add more info to detect double clicks

inc/ztoolkit/ztk_widget.h

@@ -207,19 +207,30 @@ typedef struct ZtkWidget
 
   /**
    * Last time a press was finished.
+   */
+  double            last_btn_release;
+
+  /**
+   * Last time a press was finished, before
+   * the latest one.
    *
    * This is used to detect double clicks.
    */
-  double            last_btn_release;
+  double            before_last_btn_release;
 
   /**
    * Last time a button was held down.
-   *
-   * If this minus \ref ZtkWidget.last_btn_release
-   * is short enough, this is a double click.
    */
   double            last_btn_press;
 
+  /**
+   * Last time a button was held down,
+   * before the latest one.
+   *
+   * This is used to detect double clicks.
+   */
+  double            before_last_btn_press;
+
   /** Cairo caches. */
   cairo_t *         cached_cr;
   cairo_surface_t * cached_surface;

src/ztk_app.c

@@ -182,6 +182,7 @@ post_event_to_widgets (
                 is_first_widget_hit (
                   self, w, ev->x, ev->y))
               {
+                w->before_last_btn_press = w->last_btn_press;
                 w->last_btn_press = ev->time;
                 w->state |=
                   ZTK_WIDGET_STATE_PRESSED;
@@ -211,6 +212,7 @@ post_event_to_widgets (
             w->state &=
               (unsigned int)
               ~ZTK_WIDGET_STATE_PRESSED;
+            w->before_last_btn_release = w->last_btn_release;
             w->last_btn_release = ev->time;
             if (w->visible &&
                 w->button_event_cb &&