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Re: font sizes


From: Ben Pfaff
Subject: Re: font sizes
Date: Tue, 29 Jun 2010 17:01:38 -0700
User-agent: Gnus/5.13 (Gnus v5.13) Emacs/23.2 (gnu/linux)

John Darrington <address@hidden> writes:

> The function pango_cairo_create_context doesn't exist on the pango
> version shipped with debian lenny.
>
> I had to change it to :
>
>   PangoFontMap *fm = pango_cairo_font_map_get_default ();
>   PangoContext *context = pango_cairo_font_map_create_context 
> (PANGO_CAIRO_FONT_MAP (fm));
>
> Also, I suggest this is taken out of the for() loop.

Thanks.  I'm appending a full diff against "master" with these changes.

> Shouldn't we also unref context ?

I've now done that too.  (I actually had thought of this before,
but I couldn't find a pango_context_unref().  I hadn't realized
that PangoContext was a GObject.)

--8<--------------------------cut here-------------------------->8--

>From 47e2b1135eaaf7a43915326cd854a6479ed81c42 Mon Sep 17 00:00:00 2001
From: Ben Pfaff <address@hidden>
Date: Tue, 29 Jun 2010 16:59:42 -0700
Subject: [PATCH] cairo: Fix handling of font sizes.

Until now this code used pango_font_description_set_absolute_size() to set
the font size.  This sets the font size in device units, e.g. pixels on a
display.  But font sizes are actual specified by the user in points, so
we should instead use pango_font_description_get_size().  This commit
makes that change.

That change is simple, but it necessitates a larger change.
Until now the cairo driver has just assumed that the size of a font is
the size that we assigned it.  But this is no longer the case, since
points and pixels are now different.  So now we measure the actual width
and height of characters and use those as the font size.  At the same
time, the code no longer ignores font sizes included as part of font
description strings, and allows different fonts to have different sizes.

With plenty of help from John Darrington.
---
 src/output/cairo.c         |  164 +++++++++++++++++++++++++++-----------------
 tests/output/render-test.c |    2 +-
 2 files changed, 102 insertions(+), 64 deletions(-)

diff --git a/src/output/cairo.c b/src/output/cairo.c
index a2b7a2f..d4f31aa 100644
--- a/src/output/cairo.c
+++ b/src/output/cairo.c
@@ -95,10 +95,8 @@ enum xr_font_type
 /* A font for use with Cairo. */
 struct xr_font
   {
-    char *string;
     PangoFontDescription *desc;
     PangoLayout *layout;
-    PangoFontMetrics *metrics;
   };
 
 /* An output item whose rendering is in progress. */
@@ -120,7 +118,6 @@ struct xr_driver
 
     /* User parameters. */
     struct xr_font fonts[XR_N_FONTS];
-    int font_height;            /* In XR units. */
 
     int width;                  /* Page width minus margins. */
     int length;                 /* Page length minus margins and header. */
@@ -136,6 +133,7 @@ struct xr_driver
 
     /* Internal state. */
     struct render_params *params;
+    int char_width, char_height;
     char *command_name;
     char *title;
     char *subtitle;
@@ -150,9 +148,6 @@ static const struct output_driver_class cairo_driver_class;
 static void xr_driver_destroy_fsm (struct xr_driver *);
 static void xr_driver_run_fsm (struct xr_driver *);
 
-static bool load_font (struct xr_driver *, struct xr_font *);
-static void free_font (struct xr_font *);
-
 static void xr_draw_line (void *, int bb[TABLE_N_AXES][2],
                           enum render_line_style styles[TABLE_N_AXES][2]);
 static void xr_measure_cell_width (void *, const struct table_cell *,
@@ -182,23 +177,58 @@ opt (struct output_driver *d, struct string_map *options, 
const char *key,
   return driver_option_get (d, options, key, default_value);
 }
 
+static PangoFontDescription *
+parse_font (struct output_driver *d, struct string_map *options,
+            const char *key, const char *default_value,
+            int default_points)
+{
+  PangoFontDescription *desc;
+  char *string;
+
+  /* Parse KEY as a font description. */
+  string = parse_string (opt (d, options, key, default_value));
+  desc = pango_font_description_from_string (string);
+  if (desc == NULL)
+    {
+      error (0, 0, _("\"%s\": bad font specification"), string);
+
+      /* Fall back to DEFAULT_VALUE, which had better be a valid font
+         description. */
+      desc = pango_font_description_from_string (default_value);
+      assert (desc != NULL);
+    }
+  free (string);
+
+  /* If the font description didn't include an explicit font size, then set it
+     to DEFAULT_POINTS. */
+  if (!(pango_font_description_get_set_fields (desc) & PANGO_FONT_MASK_SIZE))
+    pango_font_description_set_size (desc,
+                                     default_points / 1000.0 * PANGO_SCALE);
+
+  return desc;
+}
+
 static struct xr_driver *
 xr_allocate (const char *name, int device_type, struct string_map *o)
 {
   int paper_width, paper_length;
   struct output_driver *d;
   struct xr_driver *xr;
+  int font_points;
 
   xr = xzalloc (sizeof *xr);
   d = &xr->driver;
   output_driver_init (d, &cairo_driver_class, name, device_type);
-  xr->font_height = XR_POINT * 10;
-  xr->fonts[XR_FONT_FIXED].string
-    = parse_string (opt (d, o, "fixed-font", "monospace"));
-  xr->fonts[XR_FONT_PROPORTIONAL].string
-    = parse_string (opt (d, o, "prop-font", "serif"));
-  xr->fonts[XR_FONT_EMPHASIS].string
-    = parse_string (opt (d, o, "emph-font", "serif italic"));
+
+  font_points = parse_int (opt (d, o, "font-size", "10000"),
+                           1000, 1000000);
+  xr->fonts[XR_FONT_FIXED].desc = parse_font (d, o, "fixed-font", "monospace",
+                                              font_points);
+  xr->fonts[XR_FONT_PROPORTIONAL].desc = parse_font (d, o, "prop-font",
+                                                     "serif", font_points);
+  xr->fonts[XR_FONT_EMPHASIS].desc = parse_font (d, o, "emph-font",
+                                                 "serif italic", font_points);
+
   xr->line_gutter = XR_POINT;
   xr->line_space = XR_POINT;
   xr->line_width = XR_POINT / 2;
@@ -217,17 +247,56 @@ xr_allocate (const char *name, int device_type, struct 
string_map *o)
 }
 
 static bool
+xr_is_72dpi (cairo_t *cr)
+{
+  cairo_surface_type_t type;
+  cairo_surface_t *surface;
+
+  surface = cairo_get_target (cr);
+  type = cairo_surface_get_type (surface);
+  return type == CAIRO_SURFACE_TYPE_PDF || type == CAIRO_SURFACE_TYPE_PS;
+}
+
+static bool
 xr_set_cairo (struct xr_driver *xr, cairo_t *cairo)
 {
+  PangoContext *context;
+  PangoFontMap *map;
   int i;
 
   xr->cairo = cairo;
 
   cairo_set_line_width (xr->cairo, xr_to_pt (xr->line_width));
 
+  map = pango_cairo_font_map_get_default ();
+  context = pango_cairo_font_map_create_context (PANGO_CAIRO_FONT_MAP (map));
+  if (xr_is_72dpi (cairo))
+    {
+      /* Pango seems to always scale fonts according to the DPI specified
+         in the font map, even if the surface has a real DPI.  The default
+         DPI is 96, so on a 72 DPI device fonts end up being 96/72 = 133%
+         of their desired size.  We deal with this by fixing the resolution
+         here.  Presumably there is a better solution, but what? */
+      pango_cairo_context_set_resolution (context, 72.0);
+    }
+
+  xr->char_width = 0;
+  xr->char_height = 0;
   for (i = 0; i < XR_N_FONTS; i++)
-    if (!load_font (xr, &xr->fonts[i]))
-      return false;
+    {
+      struct xr_font *font = &xr->fonts[i];
+      int char_width, char_height;
+
+      font->layout = pango_layout_new (context);
+      pango_layout_set_font_description (font->layout, font->desc);
+
+      pango_layout_set_text (font->layout, "0", 1);
+      pango_layout_get_size (font->layout, &char_width, &char_height);
+      xr->char_width = MAX (xr->char_width, char_width);
+      xr->char_height = MAX (xr->char_height, char_height);
+    }
+
+  g_object_unref (G_OBJECT (context));
 
   if (xr->params == NULL)
     {
@@ -241,8 +310,8 @@ xr_set_cairo (struct xr_driver *xr, cairo_t *cairo)
       xr->params->aux = xr;
       xr->params->size[H] = xr->width;
       xr->params->size[V] = xr->length;
-      xr->params->font_size[H] = xr->font_height / 2; /* XXX */
-      xr->params->font_size[V] = xr->font_height;
+      xr->params->font_size[H] = xr->char_width;
+      xr->params->font_size[V] = xr->char_height;
 
       single_width = 2 * xr->line_gutter + xr->line_width;
       double_width = 2 * xr->line_gutter + xr->line_space + 2 * xr->line_width;
@@ -300,23 +369,23 @@ xr_create (const char *file_name, enum 
settings_output_devices device_type,
   cairo_save (xr->cairo);
   xr_driver_next_page (xr, xr->cairo);
 
-  if (xr->width / (xr->font_height / 2) < MIN_WIDTH)
+  if (xr->width / xr->char_width < MIN_WIDTH)
     {
       error (0, 0, _("The defined page is not wide enough to hold at least %d "
                      "characters in the default font.  In fact, there's only "
                      "room for %d characters."),
              MIN_WIDTH,
-             xr->width / (xr->font_height / 2));
+             xr->width / xr->char_width);
       goto error;
     }
 
-  if (xr->length / xr->font_height < MIN_LENGTH)
+  if (xr->length / xr->char_height < MIN_LENGTH)
     {
       error (0, 0, _("The defined page is not long enough to hold at least %d "
                      "lines in the default font.  In fact, there's only "
                      "room for %d lines."),
              MIN_LENGTH,
-             xr->length / xr->font_height);
+             xr->length / xr->char_height);
       goto error;
     }
 
@@ -371,7 +440,15 @@ xr_destroy (struct output_driver *driver)
 
   free (xr->command_name);
   for (i = 0; i < XR_N_FONTS; i++)
-    free_font (&xr->fonts[i]);
+    {
+      struct xr_font *font = &xr->fonts[i];
+
+      if (font->desc != NULL)
+        pango_font_description_free (font->desc);
+      if (font->layout != NULL)
+        g_object_unref (font->layout);
+    }
+
   free (xr->params);
   free (xr);
 }
@@ -764,45 +841,6 @@ xr_layout_cell (struct xr_driver *xr, const struct 
table_cell *cell,
     }
 }
 
-/* Attempts to load FONT, initializing its other members based on
-   its 'string' member and the information in DRIVER.  Returns true
-   if successful, otherwise false. */
-static bool
-load_font (struct xr_driver *xr, struct xr_font *font)
-{
-  PangoContext *context;
-  PangoLanguage *language;
-
-  font->desc = pango_font_description_from_string (font->string);
-  if (font->desc == NULL)
-    {
-      error (0, 0, _("\"%s\": bad font specification"), font->string);
-      return false;
-    }
-  pango_font_description_set_absolute_size (font->desc, xr->font_height);
-
-  font->layout = pango_cairo_create_layout (xr->cairo);
-  pango_layout_set_font_description (font->layout, font->desc);
-
-  language = pango_language_get_default ();
-  context = pango_layout_get_context (font->layout);
-  font->metrics = pango_context_get_metrics (context, font->desc, language);
-
-  return true;
-}
-
-/* Frees FONT. */
-static void
-free_font (struct xr_font *font)
-{
-  free (font->string);
-  if (font->desc != NULL)
-    pango_font_description_free (font->desc);
-  pango_font_metrics_unref (font->metrics);
-  if (font->layout != NULL)
-    g_object_unref (font->layout);
-}
-
 struct output_driver_factory pdf_driver_factory = { "pdf", xr_pdf_create };
 struct output_driver_factory ps_driver_factory = { "ps", xr_ps_create };
 struct output_driver_factory svg_driver_factory = { "svg", xr_svg_create };
@@ -1097,7 +1135,7 @@ xr_render_table (struct xr_driver *xr, const struct 
table_item *table_item)
   ts->table_item = table_item_ref (table_item);
 
   if (xr->y > 0)
-    xr->y += xr->font_height;
+    xr->y += xr->char_height;
 
   page = xr_render_table_item (xr, table_item, &ts->caption_height);
   xr->params->size[V] = xr->length - ts->caption_height;
@@ -1212,7 +1250,7 @@ xr_render_text (struct xr_driver *xr, const struct 
text_item *text_item)
 
     case TEXT_ITEM_BLANK_LINE:
       if (xr->y > 0)
-        xr->y += xr->font_height;
+        xr->y += xr->char_height;
       break;
 
     case TEXT_ITEM_EJECT_PAGE:
diff --git a/tests/output/render-test.c b/tests/output/render-test.c
index 4863eae..e325dbb 100644
--- a/tests/output/render-test.c
+++ b/tests/output/render-test.c
@@ -109,7 +109,7 @@ configure_drivers (int width, int length)
   string_map_insert (&options, "left-margin", "0");
   string_map_insert (&options, "right-margin", "0");
   string_map_insert_nocopy (&options, xstrdup ("paper-size"),
-                            xasprintf ("%dx%dpt", width * 5, length * 6));
+                            xasprintf ("%dx%dpt", width * 5, length * 8));
   driver = output_driver_create (&options);
   if (driver == NULL)
     exit (EXIT_FAILURE);
-- 
1.7.1


-- 
Ben Pfaff 
http://benpfaff.org



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