Fix font spacing error

Fixes alacritty#2098.

CHANGELOG.md

@@ -4,6 +4,16 @@ All notable changes to this project will be documented in this file.
 The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
+## [Unreleased]
+
+### Changed
+
+- Accept fonts which are smaller in width or height than a single pixel
+
+### Fixed
+
+- Incorrect font spacing after moving Alacritty between displays
+
 ## Version 0.2.8
 
 ### Added

src/display.rs

@@ -43,9 +43,6 @@ pub enum Error {
 
     /// Error in renderer
     Render(renderer::Error),
-
-    /// Computed cell size is invalid
-    InvalidCellSize,
 }
 
 impl ::std::error::Error for Error {
@@ -54,7 +51,6 @@ impl ::std::error::Error for Error {
             Error::Window(ref err) => Some(err),
             Error::Font(ref err) => Some(err),
             Error::Render(ref err) => Some(err),
-            Error::InvalidCellSize => None,
         }
     }
 
@@ -63,19 +59,16 @@ impl ::std::error::Error for Error {
             Error::Window(ref err) => err.description(),
             Error::Font(ref err) => err.description(),
             Error::Render(ref err) => err.description(),
-            Error::InvalidCellSize => "cell size is invalid",
         }
     }
 }
 
 impl ::std::fmt::Display for Error {
     fn fmt(&self, f: &mut ::std::fmt::Formatter<'_>) -> ::std::fmt::Result {
-        use std::error::Error as StdError;
         match *self {
             Error::Window(ref err) => err.fmt(f),
             Error::Font(ref err) => err.fmt(f),
             Error::Render(ref err) => err.fmt(f),
-            Error::InvalidCellSize => write!(f, "{}", self.description()),
         }
     }
 }
@@ -262,45 +255,32 @@ impl Display {
         // Need font metrics to resize the window properly. This suggests to me the
         // font metrics should be computed before creating the window in the first
         // place so that a resize is not needed.
-        let (cell_width, cell_height) =
-            Self::compute_cell_size(&config, &glyph_cache.font_metrics())?;
+        let (cw, ch) = Self::compute_cell_size(config, &glyph_cache.font_metrics());
 
-        Ok((glyph_cache, cell_width, cell_height))
+        Ok((glyph_cache, cw, ch))
     }
 
-    fn compute_cell_size(config: &Config, metrics: &font::Metrics) -> Result<(f32, f32), Error> {
-        let cell_width =
-            ((metrics.average_advance + f64::from(config.font().offset().x)) as f32).floor();
-        let cell_height =
-            ((metrics.line_height + f64::from(config.font().offset().y)) as f32).floor();
-
-        if cell_width < 1. || cell_height < 1. {
-            return Err(Error::InvalidCellSize)
-        }
-
-        Ok((cell_width, cell_height))
-    }
-
-    pub fn update_glyph_cache(
-        &mut self,
-        config: &Config,
-        size: font::Size
-    ) -> Result<(), Error> {
-        let dpr = self.size_info.dpr;
+    pub fn update_glyph_cache(&mut self, config: &Config) {
         let cache = &mut self.glyph_cache;
-
-        let (cell_width, cell_height) = Self::compute_cell_size(config, &cache.font_metrics())?;
-
-        self.font_size = size;
+        let dpr = self.size_info.dpr;
+        let size = self.font_size;
 
         self.renderer.with_loader(|mut api| {
             let _ = cache.update_font_size(config.font(), size, dpr, &mut api);
         });
 
-        self.size_info.cell_width = cell_width;
-        self.size_info.cell_height = cell_height;
+        let (cw, ch) = Self::compute_cell_size(config, &cache.font_metrics());
+        self.size_info.cell_width = cw;
+        self.size_info.cell_height = ch;
+    }
 
-        Ok(())
+    fn compute_cell_size(config: &Config, metrics: &font::Metrics) -> (f32, f32) {
+        let offset_x = f64::from(config.font().offset().x);
+        let offset_y = f64::from(config.font().offset().y);
+        (
+            f32::max(1., ((metrics.average_advance + offset_x) as f32).floor()),
+            f32::max(1., ((metrics.line_height + offset_y) as f32).floor()),
+        )
     }
 
     #[inline]
@@ -346,13 +326,13 @@ impl Display {
                 ));
             }
 
+            self.font_size = terminal.font_size;
             self.last_message = terminal.message_buffer_mut().message();
             self.size_info.dpr = dpr;
         }
 
-        if font_changed && self.update_glyph_cache(config, terminal.font_size).is_err() {
-            // Revert the terminal font size back to last known good state
-            terminal.font_size = self.font_size;
+        if font_changed {
+            self.update_glyph_cache(config);
         }
 
         if let Some(psize) = new_size.take() {