On X11, cache the XRandR extension version

src/platform_impl/linux/x11/monitor.rs

@@ -234,7 +234,8 @@ impl XConnection {
 
     fn query_monitor_list(&self) -> Result<Vec<MonitorHandle>, X11Error> {
         let root = self.default_root();
-        let resources = ScreenResources::from_connection(self.xcb_connection(), root)?;
+        let resources =
+            ScreenResources::from_connection(self.xcb_connection(), root, self.randr_version())?;
 
         // Pipeline all of the get-crtc requests.
         let mut crtc_cookies = Vec::with_capacity(resources.crtcs().len());
@@ -343,10 +344,9 @@ impl ScreenResources {
     pub(crate) fn from_connection(
         conn: &impl x11rb::connection::Connection,
         root: &x11rb::protocol::xproto::Screen,
+        (major_version, minor_version): (u32, u32),
     ) -> Result<Self, X11Error> {
-        let version = conn.randr_query_version(1, 3)?.reply()?;
-
-        if (version.major_version == 1 && version.minor_version >= 3) || version.major_version > 1 {
+        if (major_version == 1 && minor_version >= 3) || major_version > 1 {
             let reply = conn
                 .randr_get_screen_resources_current(root.root)?
                 .reply()?;

src/platform_impl/linux/x11/xdisplay.rs

@@ -11,7 +11,12 @@ use std::{
 use crate::window::CursorIcon;
 
 use super::{atoms::Atoms, ffi, monitor::MonitorHandle};
-use x11rb::{connection::Connection, protocol::xproto, resource_manager, xcb_ffi::XCBConnection};
+use x11rb::{
+    connection::Connection,
+    protocol::{randr::ConnectionExt as _, xproto},
+    resource_manager,
+    xcb_ffi::XCBConnection,
+};
 
 /// A connection to an X server.
 pub(crate) struct XConnection {
@@ -47,6 +52,9 @@ pub(crate) struct XConnection {
     /// The resource database.
     database: RwLock<resource_manager::Database>,
 
+    /// RandR version.
+    randr_version: (u32, u32),
+
     pub latest_error: Mutex<Option<XError>>,
     pub cursor_cache: Mutex<HashMap<Option<CursorIcon>, ffi::Cursor>>,
 }
@@ -104,6 +112,13 @@ impl XConnection {
         let database = resource_manager::new_from_default(&xcb)
             .map_err(|e| XNotSupported::XcbConversionError(Arc::new(e)))?;
 
+        // Load the RandR version.
+        let randr_version = xcb
+            .randr_query_version(1, 3)
+            .expect("failed to request XRandR version")
+            .reply()
+            .expect("failed to query XRandR version");
+
         Ok(XConnection {
             xlib,
             xcursor,
@@ -117,6 +132,7 @@ impl XConnection {
             monitor_handles: Mutex::new(None),
             database: RwLock::new(database),
             cursor_cache: Default::default(),
+            randr_version: (randr_version.major_version, randr_version.minor_version),
         })
     }
 
@@ -131,6 +147,11 @@ impl XConnection {
         }
     }
 
+    #[inline]
+    pub fn randr_version(&self) -> (u32, u32) {
+        self.randr_version
+    }
+
     /// Get the underlying XCB connection.
     #[inline]
     pub fn xcb_connection(&self) -> &XCBConnection {