config: add ‘font-size-adjustment=N[px|%]’ option

This patch adds a new config option, font-size-adjustment.

It lets you configure how much the font size should be
incremented/decremented when zooming in or out (ctrl-+, ctrl+-).

Values can be specified in points, pixels or percent.

Closes #1188

CHANGELOG.md

@@ -52,10 +52,14 @@
 * String values in `foot.ini` may now be quoted. This can be used to
   set a value to the empty string, for example.
 * Environment variables can now be **unset**, by setting
-  `[environment].<variable>=""` (quotes are required) ([#1225][1225])
+  `[environment].<variable>=""` (quotes are required) ([#1225][1225]).
+* `font-size-adjustment=N[px]` option, letting you configure how much
+  to increment/decrement the font size when zooming in or out
+  ([#1188][1188]).
 
 [1136]: https://codeberg.org/dnkl/foot/issues/1136
 [1225]: https://codeberg.org/dnkl/foot/issues/1225
+[1188]: https://codeberg.org/dnkl/foot/issues/1188
 
 
 ### Changed

config.c

@@ -925,6 +925,31 @@ parse_section_main(struct context *ctx)
         return true;
     }
 
+    else if (strcmp(key, "font-size-adjustment") == 0) {
+        const size_t len = strlen(ctx->value);
+        if (len >= 1 && ctx->value[len - 1] == '%') {
+            errno = 0;
+            char *end = NULL;
+
+            float percent = strtof(ctx->value, &end);
+            if (!(errno == 0 && end == ctx->value + len - 1)) {
+                LOG_CONTEXTUAL_ERR(
+                    "invalid percent value (must be in the form 10.5%%)");
+                return false;
+            }
+
+            conf->font_size_adjustment.percent = percent / 100.;
+            conf->font_size_adjustment.pt_or_px.pt = 0;
+            conf->font_size_adjustment.pt_or_px.px = 0;
+            return true;
+        } else {
+            bool ret = value_to_pt_or_px(ctx, &conf->font_size_adjustment.pt_or_px);
+            if (ret)
+                conf->font_size_adjustment.percent = 0.;
+            return ret;
+        }
+    }
+
     else if (strcmp(key, "line-height") == 0)
         return value_to_pt_or_px(ctx, &conf->line_height);
 
@@ -2886,6 +2911,7 @@ config_load(struct config *conf, const char *conf_path,
         },
         .startup_mode = STARTUP_WINDOWED,
         .fonts = {{0}},
+        .font_size_adjustment = {.percent = 0., .pt_or_px = {.pt = 0.5, .px = 0}},
         .line_height = {.pt = 0, .px = -1},
         .letter_spacing = {.pt = 0, .px = 0},
         .horizontal_letter_offset = {.pt = 0, .px = 0},

config.h

@@ -22,6 +22,11 @@ struct pt_or_px {
     float pt;
 };
 
+struct font_size_adjustment {
+    struct pt_or_px pt_or_px;
+    float percent;
+};
+
 enum cursor_style { CURSOR_BLOCK, CURSOR_UNDERLINE, CURSOR_BEAM };
 
 enum conf_size_type {CONF_SIZE_PX, CONF_SIZE_CELLS};
@@ -139,6 +144,7 @@ struct config {
 
     enum {DPI_AWARE_AUTO, DPI_AWARE_YES, DPI_AWARE_NO} dpi_aware;
     struct config_font_list fonts[4];
+    struct font_size_adjustment font_size_adjustment;
 
     /* Custom font metrics (-1 = use real font metrics) */
     struct pt_or_px line_height;

doc/foot.ini.5.scd

@@ -80,6 +80,19 @@ empty string to be set, but it must be quoted: *KEY=""*)
 	Default: _monospace:size=8_ (*font*), _not set_ (*font-bold*,
 	*font-italic*, *font-bold-italic*).
 
+*font-size-adjustment*
+	Amount, in _points_, _pixels_ or _percent_, to increment/decrement
+	the font size when zooming in our out.
+	
+	Examples:
+	```
+	font-size-adjustment=0.5   # Adjust by 0.5 points
+	font-size-adjustment=10xp  # Adjust by 10 pixels
+	font-size-adjustment=7.5%  # Adjust by 7.5 percent
+	```
+	
+	Default: _0.5_
+
 *include*
 	Absolute path to configuration file to import.
 	

terminal.c

@@ -2035,29 +2035,70 @@ term_reset(struct terminal *term, bool hard)
 }
 
 static bool
-term_font_size_adjust(struct terminal *term, double amount)
+term_font_size_adjust_by_points(struct terminal *term, float amount)
 {
     const struct config *conf = term->conf;
-
     const float dpi = term->font_is_sized_by_dpi ? term->font_dpi : 96.;
 
     for (size_t i = 0; i < 4; i++) {
         const struct config_font_list *font_list = &conf->fonts[i];
 
         for (size_t j = 0; j < font_list->count; j++) {
-            float old_pt_size = term->font_sizes[i][j].pt_size;
+            struct config_font *font = &term->font_sizes[i][j];
+            float old_pt_size = font->pt_size;
 
-            /*
+            if (font->px_size > 0)
-             * To ensure primary and user-configured fallback fonts are
+                old_pt_size = font->px_size * 72. / dpi;
-             * resizes by the same amount, convert pixel sizes to point
-             * sizes, and to the adjustment on point sizes only.
-             */
 
-            if (term->font_sizes[i][j].px_size > 0)
+            font->pt_size = fmaxf(old_pt_size + amount, 0.);
-                old_pt_size = term->font_sizes[i][j].px_size * 72. / dpi;
+            font->px_size = -1;
+        }
+    }
 
-            term->font_sizes[i][j].pt_size = fmaxf(old_pt_size + amount, 0.);
+    return reload_fonts(term);
-            term->font_sizes[i][j].px_size = -1;
+}
+
+static bool
+term_font_size_adjust_by_pixels(struct terminal *term, int amount)
+{
+    const struct config *conf = term->conf;
+    const float dpi = term->font_is_sized_by_dpi ? term->font_dpi : 96.;
+
+    for (size_t i = 0; i < 4; i++) {
+        const struct config_font_list *font_list = &conf->fonts[i];
+
+        for (size_t j = 0; j < font_list->count; j++) {
+            struct config_font *font = &term->font_sizes[i][j];
+            int old_px_size = font->px_size;
+
+            if (font->px_size <= 0)
+                old_px_size = font->pt_size * dpi / 72.;
+
+            font->px_size = max(old_px_size + amount, 1);
+        }
+    }
+
+    return reload_fonts(term);
+}
+
+static bool
+term_font_size_adjust_by_percent(struct terminal *term, bool increment, float percent)
+{
+    const struct config *conf = term->conf;
+    const float multiplier = increment
+        ? 1. + percent
+        : 1. / (1. + percent);
+
+    for (size_t i = 0; i < 4; i++) {
+        const struct config_font_list *font_list = &conf->fonts[i];
+
+        for (size_t j = 0; j < font_list->count; j++) {
+            struct config_font *font = &term->font_sizes[i][j];
+
+            if (font->px_size > 0)
+                font->px_size = max(font->px_size * multiplier, 1);
+            else
+                font->pt_size = fmax(font->pt_size * multiplier, 0);
         }
     }
 
@@ -2067,19 +2108,29 @@ term_font_size_adjust(struct terminal *term, double amount)
 bool
 term_font_size_increase(struct terminal *term)
 {
-    if (!term_font_size_adjust(term, 0.5))
+    const struct config *conf = term->conf;
-        return false;
+    const struct font_size_adjustment *inc_dec = &conf->font_size_adjustment;
 
-    return true;
+    if (inc_dec->percent > 0.)
+        return term_font_size_adjust_by_percent(term, true, inc_dec->percent);
+    else if (inc_dec->pt_or_px.px > 0)
+        return term_font_size_adjust_by_pixels(term, inc_dec->pt_or_px.px);
+    else
+        return term_font_size_adjust_by_points(term, inc_dec->pt_or_px.pt);
 }
 
 bool
 term_font_size_decrease(struct terminal *term)
 {
-    if (!term_font_size_adjust(term, -0.5))
+    const struct config *conf = term->conf;
-        return false;
+    const struct font_size_adjustment *inc_dec = &conf->font_size_adjustment;
 
-    return true;
+    if (inc_dec->percent > 0.)
+        return term_font_size_adjust_by_percent(term, false, inc_dec->percent);
+    else if (inc_dec->pt_or_px.px > 0)
+        return term_font_size_adjust_by_pixels(term, -inc_dec->pt_or_px.px);
+    else
+        return term_font_size_adjust_by_points(term, -inc_dec->pt_or_px.pt);
 }
 
 bool

tests/test-config.c

@@ -467,6 +467,7 @@ test_section_main(void)
     test_boolean(&ctx, &parse_section_main, "locked-title", &conf.locked_title);
     test_boolean(&ctx, &parse_section_main, "notify-focus-inhibit", &conf.notify_focus_inhibit);
 
+    test_pt_or_px(&ctx, &parse_section_main, "font-size-adjustment", &conf.font_size_adjustment.pt_or_px);  /* TODO: test ‘N%’ values too */
     test_pt_or_px(&ctx, &parse_section_main, "line-height", &conf.line_height);
     test_pt_or_px(&ctx, &parse_section_main, "letter-spacing", &conf.letter_spacing);
     test_pt_or_px(&ctx, &parse_section_main, "horizontal-letter-offset", &conf.horizontal_letter_offset);