Make normal scrolling line amount configurable

It is now possible to configure the amount of lines the viewport should
scroll when using the normal scrolling mode.

This fixes #1160.

4 files changed, 43 insertions, 10 deletions

diff --git a/alacritty.yml b/alacritty.yml
index fcc637c3..6e87ede3 100644
--- a/alacritty.yml
+++ b/alacritty.yml
@@ -219,6 +219,12 @@ mouse:
   # To disable this completely, set `faux_scrollback_lines` to 0.
   faux_scrollback_lines: 1
 
+  # Normal Scrolling
+  #
+  # Number of lines the viewport will move when scrolling in
+  # the terminal with scrollback enabled (>0).
+  normal_scrolling_lines: 300
+
 selection:
   semantic_escape_chars: ",│`|:\"' ()[]{}<>"
 
diff --git a/alacritty_macos.yml b/alacritty_macos.yml
index baf17e61..08287c87 100644
--- a/alacritty_macos.yml
+++ b/alacritty_macos.yml
@@ -200,6 +200,12 @@ mouse:
   # To disable this completely, set `faux_scrollback_lines` to 0.
   faux_scrollback_lines: 1
 
+  # Normal Scrolling
+  #
+  # Number of lines the viewport will move when scrolling in
+  # the terminal with scrollback enabled (>0).
+  normal_scrolling_lines: 3
+
 selection:
   semantic_escape_chars: ",│`|:\"' ()[]{}<>"
 
diff --git a/src/config.rs b/src/config.rs
index a6d67b4a..d0741d9e 100644
--- a/src/config.rs
+++ b/src/config.rs
@@ -85,17 +85,26 @@ pub struct Mouse {
     /// up/down arrows sent when scrolling in alt screen buffer
     #[serde(deserialize_with = "deserialize_faux_scrollback_lines")]
     #[serde(default="default_faux_scrollback_lines")]
-    pub faux_scrollback_lines: usize,
+    pub faux_scrollback_lines: u8,
+
+    /// Number of lines scrolled in normal buffer with scrollback
+    #[serde(deserialize_with = "deserialize_normal_scrolling_lines")]
+    #[serde(default="default_normal_scrolling_lines")]
+    pub normal_scrolling_lines: u8,
 }
 
-fn default_faux_scrollback_lines() -> usize {
+fn default_faux_scrollback_lines() -> u8 {
     1
 }
 
-fn deserialize_faux_scrollback_lines<'a, D>(deserializer: D) -> ::std::result::Result<usize, D::Error>
+fn default_normal_scrolling_lines() -> u8 {
+    3
+}
+
+fn deserialize_faux_scrollback_lines<'a, D>(deserializer: D) -> ::std::result::Result<u8, D::Error>
     where D: de::Deserializer<'a>
 {
-    match usize::deserialize(deserializer) {
+    match u8::deserialize(deserializer) {
         Ok(lines) => Ok(lines),
         Err(err) => {
             eprintln!("problem with config: {}; Using default value", err);
@@ -104,6 +113,18 @@ fn deserialize_faux_scrollback_lines<'a, D>(deserializer: D) -> ::std::result::R
     }
 }
 
+fn deserialize_normal_scrolling_lines<'a, D>(deserializer: D) -> ::std::result::Result<u8, D::Error>
+    where D: de::Deserializer<'a>
+{
+    match u8::deserialize(deserializer) {
+        Ok(lines) => Ok(lines),
+        Err(err) => {
+            eprintln!("problem with config: {}; Using default value", err);
+            Ok(default_normal_scrolling_lines())
+        },
+    }
+}
+
 impl Default for Mouse {
     fn default() -> Mouse {
         Mouse {
@@ -113,7 +134,8 @@ impl Default for Mouse {
             triple_click: ClickHandler {
                 threshold: Duration::from_millis(300),
             },
-            faux_scrollback_lines: 1,
+            faux_scrollback_lines: default_faux_scrollback_lines(),
+            normal_scrolling_lines: default_normal_scrolling_lines(),
         }
     }
 }
diff --git a/src/input.rs b/src/input.rs
index f7514d11..fabb3485 100644
--- a/src/input.rs
+++ b/src/input.rs
@@ -34,8 +34,6 @@ use term::SizeInfo;
 use term::mode::{self, TermMode};
 use util::fmt::Red;
 
-const SCROLL_MULTIPLIER: usize = 3;
-
 /// Processes input from glutin.
 ///
 /// An escape sequence may be emitted in case specific keys or key combinations
@@ -399,8 +397,9 @@ impl<'a, A: ActionContext + 'a> Processor<'a, A> {
                     65
                 };
 
+                let scrolling_multiplier = self.mouse_config.normal_scrolling_lines;
                 for _ in 0..(to_scroll.abs() as usize) {
-                    self.scroll_terminal(mouse_modes, code, modifiers, SCROLL_MULTIPLIER)
+                    self.scroll_terminal(mouse_modes, code, modifiers, scrolling_multiplier)
                 }
 
                 self.ctx.mouse_mut().lines_scrolled = to_scroll % 1.0;
@@ -433,10 +432,10 @@ impl<'a, A: ActionContext + 'a> Processor<'a, A> {
         }
     }
 
-    fn scroll_terminal(&mut self, mouse_modes: TermMode, code: u8, modifiers: ModifiersState, scroll_multiplier: usize) {
+    fn scroll_terminal(&mut self, mouse_modes: TermMode, code: u8, modifiers: ModifiersState, scroll_multiplier: u8) {
         debug_assert!(code == 64 || code == 65);
 
-        let faux_scrollback_lines = self.mouse_config.faux_scrollback_lines;
+        let faux_scrollback_lines = self.mouse_config.faux_scrollback_lines as usize;
         if self.ctx.terminal_mode().intersects(mouse_modes) {
             self.mouse_report(code, ElementState::Pressed);
         } else if self.ctx.terminal_mode().contains(TermMode::ALT_SCREEN)