[gimp/gimp-2-10] app: add back a timeout-based idle function to queue a canvas redraw.

[Jehan <jehanp src gnome org>]

commit 71b23da329223ab765ecf855efbb3adc82ede7d6
Author: Jehan <jehan girinstud io>
Date:   Tue May 11 19:11:30 2021 +0200

    app: add back a timeout-based idle function to queue a canvas redraw.
    
    I'm still very unclear why exactly but it would seem that just queuing
    the redraw with an idle function is not enough. At least on Windows,
    Jacob was having cases where opening an image would get stuck unless the
    mouse was moved (causing draw events most likely).
    
    So let's use a timeout function instead. Probably no need to queue the
    idle followed by the timeout function as we had before commit
    4fee04b839. Instead just directly queue a draw if relevant, then run the
    timeout at regular interval (marching ants speed).
    
    (cherry picked from commit 668c9de5a556a1d5407ddca8b787b4fad4ea0faf)

 app/display/gimpdisplayshell-selection.c | 65 ++++++++++++++++----------------
 1 file changed, 33 insertions(+), 32 deletions(-)
---
diff --git a/app/display/gimpdisplayshell-selection.c b/app/display/gimpdisplayshell-selection.c
index 38756591e3..eca6cc1039 100644
--- a/app/display/gimpdisplayshell-selection.c
+++ b/app/display/gimpdisplayshell-selection.c
@@ -76,7 +76,7 @@ static void      selection_zoom_segs      (Selection          *selection,
 static void      selection_generate_segs  (Selection          *selection);
 static void      selection_free_segs      (Selection          *selection);
 
-static gboolean  selection_start_timeout  (Selection          *selection);
+static gboolean  selection_timeout        (Selection          *selection);
 
 static gboolean  selection_window_state_event      (GtkWidget           *shell,
                                                     GdkEventWindowState *event,
@@ -229,10 +229,22 @@ selection_start (Selection *selection)
   selection_stop (selection);
 
   /*  If this selection is paused, do not start it  */
-  if (selection->paused == 0 && selection->timeout == 0)
+  if (selection->paused == 0                             &&
+      gimp_display_get_image (selection->shell->display) &&
+      selection->show_selection)
     {
-      selection->timeout = g_idle_add ((GSourceFunc) selection_start_timeout,
-                                       selection);
+      /*  Draw the ants once  */
+      selection_timeout (selection);
+
+      if (selection->segs_in && selection->shell_visible)
+        {
+          GimpDisplayConfig *config = selection->shell->display->config;
+
+          selection->timeout = g_timeout_add_full (G_PRIORITY_DEFAULT_IDLE,
+                                                   config->marching_ants_speed,
+                                                   (GSourceFunc) selection_timeout,
+                                                   selection, NULL);
+        }
     }
 }
 
@@ -439,41 +451,30 @@ selection_free_segs (Selection *selection)
 }
 
 static gboolean
-selection_start_timeout (Selection *selection)
+selection_timeout (Selection *selection)
 {
-  /*  Draw the ants  */
-  if (gimp_display_get_image (selection->shell->display) &&
-      selection->show_selection)
-    {
-      GimpDisplayConfig *config = selection->shell->display->config;
-      gint64             time = g_get_monotonic_time ();
+  GimpDisplayConfig *config = selection->shell->display->config;
+  gint64             time   = g_get_monotonic_time ();
 
-      if ((time - selection->shell->selection_update) / 1000 > config->marching_ants_speed)
-        {
-          GdkWindow             *window;
-          cairo_rectangle_int_t  rect;
-          cairo_region_t        *region;
+  if ((time - selection->shell->selection_update) / 1000 > config->marching_ants_speed)
+    {
+      GdkWindow             *window;
+      cairo_rectangle_int_t  rect;
+      cairo_region_t        *region;
 
-          window = gtk_widget_get_window (GTK_WIDGET (selection->shell));
+      window = gtk_widget_get_window (GTK_WIDGET (selection->shell));
 
-          rect.x      = 0;
-          rect.y      = 0;
-          rect.width  = gdk_window_get_width  (window);
-          rect.height = gdk_window_get_height (window);
+      rect.x      = 0;
+      rect.y      = 0;
+      rect.width  = gdk_window_get_width  (window);
+      rect.height = gdk_window_get_height (window);
 
-          region = cairo_region_create_rectangle (&rect);
-          gtk_widget_queue_draw_region (GTK_WIDGET (selection->shell), region);
-          cairo_region_destroy (region);
-        }
-      else
-        {
-          return G_SOURCE_CONTINUE;
-        }
+      region = cairo_region_create_rectangle (&rect);
+      gtk_widget_queue_draw_region (GTK_WIDGET (selection->shell), region);
+      cairo_region_destroy (region);
     }
 
-  selection->timeout = 0;
-
-  return G_SOURCE_REMOVE;
+  return G_SOURCE_CONTINUE;
 }
 
 static void