gui: fix initial pixel geometry on hidpi displays

refs: #1387

docs/changelog.md

@@ -27,6 +27,7 @@ As features stabilize some brief notes about them will accumulate here.
 * Improved conformance of CUP, HVP, SLRM, STBM escape sequences by support empty first parameter. Thanks to [@ninjalj](https://github.com/ninjalj)! [#1377](https://github.com/wez/wezterm/pull/1377)
 * tab bar didn't correctly handle double-wide cells and could truncate at edges when using `format-tab-title` [#1371](https://github.com/wez/wezterm/issues/1371)
 * `wezterm cli --no-auto-start` was not respected
+* Pixel geometry configured on the PTY in new windows could be incorrect on HiDPI displays until the window was resized [#1387](https://github.com/wez/wezterm/issues/1387)
 
 ### 20211205-192649-672c1cc1
 

wezterm-gui/src/termwindow/mod.rs

@@ -550,6 +550,23 @@ impl TermWindow {
             pixel_height: (render_metrics.cell_size.height as usize * physical_rows) as u16,
         };
 
+        if terminal_size != size {
+            // DPI is different from the default assumed DPI when the mux
+            // created the pty. We need to inform the kernel of the revised
+            // pixel geometry now
+            log::trace!(
+                "Initial geometry was {:?} but dpi-adjusted geometry \
+                        is {:?}; update the kernel pixel geometry for the ptys!",
+                terminal_size,
+                size
+            );
+            if let Some(window) = mux.get_window(mux_window_id) {
+                for tab in window.iter() {
+                    tab.resize(size);
+                }
+            };
+        }
+
         let h_context = DimensionContext {
             dpi: dpi as f32,
             pixel_max: terminal_size.pixel_width as f32,

window/src/os/x11/connection.rs

@@ -470,6 +470,7 @@ impl XConnection {
         log::trace!("xsettings are {:?}", xsettings);
 
         let default_dpi = RefCell::new(compute_default_dpi(&xrm, &xsettings));
+        log::trace!("computed initial dpi: {:?}", default_dpi);
 
         xcb_imdkit::ImeClient::set_logger(|msg| log::debug!("Ime: {}", msg));
         let ime = unsafe {