Add background alpha support

config.c

@@ -119,6 +119,19 @@ str_to_ulong(const char *s, int base, unsigned long *res)
     return errno == 0 && *end == '\0';
 }
 
+static bool
+str_to_double(const char *s, double *res)
+{
+    if (s == NULL)
+        return false;
+
+    errno = 0;
+    char *end = NULL;
+
+    *res = strtod(s, &end);
+    return errno == 0 && *end == '\0';
+}
+
 static bool
 str_to_color(const char *s, uint32_t *color, const char *path, int lineno)
 {
@@ -203,6 +216,17 @@ parse_section_colors(const char *key, const char *value, struct config *conf,
     else if (strcmp(key, "bright5") == 0)    color = &conf->colors.bright[5];
     else if (strcmp(key, "bright6") == 0)    color = &conf->colors.bright[6];
     else if (strcmp(key, "bright7") == 0)    color = &conf->colors.bright[7];
+    else if (strcmp(key, "alpha") == 0) {
+        double alpha;
+        if (!str_to_double(value, &alpha) || alpha < 0. || alpha > 1.) {
+            LOG_ERR("%s: %d: alpha: expected a value in the range 0.0-1.0",
+                    path, lineno);
+            return false;
+        }
+
+        conf->colors.alpha = alpha;
+        return true;
+    }
 
     else {
         LOG_ERR("%s:%d: invalid key: %s", path, lineno, key);
@@ -442,6 +466,7 @@ config_load(struct config *conf)
                 default_bright[6],
                 default_bright[7],
             },
+            .alpha = 1.,
         },
 
         .cursor = {

config.h

@@ -18,6 +18,7 @@ struct config {
         uint32_t bg;
         uint32_t regular[8];
         uint32_t bright[8];
+        double alpha;
     } colors;
 
     struct {

doc/foot.5.scd

@@ -71,6 +71,10 @@ in this order:
 	_bfebbf_, _f0dfaf_, _8cd0d3_, _dc8cc3_, _93e0e3_ and _ffffff_ (a
 	variant of the _zenburn_ theme).
 
+*alpha*
+	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_.
+
 # FONT FORMAT
 
 The font is specified in FontConfig syntax. That is, a colon-separated

footrc

@@ -27,3 +27,4 @@
 # bright5=dc8cc3
 # bright6=93e0e3
 # bright7=ffffff
+# alpha=1.0

main.c

@@ -462,6 +462,7 @@ main(int argc, char *const *argv)
                 conf.colors.bright[6],
                 conf.colors.bright[7],
             },
+            .alpha = conf.colors.alpha,
         },
         .default_cursor_style = conf.cursor.style,
         .cursor_style = conf.cursor.style,

render.c

@@ -189,7 +189,7 @@ render_cell(struct terminal *term, cairo_t *cr,
 
     /* Background */
     cairo_set_operator(cr, CAIRO_OPERATOR_SOURCE);
-    cairo_set_source_rgb(cr, bg.r, bg.g, bg.b);
+    cairo_set_source_rgba(cr, bg.r, bg.g, bg.b, block_cursor ? 1.0 : term->colors.alpha);
     cairo_rectangle(cr, x, y, cell_cols * width, height);
     cairo_fill(cr);
 
@@ -432,7 +432,7 @@ grid_render(struct terminal *term)
 
         uint32_t _bg = !term->reverse ? term->colors.bg : term->colors.fg;
         struct rgb bg = color_hex_to_rgb(_bg);
-        cairo_set_source_rgb(buf->cairo[0], bg.r, bg.g, bg.b);
+        cairo_set_source_rgba(buf->cairo[0], bg.r, bg.g, bg.b, term->colors.alpha);
 
         cairo_rectangle(buf->cairo[0], rmargin, 0, rmargin_width, term->height);
         cairo_rectangle(buf->cairo[0], 0, bmargin, term->width, bmargin_height);

terminal.h

@@ -283,6 +283,7 @@ struct terminal {
         uint32_t bg;
         uint32_t regular[8];
         uint32_t bright[8];
+        double alpha;
 
         uint32_t default_fg;
         uint32_t default_bg;