config: add mouse.alternate-scroll-mode option

This option controls the initial state of the Alternate Scroll Mode,
and defaults to ‘enabled’.

CHANGELOG.md

@@ -73,6 +73,12 @@
   (https://codeberg.org/dnkl/foot/issues/128).
 * **scrollback-up-line** and **scrollback-down-line** key
   bindings. They scroll up/down a single line in the scrollback.
+* **mouse.alternate-scroll-mode** option to `foot.ini`. This option
+  controls the initial state of the _Alternate Scroll Mode_, and
+  defaults to `yes`. When enabled, mouse events are translated to
+  up/down key events in the alternate screen, letting you scroll in
+  e.g. `less` and other applications without enabling native mouse
+  support in them (https://codeberg.org/dnkl/foot/issues/135).
 
 
 ### Removed

config.c

@@ -764,6 +764,9 @@ parse_section_mouse(const char *key, const char *value, struct config *conf,
     if (strcmp(key, "hide-when-typing") == 0)
         conf->mouse.hide_when_typing = str_to_bool(value);
 
+    else if (strcmp(key, "alternate-scroll-mode") == 0)
+        conf->mouse.alternate_scroll_mode = str_to_bool(value);
+
     else {
         LOG_AND_NOTIFY_ERR("%s:%d: [mouse]: %s: invalid key", path, lineno, key);
         return false;
@@ -1907,6 +1910,7 @@ config_load(struct config *conf, const char *conf_path,
         },
         .mouse = {
             .hide_when_typing = false,
+            .alternate_scroll_mode = true,
         },
         .csd = {
             .preferred = CONF_CSD_PREFER_SERVER,

config.h

@@ -119,6 +119,7 @@ struct config {
 
     struct {
         bool hide_when_typing;
+        bool alternate_scroll_mode;
     } mouse;
 
     struct {

doc/foot.ini.5.scd

@@ -143,6 +143,24 @@ applications can change these at runtime.
 *hide-when-typing*
 	Boolean. When enabled, the mouse cursor is hidden while typing.
 
+*alternate-scroll-mode*
+	Boolean. This option controls the initial value for the _alternate
+	scroll mode_. When this mode is enabled, mouse scroll events are
+	translated to _up_/_down_ key events when displaying the alternate
+	screen.
+	
+	This lets you scroll with the mouse in e.g. pagers (like _less_)
+	without enabling native mouse support in them.
+	
+	Alternate scrolling is *not* used if the application enables
+	native mouse support.
+	
+	This option can be modified by applications at run-time using the
+	escape sequences *CSI ? 1007 h* (enable) and *CSI ? 1007 l`
+	(disable).
+	
+	Default: _yes_.
+
 
 # SECTION: colors
 

foot.ini

@@ -23,6 +23,7 @@
 
 [mouse]
 # hide-when-typing=no
+# alternate-scroll-mode=yes
 
 [colors]
 # alpha=1.0

terminal.c

@@ -964,6 +964,7 @@ term_init(const struct config *conf, struct fdm *fdm, struct reaper *reaper,
         .grid = &term->normal,
         .composed_count = 0,
         .composed = NULL,
+        .alt_scrolling = conf->mouse.alternate_scroll_mode,
         .meta = {
             .esc_prefix = true,
             .eight_bit = true,