[pango/pango2] Add an example for optical margins

[Matthias Clasen <matthiasc src gnome org>]

commit 09da1b625e8e86fc4328141617025460733841bc
Author: Matthias Clasen <mclasen redhat com>
Date:   Tue Aug 30 21:08:21 2022 -0400

    Add an example for optical margins
    
    This is currently just using some hardcoded
    heuristics. Once harfbuzz gets a suitable api,
    it can be amended to use lfbd and rtbd features
    from the font where available.

 examples/meson.build       |   1 +
 examples/optical-margins.c | 267 +++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 268 insertions(+)
---
diff --git a/examples/meson.build b/examples/meson.build
index 4455a2a6f..04b3c727e 100644
--- a/examples/meson.build
+++ b/examples/meson.build
@@ -8,6 +8,7 @@ examples += [
   'parshape',
   'columns',
   'userfont',
+  'optical-margins',
 ]
 
 examples_deps = [ libpango_dep ]
diff --git a/examples/optical-margins.c b/examples/optical-margins.c
new file mode 100644
index 000000000..3f93b83df
--- /dev/null
+++ b/examples/optical-margins.c
@@ -0,0 +1,267 @@
+#include <pango2/pangocairo.h>
+
+static int
+get_bound (Pango2Font  *font,
+           gunichar     ch)
+{
+  float f;
+  hb_codepoint_t glyph;
+  Pango2Rectangle ink_rect;
+
+  switch (ch)
+    {
+    case '"':
+    case '\'':
+    case ',':
+    case '.':
+    case 0x2018:
+    case 0x2019:
+    case 0x201A:
+    case 0x201B:
+    case 0x201C:
+    case 0x201D:
+    case 0x201E:
+    case 0x201F:
+      f = 1.0;
+      break;
+    case '-':
+    case 0x2010:
+    case 0x2011:
+    case 0x2012:
+      f = 0.75;
+      break;
+    case '/':
+    case 0x2013:
+      f = 0.50;
+      break;
+    case 0x2014:
+    case 0x2015:
+      f = 0.25;
+      break;
+    case 'A':
+    case 'T':
+    case 'V':
+    case 'W':
+    case 'Y':
+      f = 0.2;
+      break;
+    case 'C':
+    case 'O':
+    case 'c':
+    case 'o':
+    case 'e':
+    case 'w':
+    case 'y':
+      f = 0.1;
+      break;
+    default:
+      f = 0;
+      break;
+    }
+
+  hb_font_get_nominal_glyph (pango2_font_get_hb_font (font), ch, &glyph);
+  pango2_font_get_glyph_extents (font, glyph, &ink_rect, NULL);
+
+  return (int) (ink_rect.width * f);
+}
+
+static int
+get_left_bound (Pango2Font *font,
+                gunichar    ch)
+{
+  /* here is where we would use font-specific information from lfbd */
+  return get_bound (font, ch);
+}
+
+static int
+get_right_bound (Pango2Font *font,
+                 gunichar    ch)
+{
+  /* here is where we would use font-specific information from rtbd */
+  return get_bound (font, ch);
+}
+
+static void
+get_optical_bounds (Pango2Line *line,
+                    int        *left,
+                    int        *right)
+{
+  int start, length;
+  const char *text;
+  gunichar ch;
+  Pango2Run **runs;
+  Pango2Run *run;
+  Pango2Item *item;
+  Pango2Font *font;
+
+  *left = *right = 0;
+
+  if (pango2_line_get_run_count (line) == 0)
+    return;
+
+  text = pango2_line_get_text (line, &start, &length);
+
+  ch = g_utf8_get_char (text + start);
+
+  runs = pango2_line_get_runs (line);
+
+  run = runs[0];
+  item = pango2_run_get_item (run);
+  font = pango2_analysis_get_font (pango2_item_get_analysis (item));
+
+  *left = get_left_bound (font, ch);
+
+  if (pango2_line_is_hyphenated (line))
+    ch = 0x2010;
+  else
+    {
+      char *p = g_utf8_prev_char (text + start + length);
+      ch = g_utf8_get_char (p);
+      if (g_unichar_isspace (ch))
+        {
+          p = g_utf8_prev_char (p);
+          ch = g_utf8_get_char (p);
+        }
+    }
+
+  run = runs[pango2_line_get_run_count (line) - 1];
+  item = pango2_run_get_item (run);
+  font = pango2_analysis_get_font (pango2_item_get_analysis (item));
+
+  *right = get_right_bound (font, ch);
+}
+
+int
+main (int argc, char *argv[])
+{
+  gboolean opt_show_margins = FALSE;
+  GOptionEntry option_entries[] = {
+  { "show-margins", 0, 0, G_OPTION_ARG_NONE, &opt_show_margins, "Show margins", NULL },
+  { NULL, }
+  };
+  GOptionContext *option_context;
+  const char *filename;
+  Pango2Context *context;
+  Pango2LineBreaker *breaker;
+  int margin;
+  int x, y, width;
+  int x0, y0;
+  Pango2Lines *lines;
+  cairo_surface_t *surface;
+  cairo_t *cr;
+  cairo_status_t status;
+  char *text;
+  gsize length;
+  Pango2AttrList *attrs;
+  GError *error = NULL;
+  int left, right;
+
+  option_context = g_option_context_new ("");
+  g_option_context_add_main_entries (option_context, option_entries, NULL);
+  if (!g_option_context_parse (option_context, &argc, &argv, &error))
+    {
+      if (error != NULL)
+        g_printerr ("%s\n", error->message);
+      else
+        g_printerr ("Option parse error\n");
+      exit (1);
+    }
+  g_option_context_free (option_context);
+
+  if (argc != 3)
+    {
+      g_printerr ("Usage: %s [OPTIONS] INPUT_FILENAME OUTPUT_FILENAME\n", argv[0]);
+      return 1;
+    }
+
+  if (!g_file_get_contents (argv[1], &text, &length, &error))
+    {
+      g_printerr ("%s\n", error->message);
+      return 1;
+    }
+
+  filename = argv[2];
+
+  context = pango2_context_new ();
+
+  margin = 20;
+  width = (600 - 2 * margin);
+
+  surface = cairo_image_surface_create (CAIRO_FORMAT_ARGB32, 600, 600);
+  cr = cairo_create (surface);
+  cairo_set_source_rgb (cr, 1, 1, 1);
+  cairo_paint (cr);
+
+  if (opt_show_margins)
+    {
+      cairo_set_source_rgb (cr, 1, 0, 0);
+      cairo_set_line_width (cr, 1);
+      cairo_rectangle (cr, margin + 0.5, -10, width - 1, 620);
+      cairo_stroke (cr);
+    }
+
+  cairo_set_source_rgb (cr, 0, 0, 0);
+
+  breaker = pango2_line_breaker_new (context);
+
+  g_print ("Using %s\n", G_OBJECT_TYPE_NAME (breaker));
+
+  attrs = pango2_attr_list_new ();
+
+  pango2_line_breaker_add_text (breaker, text, -1, attrs);
+
+  pango2_attr_list_unref (attrs);
+
+  lines = pango2_lines_new ();
+
+  x = x0 = margin * PANGO2_SCALE;
+  y = y0 = margin * PANGO2_SCALE;
+  width *= PANGO2_SCALE;
+
+  while (pango2_line_breaker_has_line (breaker))
+    {
+      Pango2Line *line;
+      Pango2Rectangle ext;
+
+      line = pango2_line_breaker_next_line (breaker,
+                                           x, width,
+                                           PANGO2_WRAP_CHAR,
+                                           PANGO2_ELLIPSIZE_NONE);
+
+      get_optical_bounds (line, &left, &right);
+
+      if (!pango2_line_is_paragraph_end (line))
+        line = pango2_line_justify (line, width + left + right);
+
+      pango2_line_get_extents (line, NULL, &ext);
+
+      pango2_lines_add_line (lines, line, x - left, y - ext.y);
+
+      y += ext.height;
+    }
+
+  pango2_cairo_show_lines (cr, lines);
+
+#ifdef CAIRO_HAS_PNG_FUNCTIONS
+  status = cairo_surface_write_to_png (surface, filename);
+#else
+  status = CAIRO_STATUS_PNG_ERROR; /* Not technically correct, but... */
+#endif
+
+  if (status != CAIRO_STATUS_SUCCESS)
+    g_printerr ("Could not save png to '%s'\n", filename);
+  else
+    g_print ("Output written to %s\n", filename);
+
+  g_object_unref (lines);
+  g_object_unref (breaker);
+
+  cairo_surface_destroy (surface);
+  cairo_destroy (cr);
+
+  g_object_unref (context);
+
+  g_free (text);
+
+  return 0;
+}