Fix freetype 26.6 format conversion

This resolves a rounding issue when converting to the 26.6 format used
by freetype for character sizes.

This rounding behavior is taken from cairo:
https://gitlab.freedesktop.org/cairo/cairo/-/blob/master/src/cairo-ft-font.c#L900-903

There are various different implementations of the F26Dot6 conversion
online, but the rounding that cairo does seems to be the most common.
Since cairo is very commonly used, it should produce good results
compared with the rest of Linux text rendering.

Fixes #2780.

Co-authored-by: Christian Duerr <contact@christianduerr.com>
Co-authored-by: Kirill Chibisov <contact@kchibisov.com>

CHANGELOG.md

@@ -71,6 +71,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - Fontconfig's `autohint` and `hinting` options being ignored
 - Ingoring of default FreeType properties
 - Alacritty crashing at startup when the configured font does not exist
+- Font size rounding error
 
 ### Removed
 

font/src/ft/mod.rs

@@ -86,7 +86,7 @@ pub struct FreeTypeRasterizer {
 
 #[inline]
 fn to_freetype_26_6(f: f32) -> isize {
-    ((1i32 << 6) as f32 * f) as isize
+    ((1i32 << 6) as f32 * f).round() as isize
 }
 
 #[inline]