[gtk/gbsneto/inscription-justify] inscription: Derive row alignment from xalign

[Georges Basile Stavracas Neto <gbsneto src gnome org>]

commit 6a3891a9652635ec822a2d4b7bf63c3791e30807
Author: Georges Basile Stavracas Neto <georges stavracas gmail com>
Date:   Sun Jun 12 14:27:33 2022 -0300

    inscription: Derive row alignment from xalign
    
    Texts usually want the alignment of each row to match the xalign of
    the text itself.
    
    Derive the alignment of the PangoLayout from the xalign property of
    the inscription. Because Pango doesn't provide float row alignment,
    linearly map that from the xalign.

 gtk/gtkinscription.c | 35 +++++++++++++++++++++++++++++++++++
 1 file changed, 35 insertions(+)
---
diff --git a/gtk/gtkinscription.c b/gtk/gtkinscription.c
index c8937df9e9..04a5128f3d 100644
--- a/gtk/gtkinscription.c
+++ b/gtk/gtkinscription.c
@@ -233,6 +233,27 @@ gtk_inscription_set_property (GObject      *object,
     }
 }
 
+static void
+update_pango_alignment (GtkInscription *self)
+{
+  PangoAlignment align;
+  gboolean ltr;
+
+  g_assert (self->layout != NULL);
+  g_assert (self->xalign >= 0.0 && self->xalign <= 1.0);
+
+  ltr = _gtk_widget_get_direction (GTK_WIDGET (self)) != GTK_TEXT_DIR_RTL;
+
+  if (self->xalign < 0.33)
+      align = ltr ? PANGO_ALIGN_LEFT : PANGO_ALIGN_RIGHT;
+  else if (self->xalign < 0.67)
+      align = PANGO_ALIGN_CENTER;
+  else
+      align = ltr ? PANGO_ALIGN_RIGHT : PANGO_ALIGN_LEFT;
+
+  pango_layout_set_alignment (self->layout, align);
+}
+
 static void
 gtk_inscription_update_layout_attributes (GtkInscription *self,
                                           PangoAttrList  *css_attrs)
@@ -267,6 +288,17 @@ gtk_inscription_css_changed (GtkWidget         *widget,
     }
 }
 
+static void
+gtk_inscription_direction_changed (GtkWidget        *widget,
+                                   GtkTextDirection  previous_direction)
+{
+  GtkInscription *self = GTK_INSCRIPTION (widget);
+
+  GTK_WIDGET_CLASS (gtk_inscription_parent_class)->direction_changed (widget, previous_direction);
+
+  update_pango_alignment (self);
+}
+
 static PangoFontMetrics *
 gtk_inscription_get_font_metrics (GtkInscription *self)
 {
@@ -491,6 +523,7 @@ gtk_inscription_class_init (GtkInscriptionClass *klass)
   gobject_class->set_property = gtk_inscription_set_property;
 
   widget_class->css_changed = gtk_inscription_css_changed;
+  widget_class->direction_changed = gtk_inscription_direction_changed;
   widget_class->measure = gtk_inscription_measure;
   widget_class->size_allocate = gtk_inscription_allocate;
   widget_class->snapshot = gtk_inscription_snapshot;
@@ -988,6 +1021,8 @@ gtk_inscription_set_xalign (GtkInscription *self,
 
   self->xalign = xalign;
 
+  update_pango_alignment (self);
+
   gtk_widget_queue_draw (GTK_WIDGET (self));
 
   g_object_notify_by_pspec (G_OBJECT (self), properties[PROP_XALIGN]);