[pango/empty-line-height-attr-fix: 1/5] pangocairo: Round font metrics when appropriate

[Matthias Clasen <matthiasc src gnome org>]

commit f178bb42d3622b3144bc30d5c5d99c884eee0455
Author: Matthias Clasen <mclasen redhat com>
Date:   Thu Sep 30 17:08:29 2021 -0400

    pangocairo: Round font metrics when appropriate
    
    When metrics hinting is on, we used to provide rounded
    font metrics. We should keep doing that since otherwise
    we end up with logical rects sometimes being rounded
    and sometimes not, leading to jumping empty lines.
    
    Test included.
    
    Fixes: #421

 pango/pangocairo-fcfont.c | 14 +++++++++++++-
 tests/testmisc.c          | 41 +++++++++++++++++++++++++++++++++++++++++
 2 files changed, 54 insertions(+), 1 deletion(-)
---
diff --git a/pango/pangocairo-fcfont.c b/pango/pangocairo-fcfont.c
index 0019f83a..85cc45c8 100644
--- a/pango/pangocairo-fcfont.c
+++ b/pango/pangocairo-fcfont.c
@@ -76,8 +76,20 @@ pango_cairo_fc_font_create_base_metrics_for_context (PangoCairoFont *cfont,
                                                     PangoContext   *context)
 {
   PangoFcFont *fcfont = (PangoFcFont *) (cfont);
+  PangoFontMetrics *metrics;
+  const cairo_font_options_t *options;
 
-  return pango_fc_font_create_base_metrics_for_context (fcfont, context);
+  metrics = pango_fc_font_create_base_metrics_for_context (fcfont, context);
+
+  options = pango_cairo_context_get_font_options (context);
+  if (cairo_font_options_get_hint_metrics (options) == CAIRO_HINT_METRICS_ON)
+    {
+      metrics->ascent = PANGO_PIXELS_CEIL (metrics->ascent) * PANGO_SCALE;
+      metrics->descent = PANGO_PIXELS_CEIL (metrics->descent) * PANGO_SCALE;
+      metrics->height = PANGO_PIXELS_CEIL (metrics->height) * PANGO_SCALE;
+    }
+
+  return metrics;
 }
 
 static void
diff --git a/tests/testmisc.c b/tests/testmisc.c
index 60694134..cf64e00f 100644
--- a/tests/testmisc.c
+++ b/tests/testmisc.c
@@ -489,6 +489,46 @@ test_extents (void)
   g_object_unref (context);
 }
 
+static void
+test_empty_line_height (void)
+{
+  PangoContext *context;
+  PangoLayout *layout;
+  PangoRectangle ext1, ext2, ext3;
+  cairo_font_options_t *options;
+  int hint;
+
+  context = pango_font_map_create_context (pango_cairo_font_map_get_default ());
+
+  for (hint = CAIRO_HINT_METRICS_OFF; hint <= CAIRO_HINT_METRICS_ON; hint++)
+    {
+      options = cairo_font_options_create ();
+      cairo_font_options_set_hint_metrics (options, hint);
+      pango_cairo_context_set_font_options (context, options);
+      cairo_font_options_destroy (options);
+
+      layout = pango_layout_new (context);
+
+      pango_layout_get_extents (layout, NULL, &ext1);
+
+      pango_layout_set_text (layout, "a", 1);
+
+      pango_layout_get_extents (layout, NULL, &ext2);
+
+      g_assert_cmpint (ext1.height, ==, ext2.height);
+
+      pango_layout_set_text (layout, "Pg", 1);
+
+      pango_layout_get_extents (layout, NULL, &ext3);
+
+      g_assert_cmpint (ext2.height, ==, ext3.height);
+
+      g_object_unref (layout);
+    }
+
+  g_object_unref (context);
+}
+
 int
 main (int argc, char *argv[])
 {
@@ -514,6 +554,7 @@ main (int argc, char *argv[])
   g_test_add_func ("/bidi/get-cursor", test_get_cursor);
   g_test_add_func ("/layout/index-to-x", test_index_to_x);
   g_test_add_func ("/layout/extents", test_extents);
+  g_test_add_func ("/layout/empty-line-height", test_empty_line_height);
 
   return g_test_run ();
 }