[gtksourceview] gutter: ensure prelit calculation is included

[Christian Hergert <chergert src gnome org>]

commit 86b46d63a250a0d27fd04bc6723cbfdcad665ff9
Author: Christian Hergert <chergert redhat com>
Date:   Wed Apr 27 17:35:52 2022 -0700

    gutter: ensure prelit calculation is included

 gtksourceview/gtksourcegutter.c | 69 ++++++++++++++++++++++++++++++++++++-----
 1 file changed, 62 insertions(+), 7 deletions(-)
---
diff --git a/gtksourceview/gtksourcegutter.c b/gtksourceview/gtksourcegutter.c
index 4cfc96f2..add9c387 100644
--- a/gtksourceview/gtksourcegutter.c
+++ b/gtksourceview/gtksourcegutter.c
@@ -80,7 +80,11 @@ struct _GtkSourceGutter
        GtkTextWindowType     window_type;
        GtkOrientation        orientation;
 
+       double                pointer_x;
+       double                pointer_y;
+
        guint                 is_drawing : 1;
+       guint                 pointer_in_gutter : 1;
 };
 
 G_DEFINE_TYPE (GtkSourceGutter, gtk_source_gutter, GTK_TYPE_WIDGET)
@@ -320,10 +324,40 @@ gtk_source_gutter_measure (GtkWidget      *widget,
 }
 
 static void
-gtk_source_gutter_set_property (GObject       *object,
-                                guint          prop_id,
-                                const GValue  *value,
-                                GParamSpec    *pspec)
+gtk_source_gutter_motion_cb (GtkSourceGutter          *gutter,
+                            double                    x,
+                            double                    y,
+                            GtkEventControllerMotion *motion)
+{
+       g_assert (GTK_SOURCE_IS_GUTTER (gutter));
+       g_assert (GTK_IS_EVENT_CONTROLLER_MOTION (motion));
+
+       gutter->pointer_x = x;
+       gutter->pointer_y = y;
+       gutter->pointer_in_gutter = TRUE;
+
+       _gtk_source_gutter_queue_draw (gutter);
+}
+
+static void
+gtk_source_gutter_leave_cb (GtkSourceGutter          *gutter,
+                           GtkEventControllerMotion *motion)
+{
+       g_assert (GTK_SOURCE_IS_GUTTER (gutter));
+       g_assert (GTK_IS_EVENT_CONTROLLER_MOTION (motion));
+
+       gutter->pointer_x = -1;
+       gutter->pointer_y = -1;
+       gutter->pointer_in_gutter = FALSE;
+
+       _gtk_source_gutter_queue_draw (gutter);
+}
+
+static void
+gtk_source_gutter_set_property (GObject      *object,
+                                guint         prop_id,
+                                const GValue *value,
+                                GParamSpec   *pspec)
 {
        GtkSourceGutter *gutter = GTK_SOURCE_GUTTER (object);
 
@@ -457,15 +491,15 @@ gtk_source_gutter_init (GtkSourceGutter *gutter)
        motion = gtk_event_controller_motion_new ();
        g_signal_connect_swapped (motion,
                                  "enter",
-                                 G_CALLBACK (gtk_widget_queue_draw),
+                                 G_CALLBACK (gtk_source_gutter_motion_cb),
                                  gutter);
        g_signal_connect_swapped (motion,
                                  "leave",
-                                 G_CALLBACK (gtk_widget_queue_draw),
+                                 G_CALLBACK (gtk_source_gutter_leave_cb),
                                  gutter);
        g_signal_connect_swapped (motion,
                                  "motion",
-                                 G_CALLBACK (gtk_widget_queue_draw),
+                                 G_CALLBACK (gtk_source_gutter_motion_cb),
                                  gutter);
        gtk_widget_add_controller (GTK_WIDGET (gutter), motion);
 }
@@ -742,6 +776,27 @@ gtk_source_gutter_snapshot (GtkWidget   *widget,
                                                      needs_wrap_first,
                                                      needs_wrap_last);
 
+       /* Get the line under the pointer so we can set "prelit" on it */
+       if (gutter->pointer_in_gutter)
+       {
+               GtkTextIter pointer;
+               GdkRectangle pointer_rect;
+
+               gtk_text_view_get_iter_at_location (text_view,
+                                                   &pointer,
+                                                   0,
+                                                   visible_rect.y + gutter->pointer_y);
+               gtk_text_view_get_iter_location (text_view, &pointer, &pointer_rect);
+               pointer_rect.y -= visible_rect.y;
+
+               if (gutter->pointer_y >= pointer_rect.y &&
+                   gutter->pointer_y <= pointer_rect.y + pointer_rect.height)
+               {
+                       guint line = gtk_text_iter_get_line (&pointer);
+                       gtk_source_gutter_lines_add_class (gutter->lines, line, "prelit");
+               }
+       }
+
        /* Draw the current-line highlight if necessary */
        if (gtk_source_view_get_highlight_current_line (gutter->view) &&
            !gtk_text_buffer_get_selection_bounds (buffer, &cur, &sel))