Unify the grid line indexing types

Previously Alacritty was using two different ways to reference lines in
the terminal. Either a `usize`, or a `Line(usize)`. These indexing
systems both served different purposes, but made it difficult to reason
about logic involving these systems because of its inconsistency.

To resolve this issue, a single new `Line(i32)` type has been
introduced.  All existing references to lines and points now rely on
this definition of a line.

The indexing starts at the top of the terminal region with the line 0,
which matches the line 1 used by escape sequences. Each line in the
history becomes increasingly negative and the bottommost line is equal
to the number of visible lines minus one.

Having a system which goes into the negatives allows following the
escape sequence's indexing system closely, while at the same time making
it trivial to implement `Ord` for points.

The Alacritty UI crate is the only place which has a different indexing
system, since rendering and input puts the zero line at the top of the
viewport, rather than the top of the terminal region.

All instances which refer to a number of lines/columns instead of just a
single Line/Column have also been changed to use a `usize` instead. This
way a Line/Column will always refer to a specific place in the grid and
no confusion is created by having a count of lines as a possible index
into the grid storage.

1 files changed, 3 insertions, 3 deletions

diff --git a/alacritty/src/config/window.rs b/alacritty/src/config/window.rs
index 2d501b91..d74390d8 100644
--- a/alacritty/src/config/window.rs
+++ b/alacritty/src/config/window.rs
@@ -8,7 +8,7 @@ use serde::{Deserialize, Deserializer};
 
 use alacritty_config_derive::ConfigDeserialize;
 use alacritty_terminal::config::LOG_TARGET_CONFIG;
-use alacritty_terminal::index::{Column, Line};
+use alacritty_terminal::index::Column;
 
 use crate::config::ui_config::Delta;
 
@@ -74,7 +74,7 @@ impl WindowConfig {
     #[inline]
     pub fn dimensions(&self) -> Option<Dimensions> {
         if self.dimensions.columns.0 != 0
-            && self.dimensions.lines.0 != 0
+            && self.dimensions.lines != 0
             && self.startup_mode != StartupMode::Maximized
         {
             Some(self.dimensions)
@@ -145,7 +145,7 @@ pub struct Dimensions {
     pub columns: Column,
 
     /// Window Height in character lines.
-    pub lines: Line,
+    pub lines: usize,
 }
 
 /// Window class hint.