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, 2 insertions, 2 deletions

diff --git a/alacritty_terminal/src/term/cell.rs b/alacritty_terminal/src/term/cell.rs
index 91ee3391..255cbce7 100644
--- a/alacritty_terminal/src/term/cell.rs
+++ b/alacritty_terminal/src/term/cell.rs
@@ -178,7 +178,7 @@ mod tests {
 
     #[test]
     fn line_length_works() {
-        let mut row = Row::<Cell>::new(Column(10));
+        let mut row = Row::<Cell>::new(10);
         row[Column(5)].c = 'a';
 
         assert_eq!(row.line_length(), Column(6));
@@ -186,7 +186,7 @@ mod tests {
 
     #[test]
     fn line_length_works_with_wrapline() {
-        let mut row = Row::<Cell>::new(Column(10));
+        let mut row = Row::<Cell>::new(10);
         row[Column(9)].flags.insert(super::Flags::WRAPLINE);
 
         assert_eq!(row.line_length(), Column(10));