config: add line_height config option

The default is 1.0.  `line_height` is used to scale the effective
cell height, increasing the amount of space between font baselines.

refs: https://github.com/wez/wezterm/discussions/387

config/src/lib.rs

@@ -460,6 +460,9 @@ pub struct Config {
     #[serde(default = "default_font_size")]
     pub font_size: f64,
 
+    #[serde(default = "default_one_point_oh_f64")]
+    pub line_height: f64,
+
     #[serde(default)]
     pub allow_square_glyphs_to_overflow_width: AllowSquareGlyphOverflow,
 
@@ -827,6 +830,10 @@ pub struct Config {
     pub enable_csi_u_key_encoding: bool,
 }
 
+fn default_one_point_oh_f64() -> f64 {
+    1.0
+}
+
 fn default_one_point_oh() -> f32 {
     1.0
 }

docs/changelog.markdown

@@ -28,6 +28,7 @@ brief notes about them may accumulate here.
 * Revised pty output processing and removed the related `ratelimit_output_bytes_per_second` option
 * Workaround Cocoa leaking window position saved state file descriptors to child processes on macOS Big Sur
 * The 256 color cube now uses slightly brighter colors [#348](https://github.com/wez/wezterm/issues/348)
+* New: added `line_height` configuration option to scale the computed cell height. The default is `1.0`, resulting in using the font-specified metrics. Setting it to `1.2` will result in a 20% larger cell height.
 
 ### 20201101-103216-403d002d
 

docs/config/fonts.markdown

@@ -28,6 +28,15 @@ return {
   -- emulators, you may wish to tune this value!
   dpi = 96.0,
 
+  -- (available in nightly builds)
+  -- Scale the effective cell height.
+  -- The cell height is computed based on your selected font_size
+  -- and dpi and then multiplied by line_height.  Setting it to
+  -- eg: 1.2 will result in the spacing between lines being 20%
+  -- larger than the distance specified by the font author.
+  -- Setting it to eg: 0.9 will make it 10% smaller.
+  line_height = 1.0,
+
   -- When true (the default), text that is set to ANSI color
   -- indices 0-7 will be shifted to the corresponding brighter
   -- color index (8-15) when the intensity is set to Bold.

wezterm-gui/src/gui/utilsprites.rs

@@ -2,6 +2,7 @@ use super::glyphcache::GlyphCache;
 use ::window::bitmaps::atlas::{OutOfTextureSpace, Sprite};
 use ::window::bitmaps::{BitmapImage, Image, Texture2d};
 use ::window::*;
+use config::configuration;
 use std::rc::Rc;
 use termwiz::surface::CursorShape;
 use wezterm_font::units::*;
@@ -24,8 +25,10 @@ impl RenderMetrics {
             .default_font_metrics()
             .expect("failed to get font metrics!?");
 
+        let line_height = configuration().line_height;
+
         let (cell_height, cell_width) = (
-            metrics.cell_height.get().ceil() as usize,
+            (metrics.cell_height.get() * line_height).ceil() as usize,
             metrics.cell_width.get().ceil() as usize,
         );