display

modules/applications/niri/home.nix

@@ -185,9 +185,38 @@ in
         default-window-height.fixed = 920;
       }
       {
-        # Keep Zoom Workplace and meeting windows tiled, but let meeting
-        # controls, screen-share toolbars, and other auxiliary Zoom windows be
-        # positioned freely.
+        # Zoom presents these two fixed-size primary windows. Explicitly keep
+        # them tiled, overriding Niri's automatic fixed-size-window floating.
+        matches = [
+          {
+            app-id = "^(?i:zoom)$";
+            title = "^(?i:zoom workplace)$";
+          }
+          {
+            app-id = "^(?i:zoom)$";
+            title = "^ミーティング$";
+          }
+        ];
+        open-floating = false;
+      }
+      {
+        # Zoom's screen-share controls are a toolbar, so open them where the
+        # client expects them rather than in the middle of the workspace.
+        matches = [
+          {
+            app-id = "^(?i:zoom)$";
+            title = "^as_toolbar$";
+          }
+        ];
+        open-floating = true;
+        default-floating-position = {
+          x = 0;
+          y = 8;
+          relative-to = "top";
+        };
+      }
+      {
+        # Keep all other Zoom auxiliary windows freely positionable.
         matches = [ { app-id = "^(?i:zoom)$"; } ];
         excludes = [
           { title = "^(?i:zoom workplace)$"; }

modules/applications/niri/nixos.nix

@@ -1,4 +1,9 @@
 { config, pkgs, ... }:
+let
+  wdisplays = pkgs.wdisplays.overrideAttrs (oldAttrs: {
+    patches = (oldAttrs.patches or [ ]) ++ [ ./wdisplays-canonical-scale.patch ];
+  });
+in
 {
   programs.niri.enable = true;
 
@@ -6,8 +11,10 @@
   # user units with NixOS. Without this, Ly cannot start niri-session.
   systemd.packages = [ config.programs.niri.package ];
 
-  environment.systemPackages = with pkgs; [
-    wdisplays # Wayland display configuration GUI
-    wlr-randr # Wayland output management CLI
+  environment.systemPackages = [
+    # Keep the transient Wayland-native GUI, with fractional scales rounded to
+    # the same wl_fixed_t value that niri receives on the first Apply.
+    wdisplays
+    pkgs.wlr-randr # Wayland output management CLI
   ];
 }

modules/applications/niri/wdisplays-canonical-scale.patch

@@ -0,0 +1,22 @@
+diff --git a/src/headform.c b/src/headform.c
+--- a/src/headform.c
++++ b/src/headform.c
+@@ -39,1 +39,8 @@
++/* The output-management protocol transmits scale as a Wayland 24.8 fixed
++ * point value. Use that same value for preview geometry so a fractional scale
++ * cannot change underneath positions during the first apply. */
++static double canonicalize_scale(double scale) {
++  return wl_fixed_to_double(wl_fixed_from_double(scale));
++}
++
+ static void head_form_update_sensitivity(WdHeadForm *form) {
+@@ -359,2 +366,3 @@ void wd_head_form_fill_config(WdHeadForm *form, struct wd_head_config *output) {
+-  output->scale = gtk_spin_button_get_value(GTK_SPIN_BUTTON(priv->scale));
++  output->scale = canonicalize_scale(
++      gtk_spin_button_get_value(GTK_SPIN_BUTTON(priv->scale)));
+   output->x = gtk_spin_button_get_value(GTK_SPIN_BUTTON(priv->pos_x));
+@@ -385,2 +393,3 @@ void wd_head_form_get_dimensions(WdHeadForm *form, WdHeadDimensions *dimensions)
+-  dimensions->scale = gtk_spin_button_get_value(GTK_SPIN_BUTTON(priv->scale));
++  dimensions->scale = canonicalize_scale(
++      gtk_spin_button_get_value(GTK_SPIN_BUTTON(priv->scale)));
+   dimensions->rotation_id = g_variant_get_int32(g_action_get_state(priv->rotate_action)) / 90;