config: add tweak.scaling-filter

Use the new fcft_set_scaling_filter() API to use a non-default scaling
filter.

By default, we use lanczo3, the ‘best’ filter. This overrides the
default in fcft, which is ‘cubic’ filtering.

CHANGELOG.md

@@ -91,6 +91,7 @@
 * Minimum window size changed from four rows and 20 columns, to 1 row
   and 2 columns.
 * **scrollback-up/down** renamed to **scrollback-up/down-page**.
+* fcft >= 2.3.0 is now required.
 
 
 ### Fixed

config.c

@@ -1442,7 +1442,34 @@ parse_section_tweak(
     const char *key, const char *value, struct config *conf,
     const char *path, unsigned lineno)
 {
-    if (strcmp(key, "allow-overflowing-double-width-glyphs") == 0) {
+    if (strcmp(key, "scaling-filter") == 0) {
+        static const struct {
+            const char *name;
+            enum fcft_scaling_filter filter;
+        } filters[] = {
+            {"none",     FCFT_SCALING_FILTER_NONE},
+            {"nearest",  FCFT_SCALING_FILTER_NEAREST},
+            {"bilinear", FCFT_SCALING_FILTER_BILINEAR},
+            {"cubic",    FCFT_SCALING_FILTER_CUBIC},
+            {"lanczos3", FCFT_SCALING_FILTER_LANCZOS3},
+        };
+
+        for (size_t i = 0; i < ALEN(filters); i++) {
+            if (strcmp(value, filters[i].name) == 0) {
+                conf->tweak.fcft_filter = filters[i].filter;
+                LOG_WARN("tweak: scaling-filter=%s", filters[i].name);
+                return true;
+            }
+        }
+
+        LOG_AND_NOTIFY_ERR(
+            "%s:%d: [tweak]: %s: invalid 'scaling-filter' value, "
+            "expected one of 'none', 'nearest', 'bilinear', 'cubic' or "
+            "'lanczos3'", path, lineno, value);
+        return false;
+    }
+
+    else if (strcmp(key, "allow-overflowing-double-width-glyphs") == 0) {
         conf->tweak.allow_overflowing_double_width_glyphs = str_to_bool(value);
         if (conf->tweak.allow_overflowing_double_width_glyphs)
             LOG_WARN("tweak: allow overflowing double-width glyphs");
@@ -1894,6 +1921,7 @@ config_load(struct config *conf, const char *conf_path,
         .hold_at_exit = false,
 
         .tweak = {
+            .fcft_filter = FCFT_SCALING_FILTER_LANCZOS3,
             .allow_overflowing_double_width_glyphs = false,
             .delayed_render_lower_ns = 500000,         /* 0.5ms */
             .delayed_render_upper_ns = 16666666 / 2,   /* half a frame period (60Hz) */

config.h

@@ -160,6 +160,7 @@ struct config {
     bool hold_at_exit;
 
     struct {
+        enum fcft_scaling_filter fcft_filter;
         bool allow_overflowing_double_width_glyphs;
         bool render_timer_osd;
         bool render_timer_log;

doc/foot.ini.5.scd

@@ -460,9 +460,21 @@ should not change these unless you understand what they do and note
 that changing the default values *will* print a warning when launching
 foot.
 
+Note that these options may change, or be removed at any time, without
+prior notice.
+
 When reporting bugs, please mention if, and to what, you have changed
 any of these options.
 
+*scaling-filter*
+	Overrides the default scaling filter used when down-scaling bitmap
+	fonts (e.g. emoji fonts). Possible values are *none*, *nearest*,
+	*bilinear*, *cubic* or *lanczos3*. *cubic* and *lanczos3* produce
+	the best results, but are slower (with *lanczos3* being the best
+	_and_ slowest).
+	
+	Default: _lanczos3_.
+
 *allow-overflowing-double-width-glyphs*
 	Boolean. when enabled, double width glyphs with a character width
 	of 1 are allowed to overflow into the neighbouring cell.

main.c

@@ -363,6 +363,8 @@ main(int argc, char *const *argv)
         return EXIT_SUCCESS;
     }
 
+    fcft_set_scaling_filter(conf.tweak.fcft_filter);
+
     setlocale(LC_CTYPE, "");
     LOG_INFO("locale: %s", setlocale(LC_CTYPE, NULL));
     if (!locale_is_utf8()) {

meson.build

@@ -62,7 +62,7 @@ xkb = dependency('xkbcommon')
 fontconfig = dependency('fontconfig')
 
 tllist = dependency('tllist', version: '>=1.0.4', fallback: 'tllist')
-fcft = dependency('fcft', version: ['>=2.2.2', '<3.0.0'], fallback: 'fcft')
+fcft = dependency('fcft', version: ['>=2.3.0', '<3.0.0'], fallback: 'fcft')
 
 wayland_protocols_datadir = wayland_protocols.get_pkgconfig_variable('pkgdatadir')