xwayland: allow windows to scale themselves

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)
+}