gui/fading-label: Rewrite using PangoLayout directly

Instead of an internal label widget, store the text and the PangoLayout
directly, and only render them. Cache as much as possible to avoid
font reshaping.

Part-of: <https://gitlab.gnome.org/GNOME/gnome-calendar/-/merge_requests/765>

src/gui/gcal-event-widget.blp

@@ -54,7 +54,7 @@ template $GcalEventWidget: Widget {
       }
 
       Inscription {
-        text: bind summary_label.label;
+        text: bind summary_label.text;
         hexpand: true;
         vexpand: true;
         xalign: 0.0;
@@ -68,13 +68,13 @@ template $GcalEventWidget: Widget {
       spacing: 4;
 
       $GcalFadingLabel summary_label {
-        label: bind template.event as <$GcalEvent>.summary;
+        text: bind template.event as <$GcalEvent>.summary;
+        hexpand: true;
+        vexpand: true;
       }
 
       Label timestamp_label {
         halign: end;
-        hexpand: true;
-        vexpand: true;
 
         styles [
           "dimmed",

src/gui/gcal-fading-label.c

@@ -8,6 +8,8 @@
 
 /* Copied from libadwaita 1.8 and adapted for use in gnome-calendar. */
 
+#define G_LOG_DOMAIN "GcalFadingLabel"
+
 #include "config.h"
 #include "gcal-fading-label.h"
 
@@ -20,7 +22,16 @@ struct _GcalFadingLabel
 {
   GtkWidget parent_instance;
 
-  GtkWidget *label;
+  PangoLayout *layout;
+
+  GskRenderNode *cached_text_node;
+  PangoRectangle cached_extents;
+  gboolean cached_extents_valid;
+  int cached_ascent;
+  int cached_descent;
+
+  char *text;
+
   gfloat align;
 };
 
@@ -28,7 +39,7 @@ G_DEFINE_FINAL_TYPE (GcalFadingLabel, gcal_fading_label, GTK_TYPE_WIDGET)
 
 enum {
   PROP_0,
-  PROP_LABEL,
+  PROP_TEXT,
   PROP_ALIGN,
   LAST_PROP
 };
@@ -39,10 +50,9 @@ static gboolean
 is_rtl (GcalFadingLabel *self)
 {
   PangoDirection pango_direction = PANGO_DIRECTION_NEUTRAL;
-  const gchar *label = gcal_fading_label_get_label (self);
 
-  if (label)
+  if (self->text)
-    pango_direction = gcal_find_base_dir (label, -1);
+    pango_direction = gcal_find_base_dir (self->text, -1);
 
   if (pango_direction == PANGO_DIRECTION_RTL)
     return TRUE;
@@ -53,6 +63,46 @@ is_rtl (GcalFadingLabel *self)
   return gtk_widget_get_direction (GTK_WIDGET (self)) == GTK_TEXT_DIR_RTL;
 }
 
+static int
+get_line_pixels (GcalFadingLabel *self,
+                 int            *baseline)
+{
+  if (self->cached_ascent == -1 || self->cached_descent == -1)
+    {
+      PangoFontMetrics *metrics;
+      PangoContext *context;
+
+      context = gtk_widget_get_pango_context (GTK_WIDGET (self));
+      metrics = pango_context_get_metrics (context, NULL, NULL);
+
+      self->cached_ascent = pango_font_metrics_get_ascent (metrics);
+      self->cached_descent = pango_font_metrics_get_descent (metrics);
+
+      g_clear_pointer (&metrics, pango_font_metrics_unref);
+    }
+
+  if (baseline)
+    *baseline = self->cached_ascent;
+
+  return self->cached_ascent + self->cached_descent;
+}
+
+static void
+gcal_fading_label_css_changed (GtkWidget         *widget,
+                               GtkCssStyleChange *change)
+{
+  GcalFadingLabel *self = GCAL_FADING_LABEL (widget);
+
+  GTK_WIDGET_CLASS (gcal_fading_label_parent_class)->css_changed (widget, change);
+
+  self->cached_ascent = -1;
+  self->cached_descent = -1;
+  self->cached_extents_valid = FALSE;
+  g_clear_pointer (&self->cached_text_node, gsk_render_node_unref);
+
+  gtk_widget_queue_draw (widget);
+}
+
 static void
 gcal_fading_label_measure (GtkWidget      *widget,
                           GtkOrientation  orientation,
@@ -64,39 +114,34 @@ gcal_fading_label_measure (GtkWidget      *widget,
 {
   GcalFadingLabel *self = GCAL_FADING_LABEL (widget);
 
-  gtk_widget_measure (self->label,
+  switch (orientation)
-                      orientation,
+    {
-                      for_size,
+    case GTK_ORIENTATION_VERTICAL:
-                      min, nat,
+      {
-                      min_baseline, nat_baseline);
+        int line_pixels, baseline;
 
-  if (orientation == GTK_ORIENTATION_HORIZONTAL && min)
+        line_pixels = get_line_pixels (self, &baseline);
-    *min = 0;
-}
 
-static void
+        *min = line_pixels;
-gcal_fading_label_size_allocate (GtkWidget *widget,
+        *nat = line_pixels;
-                                gint        width,
+      }
-                                gint        height,
+      break;
-                                gint        baseline)
-{
-  GcalFadingLabel *self = GCAL_FADING_LABEL (widget);
-  GskTransform *transform;
-  gfloat align = is_rtl (self) ? 1 - self->align : self->align;
-  gint child_width;
-  gfloat offset;
 
-  gtk_widget_measure (self->label,
+    case GTK_ORIENTATION_HORIZONTAL:
-                      GTK_ORIENTATION_HORIZONTAL,
+      *min = 0;
-                      height,
+      *nat = 0;
-                      NULL,
+      break;
-                      &child_width,
-                      NULL, NULL);
 
-  offset = (width - child_width) * align;
+    default:
-  transform = gsk_transform_translate (NULL, &GRAPHENE_POINT_INIT (offset, 0));
+      g_assert_not_reached ();
+    }
 
-  gtk_widget_allocate (self->label, child_width, height, baseline, transform);
+  *min = PANGO_PIXELS_CEIL (*min);
+  *nat = PANGO_PIXELS_CEIL (*nat);
+  if (*min_baseline > 0)
+    *min_baseline = PANGO_PIXELS_CEIL (*min_baseline);
+  if (*nat_baseline > 0)
+    *nat_baseline = PANGO_PIXELS_CEIL (*nat_baseline);
 }
 
 static void
@@ -104,41 +149,49 @@ gcal_fading_label_snapshot (GtkWidget   *widget,
                             GtkSnapshot *snapshot)
 {
   GcalFadingLabel *self = GCAL_FADING_LABEL (widget);
-  g_autoptr (GskRenderNode) node = NULL;
+  float align;
-  g_autoptr (GtkSnapshot) child_snapshot = NULL;
+  int height;
-  graphene_rect_t bounds;
+  int width;
-  gfloat align = is_rtl (self) ? 1 - self->align : self->align;
+
-  gint width = gtk_widget_get_width (widget);
+  width = gtk_widget_get_width (widget);
-  gint clipped_size;
+  height = gtk_widget_get_height (widget);
 
   if (width <= 0)
     return;
 
-  clipped_size = gtk_widget_get_width (self->label) - width;
+  if (!self->cached_extents_valid)
-
-  if (clipped_size <= 0)
     {
-      gtk_widget_snapshot_child (widget, self->label, snapshot);
+      pango_layout_get_pixel_extents (self->layout, NULL, &self->cached_extents);
+      self->cached_extents_valid = TRUE;
+    }
+
+  if (!self->cached_text_node)
+    {
+      g_autoptr (GtkSnapshot) text_snapshot = NULL;
+      GdkRGBA foreground_color;
+
+      gtk_widget_get_color (widget, &foreground_color);
+
+      text_snapshot = gtk_snapshot_new ();
+      gtk_snapshot_append_layout (text_snapshot, self->layout, &foreground_color);
+
+      self->cached_text_node = gtk_snapshot_free_to_node (g_steal_pointer (&text_snapshot));
+    }
+
+  if (self->cached_extents.x + self->cached_extents.width <= width)
+    {
+      gtk_snapshot_append_node (snapshot, self->cached_text_node);
       return;
     }
 
-  child_snapshot = gtk_snapshot_new ();
+  align = is_rtl (self) ? 1 - self->align : self->align;
-  gtk_widget_snapshot_child (widget, self->label, child_snapshot);
-  node = gtk_snapshot_free_to_node (g_steal_pointer (&child_snapshot));
-
-  gsk_render_node_get_bounds (node, &bounds);
-  bounds.origin.x = 0;
-  bounds.origin.y = floor (bounds.origin.y);
-  bounds.size.width = width;
-  bounds.size.height = ceil (bounds.size.height) + 1;
 
   gtk_snapshot_push_mask (snapshot, GSK_MASK_MODE_INVERTED_ALPHA);
 
   if (align > 0)
     {
       gtk_snapshot_append_linear_gradient (snapshot,
-                                           &GRAPHENE_RECT_INIT (0, bounds.origin.y,
+                                           &GRAPHENE_RECT_INIT (0, 0, FADE_WIDTH, height),
-                                                                FADE_WIDTH, bounds.size.height),
                                            &GRAPHENE_POINT_INIT (0, 0),
                                            &GRAPHENE_POINT_INIT (FADE_WIDTH, 0),
                                            (GskColorStop[2]) {
@@ -151,8 +204,7 @@ gcal_fading_label_snapshot (GtkWidget   *widget,
   if (align < 1)
     {
       gtk_snapshot_append_linear_gradient (snapshot,
-                                           &GRAPHENE_RECT_INIT (width - FADE_WIDTH, bounds.origin.y,
+                                           &GRAPHENE_RECT_INIT (width - FADE_WIDTH, 0, FADE_WIDTH, height),
-                                                                FADE_WIDTH, bounds.size.height),
                                            &GRAPHENE_POINT_INIT (width, 0),
                                            &GRAPHENE_POINT_INIT (width - FADE_WIDTH, 0),
                                            (GskColorStop[2]) {
@@ -164,8 +216,8 @@ gcal_fading_label_snapshot (GtkWidget   *widget,
 
   gtk_snapshot_pop (snapshot);
 
-  gtk_snapshot_push_clip (snapshot, &bounds);
+  gtk_snapshot_push_clip (snapshot, &GRAPHENE_RECT_INIT (0, 0, width, height));
-  gtk_snapshot_append_node (snapshot, node);
+  gtk_snapshot_append_node (snapshot, self->cached_text_node);
   gtk_snapshot_pop (snapshot);
 
   gtk_snapshot_pop (snapshot);
@@ -180,8 +232,8 @@ gcal_fading_label_get_property (GObject    *object,
   GcalFadingLabel *self = GCAL_FADING_LABEL (object);
 
   switch (prop_id) {
-  case PROP_LABEL:
+  case PROP_TEXT:
-    g_value_set_string (value, gcal_fading_label_get_label (self));
+    g_value_set_string (value, self->text);
     break;
 
   case PROP_ALIGN:
@@ -202,8 +254,8 @@ gcal_fading_label_set_property (GObject      *object,
   GcalFadingLabel *self = GCAL_FADING_LABEL (object);
 
   switch (prop_id) {
-  case PROP_LABEL:
+  case PROP_TEXT:
-    gcal_fading_label_set_label (self, g_value_get_string (value));
+    gcal_fading_label_set_text (self, g_value_get_string (value));
     break;
 
   case PROP_ALIGN:
@@ -220,7 +272,8 @@ gcal_fading_label_dispose (GObject *object)
 {
   GcalFadingLabel *self = GCAL_FADING_LABEL (object);
 
-  g_clear_pointer (&self->label, gtk_widget_unparent);
+  g_clear_object (&self->layout);
+  g_clear_pointer (&self->cached_text_node, gsk_render_node_unref);
 
   G_OBJECT_CLASS (gcal_fading_label_parent_class)->dispose (object);
 }
@@ -235,12 +288,12 @@ gcal_fading_label_class_init (GcalFadingLabelClass *klass)
   object_class->set_property = gcal_fading_label_set_property;
   object_class->dispose = gcal_fading_label_dispose;
 
+  widget_class->css_changed = gcal_fading_label_css_changed;
   widget_class->measure = gcal_fading_label_measure;
-  widget_class->size_allocate = gcal_fading_label_size_allocate;
   widget_class->snapshot = gcal_fading_label_snapshot;
 
-  props[PROP_LABEL] =
+  props[PROP_TEXT] =
-    g_param_spec_string ("label", NULL, NULL,
+    g_param_spec_string ("text", NULL, NULL,
                          NULL,
                          G_PARAM_READWRITE | G_PARAM_STATIC_STRINGS | G_PARAM_EXPLICIT_NOTIFY);
 
@@ -255,32 +308,41 @@ gcal_fading_label_class_init (GcalFadingLabelClass *klass)
 static void
 gcal_fading_label_init (GcalFadingLabel *self)
 {
-  self->label = gtk_label_new (NULL);
+  self->layout = gtk_widget_create_pango_layout (GTK_WIDGET (self), NULL);
-  gtk_label_set_single_line_mode (GTK_LABEL (self->label), TRUE);
+  self->cached_ascent = -1;
-
+  self->cached_descent = -1;
-  gtk_widget_set_parent (self->label, GTK_WIDGET (self));
+  self->cached_extents_valid = FALSE;
 }
 
 const gchar *
-gcal_fading_label_get_label (GcalFadingLabel *self)
+gcal_fading_label_get_text (GcalFadingLabel *self)
 {
   g_return_val_if_fail (GCAL_IS_FADING_LABEL (self), NULL);
 
-  return gtk_label_get_label (GTK_LABEL (self->label));
+  return self->text;
 }
 
 void
-gcal_fading_label_set_label (GcalFadingLabel *self,
+gcal_fading_label_set_text (GcalFadingLabel *self,
-                             const gchar      *label)
+                            const gchar     *text)
 {
   g_return_if_fail (GCAL_IS_FADING_LABEL (self));
 
-  if (!g_strcmp0 (label, gcal_fading_label_get_label (self)))
+  if (!g_set_str (&self->text, text))
     return;
 
-  gtk_label_set_label (GTK_LABEL (self->label), label);
+  pango_layout_set_text (self->layout,
+                         self->text ? self->text : "",
+                         -1);
 
-  g_object_notify_by_pspec (G_OBJECT (self), props[PROP_LABEL]);
+  self->cached_ascent = -1;
+  self->cached_descent = -1;
+  self->cached_extents_valid = FALSE;
+  g_clear_pointer (&self->cached_text_node, gsk_render_node_unref);
+
+  gtk_widget_queue_draw (GTK_WIDGET (self));
+
+  g_object_notify_by_pspec (G_OBJECT (self), props[PROP_TEXT]);
 }
 
 float
@@ -304,7 +366,7 @@ gcal_fading_label_set_align (GcalFadingLabel *self,
 
   self->align = align;
 
-  gtk_widget_queue_allocate (GTK_WIDGET (self));
+  gtk_widget_queue_draw (GTK_WIDGET (self));
 
   g_object_notify_by_pspec (G_OBJECT (self), props[PROP_ALIGN]);
 }

src/gui/gcal-fading-label.h

@@ -18,8 +18,8 @@ G_BEGIN_DECLS
 
 G_DECLARE_FINAL_TYPE (GcalFadingLabel, gcal_fading_label, GCAL, FADING_LABEL, GtkWidget)
 
-const gchar *gcal_fading_label_get_label (GcalFadingLabel *self);
+const gchar *gcal_fading_label_get_text  (GcalFadingLabel *self);
-void         gcal_fading_label_set_label (GcalFadingLabel *self,
+void         gcal_fading_label_set_text  (GcalFadingLabel *self,
                                           const gchar     *label);
 gfloat       gcal_fading_label_get_align (GcalFadingLabel *self);
 void         gcal_fading_label_set_align (GcalFadingLabel *self,