    // Scroll up one line
-                                    self.ctx.write_to_pty("\x1bOA".as_bytes());
-                                } else {
-                                    // Scroll down one line
-                                    self.ctx.write_to_pty("\x1bOB".as_bytes());
-                                }
-                            } else {
-                                self.normal_mouse_report(button);
-                            }
                         }
                     },
                     _ => (),
@@ -450,6 +423,30 @@ impl<'a, A: ActionContext + 'a> Processor<'a, A> {
         }
     }
 
+    fn scroll_terminal(&mut self, mouse_modes: TermMode, code: u8) {
+        let faux_scrollback_lines = self.mouse_config.faux_scrollback_lines;
+        if self.ctx.terminal_mode().intersects(mouse_modes) {
+            self.normal_mouse_report(code);
+        } else if faux_scrollback_lines > 0 {
+            // Faux scrolling
+            if code == 64 {
+                // Scroll up by `faux_scrollback_lines`
+                let mut content = String::with_capacity(faux_scrollback_lines * 3);
+                for _ in 0..faux_scrollback_lines {
+                    content = content + "\x1bOA";
+                }
+                self.ctx.write_to_pty(content.into_bytes());
+            } else {
+                // Scroll down by `faux_scrollback_lines`
+                let mut content = String::with_capacity(faux_scrollback_lines * 3);
+                for _ in 0..faux_scrollback_lines {
+                    content = content + "\x1bOB";
+                }
+                self.ctx.write_to_pty(content.into_bytes());
+            }
+        }
+    }
+
     pub fn on_focus_change(&mut self, is_focused: bool) {
         if self.ctx.terminal_mode().contains(mode::TermMode::FOCUS_IN_OUT) {
             let chr = if is_focused {
@@ -702,7 +699,8 @@ mod tests {
                         },
                         triple_click: ClickHandler {
                             threshold: Duration::from_millis(1000),
-                        }
+                        },
+                        faux_scrollback_lines: 1,
                     },
                     key_bindings: &config.key_bindings()[..],
                     mouse_bindings: &config.mouse_bindings()[..],