x11: query Xft.dpi from the root window

We should now be using the root window specified default dpi
if the dpi is left unspecified in the wezterm configuration.

refs: #515

wezterm-font/src/lib.rs

@@ -8,6 +8,7 @@ use std::cell::RefCell;
 use std::collections::{HashMap, HashSet};
 use std::rc::{Rc, Weak};
 use wezterm_term::CellAttributes;
+use window::default_dpi;
 
 mod hbwrap;
 
@@ -295,7 +296,7 @@ impl FontConfigInner {
 
         let font_size = config.font_size * *self.font_scale.borrow();
         let dpi =
-            *self.dpi_scale.borrow() as u32 * config.dpi.unwrap_or(::window::DEFAULT_DPI) as u32;
+            *self.dpi_scale.borrow() as u32 * config.dpi.unwrap_or_else(|| default_dpi()) as u32;
         let metrics = shaper.metrics(font_size, dpi).with_context(|| {
             format!(
                 "obtaining metrics for font_size={} @ dpi {}",

wezterm-gui/src/termwindow/mod.rs

@@ -462,7 +462,7 @@ impl TermWindow {
             pixel_height: ((rows_with_tab_bar * render_metrics.cell_size.height as u16)
                 + config.window_padding.top
                 + config.window_padding.bottom) as usize,
-            dpi: config.dpi.unwrap_or(::window::DEFAULT_DPI) as usize,
+            dpi: config.dpi.unwrap_or_else(|| ::window::default_dpi()) as usize,
         };
 
         log::trace!(

wezterm-gui/src/termwindow/resize.rs

@@ -31,7 +31,7 @@ impl super::TermWindow {
 
         let (prior_font, prior_dpi) = self
             .fonts
-            .change_scaling(font_scale, dimensions.dpi as f64 / ::window::DEFAULT_DPI);
+            .change_scaling(font_scale, dimensions.dpi as f64 / ::window::default_dpi());
         match RenderMetrics::new(&self.fonts) {
             Ok(metrics) => {
                 self.render_metrics = metrics;
@@ -233,7 +233,7 @@ impl super::TermWindow {
             pixel_height: ((rows_with_tab_bar * render_metrics.cell_size.height as u16)
                 + config.window_padding.top
                 + config.window_padding.bottom) as usize,
-            dpi: config.dpi.unwrap_or(::window::DEFAULT_DPI) as usize,
+            dpi: config.dpi.unwrap_or_else(|| ::window::default_dpi()) as usize,
         };
 
         self.apply_scale_change(&dimensions, 1.0);

window/src/connection.rs

@@ -22,6 +22,10 @@ pub trait ConnectionOps {
         res
     }
 
+    fn default_dpi(&self) -> f64 {
+        crate::DEFAULT_DPI
+    }
+
     fn init() -> Fallible<Rc<Connection>> {
         let conn = Rc::new(Connection::create_new()?);
         CONN.with(|m| *m.borrow_mut() = Some(Rc::clone(&conn)));

window/src/lib.rs

@@ -11,9 +11,16 @@ mod timerlist;
 use configuration::{config, WindowConfigHandle};
 
 #[cfg(target_os = "macos")]
-pub const DEFAULT_DPI: f64 = 72.0;
+pub(crate) const DEFAULT_DPI: f64 = 72.0;
 #[cfg(not(target_os = "macos"))]
-pub const DEFAULT_DPI: f64 = 96.0;
+pub(crate) const DEFAULT_DPI: f64 = 96.0;
+
+pub fn default_dpi() -> f64 {
+    match Connection::get() {
+        Some(conn) => conn.default_dpi(),
+        None => DEFAULT_DPI,
+    }
+}
 
 mod egl;
 

window/src/os/x11/connection.rs

@@ -17,6 +17,7 @@ use xcb_util::ffi::keysyms::{xcb_key_symbols_alloc, xcb_key_symbols_free, xcb_ke
 
 pub struct XConnection {
     pub conn: xcb_util::ewmh::Connection,
+    pub default_dpi: f64,
     pub screen_num: i32,
     pub root: xcb::xproto::Window,
     pub keyboard: Keyboard,
@@ -177,6 +178,10 @@ impl ConnectionOps for XConnection {
         *self.should_terminate.borrow_mut() = true;
     }
 
+    fn default_dpi(&self) -> f64 {
+        self.default_dpi
+    }
+
     fn run_message_loop(&self) -> anyhow::Result<()> {
         self.conn.flush();
 
@@ -394,9 +399,17 @@ impl XConnection {
 
         let xrm =
             crate::x11::xrm::parse_root_resource_manager(&conn, root).unwrap_or(HashMap::new());
+        let default_dpi = xrm
+            .get("Xft.dpi")
+            .as_ref()
+            .map(|s| s.as_str())
+            .unwrap_or("96")
+            .parse::<f64>()
+            .unwrap_or(crate::DEFAULT_DPI);
 
         let conn = XConnection {
             conn,
+            default_dpi,
             cursor_font_id,
             screen_num,
             root,

window/src/os/x11/window.rs

@@ -188,7 +188,7 @@ impl XWindowInner {
                     Dimensions {
                         pixel_width: self.width as usize,
                         pixel_height: self.height as usize,
-                        dpi: crate::DEFAULT_DPI as usize,
+                        dpi: conn.default_dpi as usize,
                     },
                     self.is_fullscreen().unwrap_or(false),
                 )