fonts: align emoji fonts with the primary font baseline

refs: #1203

docs/changelog.md

@@ -56,6 +56,7 @@ As features stabilize some brief notes about them will accumulate here.
 * Improved: [use_cap_height_to_scale_fallback_fonts](config/lua/config/use_cap_height_to_scale_fallback_fonts.md) now computes *cap-height* based on the rasterized glyph bitmap which means that the data is accurate in more cases, including for bitmap fonts.  Scaling is now also applied across varying text styles; previously it only applied to a font within an `wezterm.font_with_fallback` font list.
 * Fixed: ssh config parser incorrectly split `Host` patterns with commas instead of whitespace [#1196](https://github.com/wez/wezterm/issues/1196)
 * Fixed: search now auto-updates when the pane content changes [#1205](https://github.com/wez/wezterm/issues/1205)
+* Fixed: fonts with emoji presentation are shifted to better align with the primary font baseline [#1203](https://github.com/wez/wezterm/issues/1203)
 
 ### 20210814-124438-54e29167
 

wezterm-font/src/shaper/allsorts.rs

@@ -229,6 +229,7 @@ impl AllsortsParsedFont {
             cap_height_ratio: None,
             cap_height: None,
             is_scaled: true, // FIXME
+            presentation: Presentation::Text,
         };
 
         log::trace!("metrics: {:?}", metrics);

wezterm-font/src/shaper/harfbuzz.rs

@@ -473,6 +473,7 @@ impl FontShaper for HarfbuzzShaper {
             cap_height_ratio: selected_size.cap_height_to_height_ratio,
             cap_height: selected_size.cap_height.map(PixelLength::new),
             is_scaled: selected_size.is_scaled,
+            presentation: pair.presentation,
         };
 
         self.metrics.borrow_mut().insert(key, metrics.clone());

wezterm-font/src/shaper/mod.rs

@@ -1,5 +1,6 @@
 use crate::parser::ParsedFont;
 use crate::units::PixelLength;
+use termwiz::cell::Presentation;
 
 pub mod allsorts;
 pub mod harfbuzz;
@@ -60,6 +61,8 @@ pub struct FontMetrics {
     /// False if the font only has bitmap strikes and what we
     /// have here is a best approximation.
     pub is_scaled: bool,
+
+    pub presentation: Presentation,
 }
 
 pub trait FontShaper {

wezterm-gui/src/glyphcache.rs

@@ -20,6 +20,7 @@ use std::convert::TryInto;
 use std::rc::Rc;
 use std::sync::{Arc, MutexGuard};
 use std::time::Instant;
+use termwiz::cell::Presentation;
 use termwiz::color::RgbColor;
 use termwiz::image::{ImageData, ImageDataType};
 use termwiz::surface::CursorShape;
@@ -470,6 +471,23 @@ impl<T: Texture2d> GlyphCache<T> {
             }
         };
 
+        let descender_adjust = {
+            if info.font_idx == 0 {
+                PixelLength::new(0.0)
+            } else {
+                let descender = idx_metrics.descender * scale;
+                base_metrics.descender
+                    - descender
+                    - if idx_metrics.presentation == Presentation::Emoji {
+                        // If it's emoji, we'll just shift up to make
+                        // it sit on the baseline
+                        base_metrics.descender
+                    } else {
+                        PixelLength::new(0.0)
+                    }
+            }
+        };
+
         let (cell_width, cell_height) = (base_metrics.cell_width, base_metrics.cell_height);
 
         let glyph = if glyph.width == 0 || glyph.height == 0 {
@@ -482,7 +500,7 @@ impl<T: Texture2d> GlyphCache<T> {
                 y_offset: info.y_offset * scale,
                 x_advance: info.x_advance * scale,
                 bearing_x: PixelLength::zero(),
-                bearing_y: PixelLength::zero(),
+                bearing_y: descender_adjust,
                 scale,
             }
         } else {
@@ -494,7 +512,7 @@ impl<T: Texture2d> GlyphCache<T> {
             );
 
             let bearing_x = glyph.bearing_x * scale;
-            let bearing_y = glyph.bearing_y * scale;
+            let bearing_y = descender_adjust + (glyph.bearing_y * scale);
             let x_offset = info.x_offset * scale;
             let y_offset = info.y_offset * scale;
             let x_advance = info.x_advance * scale;