config: add scrollback.multiplier option

This option is used to multiply the mouse scroll amount for mouse and
trackpad based scrollback scrolling.

Closes #54.

CHANGELOG.md

@@ -26,6 +26,8 @@
   **pipe-scrollback**, but only pipes the currently selected text, if
   any (https://codeberg.org/dnkl/foot/issues/51).
 * **cursor.hide-when-typing** option to `footrc.
+* **scrollback.multiplier** option to `footrc`
+  (https://codeberg.org/dnkl/foot/issues/54).
 
 
 ### Deprecated

config.c

@@ -439,6 +439,17 @@ parse_section_scrollback(const char *key, const char *value, struct config *conf
         }
     }
 
+    else if (strcmp(key, "multiplier") == 0) {
+        double multiplier;
+        if (!str_to_double(value, &multiplier)) {
+            LOG_AND_NOTIFY_ERR("%s:%d: [scrollback]: multiplier: "
+                               "invalid value: %s", path, lineno, value);
+            return false;
+        }
+
+        conf->scrollback.multiplier = multiplier;
+    }
+
     else {
         LOG_AND_NOTIFY_ERR("%s:%u: [scrollback]: %s: invalid key", path, lineno, key);
         return false;
@@ -1218,6 +1229,7 @@ config_load(struct config *conf, const char *conf_path, bool errors_are_fatal)
                 .format = SCROLLBACK_INDICATOR_FORMAT_TEXT,
                 .text = wcsdup(L""),
             },
+            .multiplier = 1.,
         },
         .colors = {
             .fg = default_foreground,

config.h

@@ -61,6 +61,7 @@ struct config {
 
             wchar_t *text;
         } indicator;
+        double multiplier;
     } scrollback;
 
     struct {

doc/footrc.5.scd

@@ -77,6 +77,10 @@ in this order:
 *lines*
 	Number of scrollback lines. Default: _1000_.
 
+*multiplier*
+	Amount to multiply mouse scrolling with. It is a decimal number,
+	i.e. fractions are allowed. Default: _1.0_.
+
 *indicator-position*
 	Configures the style of the scrollback position indicator. One of
 	*none*, *fixed* or *relative*. *none* disables the indicator

input.c

@@ -1544,7 +1544,8 @@ wl_pointer_axis(void *data, struct wl_pointer *wl_pointer,
      * Without this, very slow scrolling will never actually scroll
      * anything.
      */
-    seat->mouse.axis_aggregated += wl_fixed_to_double(value);
+    seat->mouse.axis_aggregated
+        += seat->wayl->conf->scrollback.multiplier * wl_fixed_to_double(value);
 
     if (fabs(seat->mouse.axis_aggregated) >= 1.) {
         mouse_scroll(seat, round(seat->mouse.axis_aggregated));
@@ -1561,7 +1562,7 @@ wl_pointer_axis_discrete(void *data, struct wl_pointer *wl_pointer,
 
     struct seat *seat = data;
     seat->mouse.have_discrete = true;
-    mouse_scroll(seat, discrete);
+    mouse_scroll(seat, seat->wayl->conf->scrollback.multiplier * discrete);
 }
 
 static void