[pango/visible-things: 12/13] fc: Implement showing space

[Matthias Clasen <matthiasc src gnome org>]

commit ff7deea2263c1310c15a62bb4efdd782cbbf9b3e
Author: Matthias Clasen <mclasen redhat com>
Date:   Sun Jul 7 14:15:00 2019 -0400

    fc: Implement showing space
    
    When told to make space visible, we use the glyph
    for 0x2324 instead of 0x20. We have to do some
    post-processing to counteract harfbuzz using
    space glyphs for its own purposes.

 pango/pangofc-shape.c | 32 ++++++++++++++++++++++++++++++++
 1 file changed, 32 insertions(+)
---
diff --git a/pango/pangofc-shape.c b/pango/pangofc-shape.c
index 3e9502ff..ca2a819a 100644
--- a/pango/pangofc-shape.c
+++ b/pango/pangofc-shape.c
@@ -97,6 +97,16 @@ pango_fc_hb_font_get_nominal_glyph (hb_font_t *font, void *font_data,
         }
     }
 
+  if (context->shape_flags & PANGO_SHAPE_SHOW_SPACE)
+    {
+      if (unicode == 0x20)
+        {
+          *glyph = pango_fc_font_get_glyph (fc_font, 0x2423);
+          if (*glyph)
+            return TRUE;
+        }
+    }
+
   *glyph = pango_fc_font_get_glyph (fc_font, unicode);
   if (G_LIKELY (*glyph))
     return TRUE;
@@ -354,6 +364,8 @@ _pango_fc_shape (PangoFont           *font,
   PangoGlyphInfo *infos;
   const char *variations;
   PangoShapeFlags shape_flags;
+  PangoGlyph space_glyph;
+  PangoGlyph visible_space_glyph;
 
   g_return_if_fail (font != NULL);
   g_return_if_fail (analysis != NULL);
@@ -504,9 +516,29 @@ _pango_fc_shape (PangoFont           *font,
   pango_glyph_string_set_size (glyphs, num_glyphs);
   infos = glyphs->glyphs;
   last_cluster = -1;
+
+  if (shape_flags & PANGO_SHAPE_SHOW_SPACE)
+    {
+      space_glyph = pango_fc_font_get_glyph (fc_font, 0x20);
+      visible_space_glyph = pango_fc_font_get_glyph (fc_font, 0x2423);
+    }
+
   for (i = 0; i < num_glyphs; i++)
     {
       infos[i].glyph = hb_glyph->codepoint;
+
+      if (shape_flags & PANGO_SHAPE_SHOW_SPACE)
+        {
+          /* harfbuzz replaces ignorables with space, and
+           * we don't want those to show up as visible space.
+           * So check that the visible space comes from a
+           * space in the input. If it doesn't, turn it back
+           * into regular space.
+           */
+          if (hb_glyph->codepoint == visible_space_glyph &&
+              paragraph_text[hb_glyph->cluster] != ' ')
+            infos[i].glyph = space_glyph;
+        }
       glyphs->log_clusters[i] = hb_glyph->cluster - item_offset;
       infos[i].attr.is_cluster_start = glyphs->log_clusters[i] != last_cluster;
       hb_glyph++;