Subject: bug#54564: 29.0.50; [PATCH] Use gsettings font rendering entries for pgtk builds

From: Pieter van Prooijen <[email-masked]>
Date: Fri, 25 Mar 2022 12:23:10 +0100

Hello, 

When using the pgtk build of emacs under Wayland/Ubuntu, I noticed that
the font hinting was different from the regular X (Ubuntu supplied)
version of emacs.

I have the gsettings config for font hinting set to "full" on my
system, using the fonts tab in the gnome-tweaks tool.

It looks like Cairo defaults to the "slight" hinting setting when using
the Wayland backend for display and will only use the gsettings config
when rendering to an X backend, when it reads the current font settings
from xrdb.

I've attached a patch (against
380f0443b288c68df3762ee20d78719f08dd92ff) which applies the font
entries from gsettings (if present) when creating a font in Cairo.

Note that this patch won't dynamically re-render when emacs is already
running (like it does when changing the system font).
I made an attempt to hook into the gsettings change callback, but could
not force a re-creation of the font with the changed parameters,for
instance using a 'font-render' config changed event. Any pointers on
how to achieve this?
 
Do you think if this patch is a good approach to get the pgtk build to
use the system preferences for font hinting and anti-aliasing?

Kind Regards,

Pieter van Prooijen
    
From 6fe888e7c14ef5aad124c0d68fcd071cd5b65e81 Mon Sep 17 00:00:00 2001
From: Pieter van Prooijen <[email-masked]>
Date: Fri, 25 Mar 2022 11:47:39 +0100
Subject: [PATCH] Use gsettings font rendering entries for pgtk builds

If present, apply the gsettings font hinting and antialiasing entries
when creating a font in cairo.
* src/xsettings.c, src/xsettings.h: read and apply gsetting entries.
* src/ftcrfont.c: use the font_options from xsettings.c when creating a font.
---
 src/ftcrfont.c  |   6 ++-
 src/xsettings.c | 118 ++++++++++++++++++++++++++++++++++++++++++++++++
 src/xsettings.h |   5 +-
 3 files changed, 127 insertions(+), 2 deletions(-)

diff --git a/src/ftcrfont.c b/src/ftcrfont.c
index 98a28af5f2..b659024524 100644
--- a/src/ftcrfont.c
+++ b/src/ftcrfont.c
@@ -37,6 +37,7 @@
 #include "font.h"
 #include "ftfont.h"
 #include "pdumper.h"
+#include "xsettings.h"
 
 #ifdef USE_BE_CAIRO
 #define RED_FROM_ULONG(color)	(((color) >> 16) & 0xff)
@@ -168,10 +169,13 @@ ftcrfont_open (struct frame *f, Lisp_Object entity, int pixel_size)
   cairo_matrix_t font_matrix, ctm;
   cairo_matrix_init_scale (&font_matrix, pixel_size, pixel_size);
   cairo_matrix_init_identity (&ctm);
-  cairo_font_options_t *options = cairo_font_options_create ();
+
 #ifdef USE_BE_CAIRO
+  cairo_font_options_t *options = cairo_font_options_create();
   if (be_use_subpixel_antialiasing ())
     cairo_font_options_set_antialias (options, CAIRO_ANTIALIAS_SUBPIXEL);
+#else
+  cairo_font_options_t *options = xsettings_get_font_options();
 #endif
   cairo_scaled_font_t *scaled_font
     = cairo_scaled_font_create (font_face, &font_matrix, &ctm, options);
diff --git a/src/xsettings.c b/src/xsettings.c
index 71d02e6152..c72d59e99b 100644
--- a/src/xsettings.c
+++ b/src/xsettings.c
@@ -57,6 +57,7 @@ Copyright (C) 2009-2022 Free Software Foundation, Inc.
 #if defined USE_CAIRO || defined HAVE_XFT
 #ifdef USE_CAIRO
 #include <fontconfig/fontconfig.h>
+#include <cairo.h>
 #else  /* HAVE_XFT */
 #include <X11/Xft/Xft.h>
 #endif
@@ -67,6 +68,10 @@ Copyright (C) 2009-2022 Free Software Foundation, Inc.
 static Display_Info *first_dpyinfo;
 static Lisp_Object current_tool_bar_style;
 
+#ifdef USE_CAIRO
+static cairo_font_options_t *font_options;
+#endif
+
 /* Store a config changed event in to the event queue.  */
 
 static void
@@ -215,11 +220,96 @@ #define GSETTINGS_MONO_FONT  "monospace-font-name"
 #define GSETTINGS_FONT_NAME  "font-name"
 #endif
 
+#ifdef HAVE_PGTK
+#define GSETTINGS_FONT_ANTIALIASING "font-antialiasing"
+#define GSETTINGS_FONT_RGBA_ORDER   "font-rgba-order"
+#define GSETTINGS_FONT_HINTING      "font-hinting"
+#endif
 
 /* The single GSettings instance, or NULL if not connected to GSettings.  */
 
 static GSettings *gsettings_client;
 
+/* For hinting and antialias no dynamic re-display is (yet) possible,
+   because cairo applies these options when creating the font, not when
+   rendering it.
+*/
+
+#ifdef HAVE_PGTK
+/* Apply changes in the hinting system setting */
+static void
+apply_gsettings_font_hinting(GSettings *settings)
+{
+  GVariant *val = g_settings_get_value (settings, GSETTINGS_FONT_HINTING);
+  if (val)
+    {
+      g_variant_ref_sink (val);
+      if (g_variant_is_of_type (val, G_VARIANT_TYPE_STRING))
+	{
+	  const char *hinting = g_variant_get_string (val, NULL);
+
+	  if (strcmp (hinting, "full") == 0)
+	    cairo_font_options_set_hint_style(font_options, CAIRO_HINT_STYLE_FULL);
+	  else if (strcmp (hinting, "medium") == 0)
+	    cairo_font_options_set_hint_style(font_options, CAIRO_HINT_STYLE_MEDIUM);
+	  else if (strcmp (hinting, "slight") == 0)
+	    cairo_font_options_set_hint_style(font_options, CAIRO_HINT_STYLE_SLIGHT);
+	  else if (strcmp (hinting, "none") == 0)
+	    cairo_font_options_set_hint_style(font_options, CAIRO_HINT_STYLE_NONE);
+	}
+      g_variant_unref (val);
+    }
+}
+
+/* Apply changes in the antialiasing system setting */
+static void
+apply_gsettings_font_antialias(GSettings *settings)
+{
+  GVariant *val = g_settings_get_value (settings, GSETTINGS_FONT_ANTIALIASING);
+  if (val)
+    {
+      g_variant_ref_sink (val);
+      if (g_variant_is_of_type (val, G_VARIANT_TYPE_STRING))
+	{
+	  const char *antialias = g_variant_get_string (val, NULL);
+
+	  if (strcmp (antialias, "none") == 0)
+	    cairo_font_options_set_antialias(font_options, CAIRO_ANTIALIAS_NONE);
+	  else if (strcmp(antialias, "grayscale") == 0)
+	    cairo_font_options_set_antialias(font_options, CAIRO_ANTIALIAS_GRAY);
+	  else if (strcmp(antialias, "rgba") == 0)
+	    cairo_font_options_set_antialias(font_options, CAIRO_ANTIALIAS_SUBPIXEL);
+	}
+      g_variant_unref (val);
+    }
+}
+
+/* Apply the settings for the rgb element ordering */
+static void
+apply_gsettings_font_rgba_order(GSettings *settings)
+{
+  GVariant *val = g_settings_get_value (settings, GSETTINGS_FONT_RGBA_ORDER);
+  if (val)
+    {
+      g_variant_ref_sink (val);
+      if (g_variant_is_of_type (val, G_VARIANT_TYPE_STRING))
+	{
+	  const char *rgba_order = g_variant_get_string (val, NULL);
+
+	  if (strcmp (rgba_order, "rgb") == 0)
+	    cairo_font_options_set_subpixel_order(font_options, CAIRO_SUBPIXEL_ORDER_RGB);
+	  else if (strcmp (rgba_order, "bgr") == 0)
+	    cairo_font_options_set_subpixel_order(font_options, CAIRO_SUBPIXEL_ORDER_BGR);
+	  else if (strcmp (rgba_order, "vrgb") == 0)
+	    cairo_font_options_set_subpixel_order(font_options, CAIRO_SUBPIXEL_ORDER_VRGB);
+	  else if (strcmp (rgba_order, "vbgr") == 0)
+	    cairo_font_options_set_subpixel_order(font_options, CAIRO_SUBPIXEL_ORDER_VBGR);
+	}
+      g_variant_unref (val);
+    }
+}
+#endif /* HAVE_PGTK */
+
 /* Callback called when something changed in GSettings.  */
 
 static void
@@ -900,6 +990,18 @@ init_gsettings (void)
         dupstring (&current_font, g_variant_get_string (val, NULL));
       g_variant_unref (val);
     }
+
+  /* Only use the gsettings font entries for non-X cairo backends
+     (which is the recommended way of running pgtk builds).
+     For the X backend cairo will apply these entries itself,
+     reading them from xrdb. */
+#ifdef HAVE_PGTK
+  font_options = cairo_font_options_create ();
+  apply_gsettings_font_antialias(gsettings_client);
+  apply_gsettings_font_hinting(gsettings_client);
+  apply_gsettings_font_rgba_order(gsettings_client);
+#endif /* HAVE_PGTK */
+
 #endif /* USE_CAIRO || HAVE_XFT */
 
 #endif /* HAVE_GSETTINGS */
@@ -1021,6 +1123,18 @@ xsettings_get_system_normal_font (void)
 }
 #endif
 
+#ifdef USE_CAIRO
+/* Return the cairo font options, possibly initialized in
+   init_gsettings() */
+cairo_font_options_t *
+xsettings_get_font_options (void) {
+  if (font_options == NULL)
+    return cairo_font_options_create();
+  else
+    return cairo_font_options_copy(font_options);
+}
+#endif
+
 DEFUN ("font-get-system-normal-font", Ffont_get_system_normal_font,
        Sfont_get_system_normal_font,
        0, 0, 0,
@@ -1073,6 +1187,10 @@ syms_of_xsettings (void)
   gconf_client = NULL;
   PDUMPER_IGNORE (gconf_client);
 #endif
+#ifdef USE_CAIRO
+  font_options = NULL;
+  PDUMPER_IGNORE (font_options);
+#endif
 
   DEFSYM (Qmonospace_font_name, "monospace-font-name");
   DEFSYM (Qfont_name, "font-name");
diff --git a/src/xsettings.h b/src/xsettings.h
index ccaa36489d..15984e8865 100644
--- a/src/xsettings.h
+++ b/src/xsettings.h
@@ -40,6 +40,9 @@ #define XSETTINGS_H
 #ifdef USE_LUCID
 extern const char *xsettings_get_system_normal_font (void);
 #endif
-
+#ifdef USE_CAIRO
+struct cairo_font_options_t;
+extern cairo_font_options_t *xsettings_get_font_options (void);
+#endif
 
 #endif /* XSETTINGS_H */
-- 
2.32.0