render: refactor to allow setting only selection bg or fg

Before this, we only applied custom selection colors, if *both* the
selection bg and fg had been set.

Since the options are already split up into two separate options, and
since it makes sense to at least be able to keep the foreground colors
unchanged (i.e. only setting the selection background), let's allow
only having one of the selection colors set.

Closes #1846

CHANGELOG.md

@@ -103,6 +103,10 @@
   current alpha value is, unchanged.
 * `gamma-correct-blending=yes` now defaults to `16-bit` image buffers,
   instead of `10-bit`.
+* Allow setting either selection background, or selection foreground,
+  only ([#1846][1846]).
+
+[1846]: https://codeberg.org/dnkl/foot/issues/1846
 
 
 ### Deprecated

config.c

@@ -3403,7 +3403,6 @@ config_load(struct config *conf, const char *conf_path,
                 .cursor = 0,
             },
             .use_custom = {
-                .selection = false,
                 .jump_label = false,
                 .scrollback_indicator = false,
                 .url = false,
@@ -3593,10 +3592,6 @@ config_load(struct config *conf, const char *conf_path,
     if (!config_override_apply(conf, overrides, errors_are_fatal))
         ret = !errors_are_fatal;
 
-    conf->colors.use_custom.selection =
-        conf->colors.selection_fg >> 24 == 0 &&
-        conf->colors.selection_bg >> 24 == 0;
-
     if (ret && conf->fonts[0].count == 0) {
         struct config_font font;
         if (!config_font_parse("monospace", &font)) {

config.h

@@ -180,7 +180,6 @@ struct color_theme {
 
     struct {
         bool cursor:1;
-        bool selection:1;
         bool jump_label:1;
         bool scrollback_indicator:1;
         bool url:1;

doc/foot.ini.5.scd

@@ -1069,8 +1069,7 @@ dark theme (since the default theme is dark).
 
 *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
-	used. Default: _inverse foreground/background_.
+	text. Default: _inverse foreground/background_.
 
 *jump-labels*
 	Two color values specifying the foreground (text) and background

osc.c

@@ -1480,12 +1480,10 @@ osc_dispatch(struct terminal *term)
 
         case 17:
             term->colors.selection_bg = color;
-            term->colors.use_custom_selection = true;
             break;
 
         case 19:
             term->colors.selection_fg = color;
-            term->colors.use_custom_selection = true;
             break;
         }
 
@@ -1589,13 +1587,11 @@ osc_dispatch(struct terminal *term)
     case 117:
         LOG_DBG("resetting selection background color");
         term->colors.selection_bg = term->conf->colors.selection_bg;
-        term->colors.use_custom_selection = term->conf->colors.use_custom.selection;
         break;
 
     case 119:
         LOG_DBG("resetting selection foreground color");
         term->colors.selection_fg = term->conf->colors.selection_fg;
-        term->colors.use_custom_selection = term->conf->colors.use_custom.selection;
         break;
 
     case 133:

render.c

@@ -694,51 +694,75 @@ render_cell(struct terminal *term, pixman_image_t *pix,
     const int x = term->margins.left + col * width;
     const int y = term->margins.top + row_no * height;
 
-    bool is_selected = cell->attrs.selected;
-
     uint32_t _fg = 0;
     uint32_t _bg = 0;
 
     uint16_t alpha = 0xffff;
+    const bool is_selected = cell->attrs.selected;
+
+    /* Use cell specific color, if set, otherwise the default colors (possible reversed) */
+    switch (cell->attrs.fg_src) {
+    case COLOR_RGB:
+        _fg = cell->attrs.fg;
+        break;
+
+    case COLOR_BASE16:
+    case COLOR_BASE256:
+        xassert(cell->attrs.fg < ALEN(term->colors.table));
+        _fg = term->colors.table[cell->attrs.fg];
+        break;
+
+    case COLOR_DEFAULT:
+        _fg = term->reverse ? term->colors.bg : term->colors.fg;
+        break;
+    }
+
+    switch (cell->attrs.bg_src) {
+    case COLOR_RGB:
+        _bg = cell->attrs.bg;
+        break;
+
+    case COLOR_BASE16:
+    case COLOR_BASE256:
+        xassert(cell->attrs.bg < ALEN(term->colors.table));
+        _bg = term->colors.table[cell->attrs.bg];
+        break;
+
+    case COLOR_DEFAULT:
+        _bg = term->reverse ? term->colors.fg : term->colors.bg;
+        break;
+    }
+
+    if (unlikely(is_selected)) {
+        const uint32_t cell_fg = _fg;
+        const uint32_t cell_bg = _bg;
+
+        const bool custom_fg = term->colors.selection_fg >> 24 == 0;
+        const bool custom_bg = term->colors.selection_bg >> 24 == 0;
+        const bool custom_both = custom_fg && custom_bg;
+
+        if (custom_both) {
+            _fg = term->colors.selection_fg;
+            _bg = term->colors.selection_bg;
+        } else if (custom_bg) {
+            _bg = term->colors.selection_bg;
+            _fg = cell->attrs.reverse ? cell_bg : cell_fg;
+        } else if (custom_fg) {
+            _fg = term->colors.selection_fg;
+            _bg = cell->attrs.reverse ? cell_fg : cell_bg;
+        } else {
+            _bg = cell_fg;
+            _fg = cell_bg;
+        }
+
+        if (unlikely(_fg == _bg)) {
+            /* Invert bg when selected/highlighted text has same fg/bg */
+            _bg = ~_bg;
+            alpha = 0xffff;
+        }
 
-    if (is_selected && term->colors.use_custom_selection) {
-        _fg = term->colors.selection_fg;
-        _bg = term->colors.selection_bg;
     } else {
-        /* Use cell specific color, if set, otherwise the default colors (possible reversed) */
-        switch (cell->attrs.fg_src) {
-        case COLOR_RGB:
-            _fg = cell->attrs.fg;
-            break;
-
-        case COLOR_BASE16:
-        case COLOR_BASE256:
-            xassert(cell->attrs.fg < ALEN(term->colors.table));
-            _fg = term->colors.table[cell->attrs.fg];
-            break;
-
-        case COLOR_DEFAULT:
-            _fg = term->reverse ? term->colors.bg : term->colors.fg;
-            break;
-        }
-
-        switch (cell->attrs.bg_src) {
-        case COLOR_RGB:
-            _bg = cell->attrs.bg;
-            break;
-
-        case COLOR_BASE16:
-        case COLOR_BASE256:
-            xassert(cell->attrs.bg < ALEN(term->colors.table));
-            _bg = term->colors.table[cell->attrs.bg];
-            break;
-
-        case COLOR_DEFAULT:
-            _bg = term->reverse ? term->colors.fg : term->colors.bg;
-            break;
-        }
-
-        if (cell->attrs.reverse ^ is_selected) {
+        if (unlikely(cell->attrs.reverse)) {
             uint32_t swap = _fg;
             _fg = _bg;
             _bg = swap;
@@ -806,12 +830,6 @@ render_cell(struct terminal *term, pixman_image_t *pix,
         }
     }
 
-    if (unlikely(is_selected && _fg == _bg)) {
-        /* Invert bg when selected/highlighted text has same fg/bg */
-        _bg = ~_bg;
-        alpha = 0xffff;
-    }
-
     if (cell->attrs.dim)
         _fg = color_dim(term, _fg);
     if (term->conf->bold_in_bright.enabled && cell->attrs.bold)

terminal.c

@@ -1312,7 +1312,6 @@ term_init(const struct config *conf, struct fdm *fdm, struct reaper *reaper,
             .cursor_bg = (theme->use_custom.cursor ? 1u << 31 : 0) | theme->cursor.cursor,
             .selection_fg = theme->selection_fg,
             .selection_bg = theme->selection_bg,
-            .use_custom_selection = theme->use_custom.selection,
             .active_theme = conf->initial_color_theme,
         },
         .color_stack = {
@@ -4714,6 +4713,5 @@ term_theme_apply(struct terminal *term, const struct color_theme *theme)
     term->colors.cursor_bg = (theme->use_custom.cursor ? 1u << 31 : 0) | theme->cursor.cursor;
     term->colors.selection_fg = theme->selection_fg;
     term->colors.selection_bg = theme->selection_bg;
-    term->colors.use_custom_selection = theme->use_custom.selection;
     memcpy(term->colors.table, theme->table, sizeof(term->colors.table));
 }

terminal.h

@@ -404,7 +404,6 @@ struct colors {
     uint32_t cursor_bg;  /* cursor color */
     uint32_t selection_fg;
     uint32_t selection_bg;
-    bool use_custom_selection;
     enum which_color_theme active_theme;
 };