screenshot: Fix slow audiovisual feedback on when taking screenshot

Add a "screenshot-taken" signal from the screenshot service's internal C
implementation, and use that to trigger the camera flash visual effect
and the click sound, allowing them to run in parallel with the PNG
compression instead of waiting until the file is complete to start.

This significantly improves perceived latency on high res setups such as
4K, 5K, or dual 4K screens.

Fixes https://gitlab.gnome.org/GNOME/gnome-shell/-/issues/512

Co-authored-by: Brion Vibber <bvibber@wikimedia.org>
Part-of: <https://gitlab.gnome.org/GNOME/gnome-shell/-/merge_requests/1658>

js/ui/screenshot.js

@@ -131,16 +131,19 @@ var ScreenshotService = class {
         return [null, null];
     }
 
-    _onScreenshotComplete(area, stream, file, flash, invocation) {
+    _flashAsync(shooter) {
-        if (flash) {
+        return new Promise((resolve, _reject) => {
-            let flashspot = new Flashspot(area);
+            shooter.connect('screenshot_taken', (s, area) => {
-            flashspot.fire(() => {
+                const flashspot = new Flashspot(area);
-                this._removeShooterForSender(invocation.get_sender());
+                flashspot.fire(resolve);
+
+                global.display.get_sound_player().play_from_theme(
+                    'screen-capture', _('Screenshot taken'), null);
+            });
         });
-        } else {
-            this._removeShooterForSender(invocation.get_sender());
     }
 
+    _onScreenshotComplete(stream, file, invocation) {
         stream.close(null);
 
         let filenameUsed = '';
@@ -192,9 +195,12 @@ var ScreenshotService = class {
             return;
 
         try {
-            let [area] =
+            await Promise.all([
-                await screenshot.screenshot_area(x, y, width, height, stream);
+                flash ? this._flashAsync(screenshot) : null,
-            this._onScreenshotComplete(area, stream, file, flash, invocation);
+                screenshot.screenshot_area(x, y, width, height, stream),
+            ]);
+            this._onScreenshotComplete(stream, file, invocation);
+            this._removeShooterForSender(invocation.get_sender());
         } catch (e) {
             this._removeShooterForSender(invocation.get_sender());
             invocation.return_value(new GLib.Variant('(bs)', [false, '']));
@@ -212,9 +218,12 @@ var ScreenshotService = class {
             return;
 
         try {
-            let [area] =
+            await Promise.all([
-                await screenshot.screenshot_window(includeFrame, includeCursor, stream);
+                flash ? this._flashAsync(screenshot) : null,
-            this._onScreenshotComplete(area, stream, file, flash, invocation);
+                screenshot.screenshot_window(includeFrame, includeCursor, stream),
+            ]);
+            this._onScreenshotComplete(stream, file, invocation);
+            this._removeShooterForSender(invocation.get_sender());
         } catch (e) {
             this._removeShooterForSender(invocation.get_sender());
             invocation.return_value(new GLib.Variant('(bs)', [false, '']));
@@ -232,8 +241,12 @@ var ScreenshotService = class {
             return;
 
         try {
-            let [area] = await screenshot.screenshot(includeCursor, stream);
+            await Promise.all([
-            this._onScreenshotComplete(area, stream, file, flash, invocation);
+                flash ? this._flashAsync(screenshot) : null,
+                screenshot.screenshot(includeCursor, stream),
+            ]);
+            this._onScreenshotComplete(stream, file, invocation);
+            this._removeShooterForSender(invocation.get_sender());
         } catch (e) {
             this._removeShooterForSender(invocation.get_sender());
             invocation.return_value(new GLib.Variant('(bs)', [false, '']));

po/POTFILES.in

@@ -47,6 +47,7 @@ js/ui/panel.js
 js/ui/popupMenu.js
 js/ui/runDialog.js
 js/ui/screenShield.js
+js/ui/screenshot.js
 js/ui/search.js
 js/ui/shellEntry.js
 js/ui/shellMountOperation.js

src/shell-screenshot.c

@@ -25,6 +25,15 @@ typedef enum _ShellScreenshotMode
   SHELL_SCREENSHOT_AREA,
 } ShellScreenshotMode;
 
+enum
+{
+  SCREENSHOT_TAKEN,
+
+  LAST_SIGNAL
+};
+
+static guint signals[LAST_SIGNAL] = { 0, };
+
 typedef struct _ShellScreenshotPrivate  ShellScreenshotPrivate;
 
 struct _ShellScreenshot
@@ -55,7 +64,15 @@ G_DEFINE_TYPE_WITH_PRIVATE (ShellScreenshot, shell_screenshot, G_TYPE_OBJECT);
 static void
 shell_screenshot_class_init (ShellScreenshotClass *screenshot_class)
 {
-  (void) screenshot_class;
+  signals[SCREENSHOT_TAKEN] =
+    g_signal_new ("screenshot-taken",
+                  G_TYPE_FROM_CLASS(screenshot_class),
+                  G_SIGNAL_RUN_LAST,
+                  0,
+                  NULL, NULL, NULL,
+                  G_TYPE_NONE,
+                  1,
+                  META_TYPE_RECTANGLE);
 }
 
 static void
@@ -321,6 +338,8 @@ grab_window_screenshot (ShellScreenshot     *screenshot,
       draw_cursor_image (priv->image, priv->screenshot_area);
     }
 
+  g_signal_emit (screenshot, signals[SCREENSHOT_TAKEN], 0, &rect);
+
   task = g_task_new (screenshot, NULL, on_screenshot_written, result);
   g_task_run_in_thread (task, write_screenshot_thread);
   g_object_unref (task);
@@ -372,6 +391,9 @@ on_after_paint (ClutterStage     *stage,
       grab_screenshot (screenshot, priv->flags, result);
     }
 
+  g_signal_emit (screenshot, signals[SCREENSHOT_TAKEN], 0,
+                 (cairo_rectangle_int_t *) &priv->screenshot_area);
+
   meta_enable_unredirect_for_display (display);
 }
 
@@ -430,6 +452,9 @@ shell_screenshot_screenshot (ShellScreenshot     *screenshot,
   if (meta_is_wayland_compositor ())
     {
       grab_screenshot (screenshot, flags, result);
+
+      g_signal_emit (screenshot, signals[SCREENSHOT_TAKEN], 0,
+                     (cairo_rectangle_int_t *) &priv->screenshot_area);
     }
   else
     {
@@ -540,6 +565,9 @@ shell_screenshot_screenshot_area (ShellScreenshot     *screenshot,
                           priv->screenshot_area.height,
                           SHELL_SCREENSHOT_FLAG_NONE);
 
+      g_signal_emit (screenshot, signals[SCREENSHOT_TAKEN], 0,
+                     (cairo_rectangle_int_t *) &priv->screenshot_area);
+
       task = g_task_new (screenshot, NULL, on_screenshot_written, result);
       g_task_run_in_thread (task, write_screenshot_thread);
     }