xwayland: allow windows to scale themselves

jay-config/src/_private/client.rs

@@ -27,6 +27,7 @@ use {
             connector_type::{ConnectorType, CON_UNKNOWN},
             Connector, DrmDevice, Format, GfxApi, Mode, TearingMode, Transform, VrrMode,
         },
+        xwayland::XScalingMode,
         Axis, Direction, ModifiedKeySym, PciId, Workspace,
     },
     bincode::Options,
@@ -816,6 +817,10 @@ impl Client {
         (width, height)
     }
 
+    pub fn set_x_scaling_mode(&self, mode: XScalingMode) {
+        self.send(&ClientMessage::SetXScalingMode { mode })
+    }
+
     pub fn set_vrr_mode(&self, connector: Option<Connector>, mode: VrrMode) {
         self.send(&ClientMessage::SetVrrMode { connector, mode })
     }

jay-config/src/_private/ipc.rs

@@ -14,6 +14,7 @@ use {
         },
         Axis, Direction, PciId, Workspace,
         _private::{PollableId, WireMode},
+        xwayland::XScalingMode,
     },
     serde::{Deserialize, Serialize},
     std::time::Duration,
@@ -523,6 +524,9 @@ pub enum ClientMessage<'a> {
     SetUiDragThreshold {
         threshold: i32,
     },
+    SetXScalingMode {
+        mode: XScalingMode,
+    },
 }
 
 #[derive(Serialize, Deserialize, Debug)]

jay-config/src/lib.rs

@@ -66,6 +66,7 @@ pub mod tasks;
 pub mod theme;
 pub mod timer;
 pub mod video;
+pub mod xwayland;
 
 /// A planar direction.
 #[derive(Serialize, Deserialize, Copy, Clone, Debug, Eq, PartialEq)]

jay-config/src/xwayland.rs

@@ -0,0 +1,33 @@
+//! Tools for configuring Xwayland.
+
+use serde::{Deserialize, Serialize};
+
+/// The scaling mode of X windows.
+#[derive(Serialize, Deserialize, Copy, Clone, Debug, Eq, PartialEq, Hash, Default)]
+pub struct XScalingMode(pub u32);
+
+impl XScalingMode {
+    /// The default mode.
+    ///
+    /// Currently this means that windows are rendered at the lowest scale and then
+    /// upscaled if necessary.
+    pub const DEFAULT: Self = Self(0);
+    /// Windows are rendered at the highest integer scale and then downscaled.
+    ///
+    /// This has significant performance implications unless the window is running on the
+    /// output with the highest scale and that scale is an integer scale.
+    ///
+    /// For example, on a 3840x2160 output with a 1.5 scale, a fullscreen window will be
+    /// rendered at 3840x2160 * 2 / 1.5 = 5120x2880 pixels and then downscaled to
+    /// 3840x2160. This overhead gets worse the lower the scale of the output is.
+    ///
+    /// Additionally, this mode requires the X window to scale its contents itself. In the
+    /// example above, you might achieve this by setting the environment variable
+    /// `GDK_SCALE=2`.
+    pub const DOWNSCALED: Self = Self(1);
+}
+
+/// Sets the scaling mode for X windows.
+pub fn set_x_scaling_mode(mode: XScalingMode) {
+    get!().set_x_scaling_mode(mode)
+}