config: add colors.alpha-non-whitespace option

CHANGELOG.md

@@ -60,6 +60,8 @@
 * Support for `wp_single_pixel_buffer_v1`; certain overlay surfaces
   will now utilize the new single-pixel buffer protocol. This mainly
   reduces the memory usage, but should also be slightly faster.
+* `alpha-non-whitespace` option, allowing for adjustment of
+  transparency only for non whitespace characters.
 
 [1707]: https://codeberg.org/dnkl/foot/issues/1707
 

config.c

@@ -1340,6 +1340,20 @@ parse_section_colors(struct context *ctx)
         return true;
     }
 
+    else if (streq(key, "alpha-non-whitespace")) {
+        float alpha;
+        if (!value_to_float(ctx, &alpha))
+            return false;
+
+        if (alpha < 0. || alpha > 1.) {
+            LOG_CONTEXTUAL_ERR("not in range 0.0-1.0");
+            return false;
+        }
+
+        conf->colors.alpha_non_whitespace = alpha * 65535.;
+        return true;
+    }
+
     else if (streq(key, "flash-alpha")) {
         float alpha;
         if (!value_to_float(ctx, &alpha))
@@ -2854,6 +2868,9 @@ parse_config_file(FILE *f, struct config *conf, const char *path, bool errors_ar
         errno = 0;
     }
 
+    /* Set `alpha_non_whitespace` to atleast `alpha`. */
+    conf->colors.alpha_non_whitespace = max(conf->colors.alpha_non_whitespace, conf->colors.alpha);
+
     if (errno != 0) {
         LOG_AND_NOTIFY_ERRNO("failed to read from configuration");
         if (errors_are_fatal)
@@ -3092,6 +3109,12 @@ config_load(struct config *conf, const char *conf_path,
             .flash = 0x7f7f00,
             .flash_alpha = 0x7fff,
             .alpha = 0xffff,
+            /* HACK:
+             * when `alpha_non_whitespace` is not set its
+             * default value will be `alpha`. This is achived via
+             * restricting it to be at least the value of `alpha`
+             */
+            .alpha_non_whitespace = 0x0000,
             .selection_fg = 0x80000000,  /* Use default bg */
             .selection_bg = 0x80000000,  /* Use default fg */
             .use_custom = {

config.h

@@ -220,6 +220,7 @@ struct config {
         uint32_t flash_alpha;
         uint32_t table[256];
         uint16_t alpha;
+        uint16_t alpha_non_whitespace;
         uint32_t selection_fg;
         uint32_t selection_bg;
         uint32_t url;

doc/foot.ini.5.scd

@@ -647,6 +647,12 @@ can configure the background transparency with the _alpha_ option.
 	Background translucency. A value in the range 0.0-1.0, where 0.0
 	means completely transparent, and 1.0 is opaque. Default: _1.0_.
 
+*alpha-non-whitespace*
+	Background translucency for non whitespace characters.
+	A value in the range 0.0-1.0, where 0.0 means completely
+	transparent, and 1.0 is opaque. Default: The value of 0.0.
+	If this value is lower than _alpha_, _alpha_ will be used instead.
+
 *selection-foreground*, *selection-background*
 	Foreground (text) and background color to use in selected
 	text. Note that *both* options must be set, or the default will be

foot.ini

@@ -77,6 +77,7 @@
 
 [colors]
 # alpha=1.0
+# alpha-non-whitespace=1.0
 # background=242424
 # foreground=ffffff
 # flash=7f7f00

render.c

@@ -2,6 +2,7 @@
 
 #include <string.h>
 #include <wctype.h>
+#include <ctype.h>
 #include <unistd.h>
 #include <signal.h>
 
@@ -572,8 +573,10 @@ render_cell(struct terminal *term, pixman_image_t *pix, pixman_region32_t *damag
                  * NOTE: if changing this, also update render_margin()
                  */
                 xassert(alpha == 0xffff);
-            } else {
+            } else if (isspace(cell->wc) || cell->wc == 0) {
                 alpha = term->colors.alpha;
+            } else {
+                alpha = term->colors.alpha_non_whitespace;
             }
         }
     }

terminal.c

@@ -1221,6 +1221,7 @@ term_init(const struct config *conf, struct fdm *fdm, struct reaper *reaper,
             .fg = conf->colors.fg,
             .bg = conf->colors.bg,
             .alpha = conf->colors.alpha,
+            .alpha_non_whitespace = conf->colors.alpha_non_whitespace,
             .selection_fg = conf->colors.selection_fg,
             .selection_bg = conf->colors.selection_bg,
             .use_custom_selection = conf->colors.use_custom.selection,

terminal.h

@@ -516,6 +516,7 @@ struct terminal {
         uint32_t bg;
         uint32_t table[256];
         uint16_t alpha;
+        uint16_t alpha_non_whitespace;
         uint32_t selection_fg;
         uint32_t selection_bg;
         bool use_custom_selection;