evdev-touchpad: Set some options using weston.ini

This patch adds 3 new options to weston.ini to allow
the user to change default constant_accel_factor,
min_accel_factor and max_accel_factor. If no options
are set, it falls back using defaults as it did before.

v2: create weston_config_section_get_double and use it
instead of manualy converting string to double.

v3: add default values in weston_config_get_double
instead of using conditionals.

v4: don't pass diagonal as pointer.

shared/config-parser.c

@@ -335,6 +335,32 @@ weston_config_section_get_uint(struct weston_config_section *section,
 	return 0;
 }
 
+WL_EXPORT
+int
+weston_config_section_get_double(struct weston_config_section *section,
+				 const char *key,
+				 double *value, double default_value)
+{
+	struct weston_config_entry *entry;
+	char *end;
+
+	entry = config_section_get_entry(section, key);
+	if (entry == NULL) {
+		*value = default_value;
+		errno = ENOENT;
+		return -1;
+	}
+
+	*value = strtod(entry->value, &end);
+	if (*end != '\0') {
+		*value = default_value;
+		errno = EINVAL;
+		return -1;
+	}
+
+	return 0;
+}
+
 WL_EXPORT
 int
 weston_config_section_get_string(struct weston_config_section *section,

shared/config-parser.h

@@ -88,6 +88,10 @@ weston_config_section_get_uint(struct weston_config_section *section,
 			       const char *key,
 			       uint32_t *value, uint32_t default_value);
 int
+weston_config_section_get_double(struct weston_config_section *section,
+				 const char *key,
+				 double *value, double default_value);
+int
 weston_config_section_get_string(struct weston_config_section *section,
 				 const char *key,
 				 char **value,