Unthrottle windows in screencopy sessions

If an individual window was being screencast, and that window was not
visible, for example because it was minimized, that window would only
be rendered every 995ms, which did not look good on the screencast.

Now, non-visible windows with active screencopy sessions, as well as
windows that are mapped on non-visible workspaces with active
screencopy sessions, are rendered every 1/60th of a second, which
matches the frame rate of the video produced by
xdg-desktop-portal-cosmic.  In future, it might be good to let
screencopy clients suggest a redraw rate for captured windows.

src/state.rs

@@ -11,6 +11,7 @@ use crate::{
     input::{gestures::GestureState, PointerFocusState},
     shell::{grabs::SeatMoveGrabState, CosmicSurface, SeatExt, Shell},
     utils::prelude::OutputExt,
+    wayland::handlers::screencopy::SessionHolder,
     wayland::protocols::{
         atspi::AtspiState,
         drm::WlDrmState,
@@ -108,6 +109,7 @@ use time::UtcOffset;
 
 use std::{
     cell::RefCell,
+    cmp::min,
     collections::HashSet,
     ffi::OsString,
     process::Child,
@@ -935,7 +937,17 @@ impl Common {
                 None
             }
         };
-        let throttle = Some(Duration::from_millis(995));
+        const THROTTLE: Option<Duration> = Some(Duration::from_millis(995));
+        const SCREENCOPY_THROTTLE: Option<Duration> = Some(Duration::from_nanos(16_666_666));
+
+        fn throttle(session_holder: &impl SessionHolder) -> Option<Duration> {
+            if session_holder.sessions().is_empty() && session_holder.cursor_sessions().is_empty() {
+                THROTTLE
+            } else {
+                SCREENCOPY_THROTTLE
+            }
+        }
+
         let shell = self.shell.read().unwrap();
 
         if let Some(session_lock) = shell.session_lock.as_ref() {
@@ -982,7 +994,7 @@ impl Common {
             if let Some(move_grab) = seat.user_data().get::<SeatMoveGrabState>() {
                 if let Some(grab_state) = move_grab.lock().unwrap().as_ref() {
                     for (window, _) in grab_state.element().windows() {
-                        window.send_frame(output, time, throttle, should_send);
+                        window.send_frame(output, time, throttle(&window), should_send);
                     }
                 }
             }
@@ -997,21 +1009,21 @@ impl Common {
             .mapped()
             .for_each(|mapped| {
                 for (window, _) in mapped.windows() {
-                    window.send_frame(output, time, throttle, should_send);
+                    window.send_frame(output, time, throttle(&window), should_send);
                 }
             });
 
         let active = shell.active_space(output);
         active.mapped().for_each(|mapped| {
             for (window, _) in mapped.windows() {
-                window.send_frame(output, time, throttle, should_send);
+                window.send_frame(output, time, throttle(&window), should_send);
             }
         });
 
         // other (throttled) windows
         active.minimized_windows.iter().for_each(|m| {
             for (window, _) in m.window.windows() {
-                window.send_frame(output, time, throttle, |_, _| None);
+                window.send_frame(output, time, throttle(&window), |_, _| None);
             }
         });
         for space in shell
@@ -1021,25 +1033,26 @@ impl Common {
         {
             space.mapped().for_each(|mapped| {
                 for (window, _) in mapped.windows() {
+                    let throttle = min(throttle(space), throttle(&window));
                     window.send_frame(output, time, throttle, |_, _| None);
                 }
             });
             space.minimized_windows.iter().for_each(|m| {
                 for (window, _) in m.window.windows() {
-                    window.send_frame(output, time, throttle, |_, _| None);
+                    window.send_frame(output, time, throttle(&window), |_, _| None);
                 }
             })
         }
 
         shell.override_redirect_windows.iter().for_each(|or| {
             if let Some(wl_surface) = or.wl_surface() {
-                send_frames_surface_tree(&wl_surface, output, time, throttle, should_send);
+                send_frames_surface_tree(&wl_surface, output, time, THROTTLE, should_send);
             }
         });
 
         let map = smithay::desktop::layer_map_for_output(output);
         for layer_surface in map.layers() {
-            layer_surface.send_frame(output, time, throttle, should_send);
+            layer_surface.send_frame(output, time, THROTTLE, should_send);
         }
     }
 }