[pango/line-height-attribute: 28/30] layout: Handle line-height attributes

[Matthias Clasen <matthiasc src gnome org>]

commit 5a20c4837a6d08ca2d4be46e33255fcd9d8fd575
Author: Matthias Clasen <mclasen redhat com>
Date:   Sat Aug 7 10:39:32 2021 -0400

    layout: Handle line-height attributes
    
    Modify the height and vertical origin of logical
    extents according to the line height attributes.
    
    We currently apply half the leading above and
    half below the content (i.e., lines are vertically
    centered in their modified height).

 pango/pango-layout.c | 31 ++++++++++++++++++++++++++++++-
 1 file changed, 30 insertions(+), 1 deletion(-)
---
diff --git a/pango/pango-layout.c b/pango/pango-layout.c
index 20208dec..447bf890 100644
--- a/pango/pango-layout.c
+++ b/pango/pango-layout.c
@@ -78,6 +78,7 @@
 #include "pango-impl-utils.h"
 #include "pango-glyph-item.h"
 #include <string.h>
+#include <math.h>
 
 #include "pango-layout-private.h"
 #include "pango-attributes-private.h"
@@ -107,6 +108,8 @@ struct _ItemProperties
   gboolean        shape_set;
   PangoRectangle *shape_ink_rect;
   PangoRectangle *shape_logical_rect;
+  double line_height;
+  int    absolute_line_height;
 };
 
 typedef struct _PangoLayoutLinePrivate PangoLayoutLinePrivate;
@@ -587,9 +590,12 @@ pango_layout_get_indent (PangoLayout *layout)
  * The default value is 0.
  *
  * Note: Since 1.44, Pango is using the line height (as determined
- * by the font) for placing lines when the line height factor is set
+ * by the font) for placing lines when the line spacing factor is set
  * to a non-zero value with [method@Pango.Layout.set_line_spacing].
  * In that case, the @spacing set with this function is ignored.
+ *
+ * Note: for semantics that are closer to the CSS line-height
+ * property, see [func@Pango.attr_line_height_new].
  */
 void
 pango_layout_set_spacing (PangoLayout *layout,
@@ -4152,6 +4158,8 @@ affects_itemization (PangoAttribute *attr,
     case PANGO_ATTR_LETTER_SPACING:
     case PANGO_ATTR_SHAPE:
     case PANGO_ATTR_RISE:
+    case PANGO_ATTR_LINE_HEIGHT:
+    case PANGO_ATTR_ABSOLUTE_LINE_HEIGHT:
       return TRUE;
     default:
       return FALSE;
@@ -5107,9 +5115,20 @@ pango_layout_run_get_extents_and_height (PangoLayoutRun *run,
       if (!metrics)
         metrics = pango_font_get_metrics (run->item->analysis.font,
                                           run->item->analysis.language);
+
       *height = pango_font_metrics_get_height (metrics);
     }
 
+  if (properties.absolute_line_height != 0 || properties.line_height != 0.0)
+    {
+      int line_height, leading;
+
+      line_height = MAX (properties.absolute_line_height, ceilf (properties.line_height * 
run_logical->height));
+      leading = line_height - run_logical->height;
+      run_logical->y -= leading / 2;
+      run_logical->height += leading;
+    }
+
   if (run->item->analysis.flags & PANGO_ANALYSIS_FLAG_CENTERED_BASELINE)
     {
       gboolean is_hinted = (run_logical->y & run_logical->height & (PANGO_SCALE - 1)) == 0;
@@ -5988,6 +6007,8 @@ pango_layout_get_item_properties (PangoItem      *item,
   properties->shape_set = FALSE;
   properties->shape_ink_rect = NULL;
   properties->shape_logical_rect = NULL;
+  properties->line_height = 0.0;
+  properties->absolute_line_height = 0;
 
   while (tmp_list)
     {
@@ -6051,6 +6072,14 @@ pango_layout_get_item_properties (PangoItem      *item,
           properties->shape_ink_rect = &((PangoAttrShape *)attr)->ink_rect;
           break;
 
+        case PANGO_ATTR_LINE_HEIGHT:
+          properties->line_height = ((PangoAttrFloat *)attr)->value;
+          break;
+
+        case PANGO_ATTR_ABSOLUTE_LINE_HEIGHT:
+          properties->absolute_line_height = ((PangoAttrInt *)attr)->value;
+          break;
+
         default:
           break;
         }