From ecf24bdb7668a01e759050fff9d7ad74810863d5 Mon Sep 17 00:00:00 2001
From: Colomban Wendling <cwendling@hypra.fr>
Date: Wed, 23 Sep 2020 18:57:59 +0200
Subject: brightness applet: Prevent sliding from bogging down the UI

Do not perform a synchronous DBus call to update the brightness in real
time when the slider move, because at least on some hardware the call
is slow, which leads to the UI bogging down and looking frozen.

To fix this, cap the update rate in response to slider motion.  This
makes the brightness apply slightly slower, but prevent most bogging
down (if the rate is well chosen, at least).
---
 applets/brightness/brightness-applet.c | 38 ++++++++++++++++++++++++++++++++--
 1 file changed, 36 insertions(+), 2 deletions(-)

diff --git a/applets/brightness/brightness-applet.c b/applets/brightness/brightness-applet.c
index 240cff8..bf57320 100644
--- a/applets/brightness/brightness-applet.c
+++ b/applets/brightness/brightness-applet.c
@@ -62,6 +62,8 @@ typedef struct{
 	guint level;
 	/* a cache for panel size */
 	gint size;
+	/* the slider action delaying */
+	guint slider_delay_id;
 } GpmBrightnessApplet;
 
 typedef struct{
@@ -109,6 +111,11 @@ static void      gpm_applet_destroy_cb            (GtkWidget *widget);
 #define MATE_PANEL_APPLET_VERTICAL(p)					\
 	 (((p) == MATE_PANEL_APPLET_ORIENT_LEFT) || ((p) == MATE_PANEL_APPLET_ORIENT_RIGHT))
 
+/* The frequency (in milliseconds) at which update the brightness when the UI
+ * slider is moved.  A too short value might lead to freezing the UI, and a
+ * too long one will seem unresponsive. */
+#define GPM_BRIGHTNESS_APPLET_SLIDER_FREQUENCY	100
+
 /**
  * gpm_applet_get_brightness:
  * Return value: Success value, or zero for failure
@@ -433,6 +440,24 @@ gpm_applet_minus_cb (GtkWidget *w, GpmBrightnessApplet *applet)
 	return TRUE;
 }
 
+/**
+ * gpm_applet_slide_delayed_cb:
+ * @data: Brightness applet instance
+ *
+ * callback for the delayed slider changes, actually performing the DBus call
+ **/
+static gboolean
+gpm_applet_slide_delayed_cb (gpointer data)
+{
+	GpmBrightnessApplet *applet = data;
+
+	applet->call_worked = gpm_applet_set_brightness (applet);
+	gpm_applet_update_popup_level (applet);
+	applet->slider_delay_id = 0;
+
+	return FALSE;
+}
+
 /**
  * gpm_applet_slide_cb:
  * @widget: The sending widget (slider)
@@ -444,8 +469,11 @@ static gboolean
 gpm_applet_slide_cb (GtkWidget *w, GpmBrightnessApplet *applet)
 {
 	applet->level = gtk_range_get_value (GTK_RANGE(applet->slider));
-	applet->call_worked = gpm_applet_set_brightness (applet);
-	gpm_applet_update_popup_level (applet);
+	/* we delay applying the new value to improve reactivity, because the
+	 * DBus call might be slow (and we don't want to spam the bus either) */
+	if (! applet->slider_delay_id)
+		applet->slider_delay_id = g_timeout_add (GPM_BRIGHTNESS_APPLET_SLIDER_FREQUENCY,
+							 gpm_applet_slide_delayed_cb, applet);
 	return TRUE;
 }
 
@@ -847,6 +875,11 @@ gpm_applet_destroy_cb (GtkWidget *widget)
 {
 	GpmBrightnessApplet *applet = GPM_BRIGHTNESS_APPLET(widget);
 
+	if (applet->slider_delay_id) {
+		g_source_remove (applet->slider_delay_id);
+		applet->slider_delay_id = 0;
+	}
+
 	g_bus_unwatch_name (applet->bus_watch_id);
 	if (applet->icon != NULL)
 		g_object_unref (applet->icon);
@@ -973,6 +1006,7 @@ gpm_brightness_applet_init (GpmBrightnessApplet *applet)
 	applet->icon = NULL;
 	applet->connection = NULL;
 	applet->proxy = NULL;
+	applet->slider_delay_id = 0;
 
 	/* Add application specific icons to search path */
 	gtk_icon_theme_append_search_path (gtk_icon_theme_get_default (),
-- 
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