Add line-height attributes

Add attributes for line-height, in a relative and
absolute variant.

This will be used to grow the logical extents of
runs in a way that is compatible with CSS semantics.

In markup, we support a new line_height attribute
that will be interpreted as absolute if it is an
integer > 1024, and as a relative factor otherwise.

5 files changed, 108 insertions, 0 deletions

diff --git a/docs/pango_markup.md b/docs/pango_markup.md
index 16359777..03718907 100644
--- a/docs/pango_markup.md
+++ b/docs/pango_markup.md
@@ -190,6 +190,12 @@ allow_breaks
 : 'true' or 'false' to indicate whether breaking lines is allowed. Available
   since Pango 1.44.
 
+line_height
+: Overrides the line height. The value can be either a factor (< 1024) that is
+  used to scale up the logical extents of runs or an absolute value (in 1024th
+  of a point).
+  Available since Pango 1.50.
+
 ## Convenience Tags
 
 `<b>`
diff --git a/pango/pango-attributes.c b/pango/pango-attributes.c
index 1a4a9443..fdb37f56 100644
--- a/pango/pango-attributes.c
+++ b/pango/pango-attributes.c
@@ -1341,6 +1341,58 @@ pango_attr_overline_color_new (guint16 red,
   return pango_attr_color_new (&klass, red, green, blue);
 }
 
+/**
+ * pango_attr_line_height_new:
+ * @factor: the scaling factor to apply to the logical height
+ *
+ * Modify the height of logical line extents by a factor.
+ *
+ * This affects the values returned by
+ * [method@Pango.LayoutLine.get_extents],
+ * [method@Pango.LayoutLine.get_pixel_extents] and
+ * [method@Pango.LayoutIter.get_line_extents].
+ *
+ *
+ * Since: 1.50
+ */
+PangoAttribute *
+pango_attr_line_height_new (double factor)
+{
+  static const PangoAttrClass klass = {
+    PANGO_ATTR_LINE_HEIGHT,
+    pango_attr_float_copy,
+    pango_attr_float_destroy,
+    pango_attr_float_equal
+  };
+
+  return pango_attr_float_new (&klass, factor);
+}
+
+/**
+ * pango_attr_line_height_new_absolute:
+ * @height: the line height, in %PANGO_SCALE-ths of a point
+ *
+ * Override the height of logical line extents to be @height.
+ *
+ * This affects the values returned by
+ * [method@Pango.LayoutLine.get_extents],
+ * [method@Pango.LayoutLine.get_pixel_extents] and
+ * [method@Pango.LayoutIter.get_line_extents].
+ *
+ * Since: 1.50
+ */
+PangoAttribute *
+pango_attr_line_height_new_absolute (int height)
+{
+  static const PangoAttrClass klass = {
+    PANGO_ATTR_ABSOLUTE_LINE_HEIGHT,
+    pango_attr_int_copy,
+    pango_attr_int_destroy,
+    pango_attr_int_equal
+  };
+
+  return pango_attr_int_new (&klass, height);
+}
 /*
  * Attribute List
  */
@@ -2559,6 +2611,7 @@ pango_attribute_as_float (PangoAttribute *attr)
   switch (attr->klass->type)
     {
     case PANGO_ATTR_SCALE:
+    case PANGO_ATTR_LINE_HEIGHT:
       return (PangoAttrFloat *)attr;
 
     default:
diff --git a/pango/pango-attributes.h b/pango/pango-attributes.h
index 6f18718e..c28623fb 100644
--- a/pango/pango-attributes.h
+++ b/pango/pango-attributes.h
@@ -160,6 +160,7 @@ typedef struct _PangoAttrIterator PangoAttrIterator;
  * @PANGO_ATTR_INSERT_HYPHENS: whether to insert hyphens at intra-word line breaks ([struct@Pango.AttrInt]). Since 1.44
  * @PANGO_ATTR_OVERLINE: whether the text has an overline ([struct@Pango.AttrInt]). Since 1.46
  * @PANGO_ATTR_OVERLINE_COLOR: overline color ([struct@Pango.AttrColor]). Since 1.46
+ * @PANGO_ATTR_LINE_HEIGHT: line height factor ([struct@Pango.AttrFloat]). Since: 1.50
  *
  * The `PangoAttrType` distinguishes between different types of attributes.
  *
@@ -201,6 +202,8 @@ typedef enum
   PANGO_ATTR_INSERT_HYPHENS,	/* PangoAttrInt */
   PANGO_ATTR_OVERLINE,		/* PangoAttrInt */
   PANGO_ATTR_OVERLINE_COLOR,	/* PangoAttrColor */
+  PANGO_ATTR_LINE_HEIGHT,	/* PangoAttrFloat */
+  PANGO_ATTR_ABSOLUTE_LINE_HEIGHT, /* PangoAttrInt */
 } PangoAttrType;
 
 /**
@@ -611,6 +614,11 @@ typedef enum {
 PANGO_AVAILABLE_IN_1_44
 PangoAttribute *pango_attr_show_new              (PangoShowFlags flags);
 
+PANGO_AVAILABLE_IN_1_50
+PangoAttribute *pango_attr_line_height_new (double factor);
+PANGO_AVAILABLE_IN_1_50
+PangoAttribute *pango_attr_line_height_new_absolute (int height);
+
 PANGO_AVAILABLE_IN_ALL
 GType              pango_attr_list_get_type      (void) G_GNUC_CONST;
 PANGO_AVAILABLE_IN_ALL
diff --git a/pango/pango-layout.c b/pango/pango-layout.c
index e0475a5e..20208dec 100644
--- a/pango/pango-layout.c
+++ b/pango/pango-layout.c
@@ -638,6 +638,9 @@ pango_layout_get_spacing (PangoLayout *layout)
  *
  * If @factor is zero (the default), spacing is applied as before.
  *
+ * Note: for semantics that are closer to the CSS line-height
+ * property, see [func@Pango.attr_line_height_new].
+ *
  * Since: 1.44
  */
 void
diff --git a/pango/pango-markup.c b/pango/pango-markup.c
index 5394c772..00b16943 100644
--- a/pango/pango-markup.c
+++ b/pango/pango-markup.c
@@ -977,6 +977,29 @@ span_parse_int (const char *attr_name,
 }
 
 static gboolean
+span_parse_float (const char  *attr_name,
+                  const char  *attr_val,
+                  double      *val,
+                  int          line_number,
+                  GError     **error)
+{
+  *val = g_ascii_strtod (attr_val, NULL);
+  if (errno != 0)
+    {
+      g_set_error (error,
+                   G_MARKUP_ERROR,
+                   G_MARKUP_ERROR_INVALID_CONTENT,
+                   _("Value of '%s' attribute on <span> tag "
+                     "on line %d could not be parsed; "
+                     "should be a number, not '%s'"),
+                   attr_name, line_number, attr_val);
+      return FALSE;
+    }
+
+  return TRUE;
+}
+
+static gboolean
 span_parse_boolean (const char *attr_name,
 		    const char *attr_val,
 		    gboolean *val,
@@ -1200,6 +1223,7 @@ span_parse_func     (MarkupData            *md G_GNUC_UNUSED,
   const char *allow_breaks = NULL;
   const char *insert_hyphens = NULL;
   const char *show = NULL;
+  const char *line_height = NULL;
 
   g_markup_parse_context_get_position (context,
 				       &line_number, &char_number);
@@ -1278,6 +1302,7 @@ span_parse_func     (MarkupData            *md G_GNUC_UNUSED,
       case 'l':
 	CHECK_ATTRIBUTE (lang);
 	CHECK_ATTRIBUTE (letter_spacing);
+        CHECK_ATTRIBUTE (line_height);
 	break;
       case 'o':
 	CHECK_ATTRIBUTE (overline);
@@ -1639,6 +1664,19 @@ span_parse_func     (MarkupData            *md G_GNUC_UNUSED,
       add_attribute (tag, pango_attr_letter_spacing_new (n));
     }
 
+  if (G_UNLIKELY (line_height))
+    {
+      double f = 0;
+
+      if (!span_parse_float ("line_height", line_height, &f, line_number, error))
+        goto error;
+
+      if (f > 1024.0 && strchr (line_height, ".") == 0)
+        add_attribute (tag, pango_attr_line_height_new_absolute ((int)f));
+      else
+        add_attribute (tag, pango_attr_line_height_new (f));
+    }
+
   if (G_UNLIKELY (lang))
     {
       add_attribute (tag,