feat(scroll): add lv_obj_update_snap()

src/lv_core/lv_indev_scroll.c

@@ -230,6 +230,12 @@ lv_coord_t lv_indev_scroll_throw_predict(lv_indev_t * indev, lv_dir_t dir)
     return sum;
 }
 
+void lv_indev_scroll_get_snap_dist(lv_obj_t * obj, lv_point_t * p)
+{
+    p->x = find_snap_point_x(obj, obj->coords.x1, obj->coords.x2, 0);
+    p->y = find_snap_point_y(obj, obj->coords.y1, obj->coords.y2, 0);
+}
+
 /**********************
  *   STATIC FUNCTIONS
  **********************/
@@ -398,6 +404,15 @@ static void init_scroll_limits(lv_indev_proc_t * proc)
     if(proc->types.pointer.scroll_area.y2 == 0) proc->types.pointer.scroll_area.y2 = LV_COORD_MAX;
 }
 
+/**
+ * Search for snap point in the `min` - `max` range.
+ * @param obj the object on which snap point should be found
+ * @param min ignore snap points smaller then this. (Absolute coordinate)
+ * @param max ignore snap points greater then this. (Absolute coordinate)
+ * @param ofs offset to snap points. Useful the get a snap point in an imagined case
+ *            what if children are already moved by this value
+ * @return the distance of the snap point.
+ */
 static lv_coord_t find_snap_point_x(const lv_obj_t * obj, lv_coord_t min, lv_coord_t max, lv_coord_t ofs)
 {
     lv_snap_align_t align = lv_obj_get_scroll_snap_align_x(obj);

src/lv_core/lv_indev_scroll.h

@@ -29,24 +29,31 @@ extern "C" {
 
 /**
  * Handle scrolling. Called by LVGL during input device processing
- * @param proc pointer to an input device's proc field
+ * @param proc      pointer to an input device's proc field
  */
 void _lv_indev_scroll_handler(lv_indev_proc_t * proc);
 
 /**
  * Handle throwing after scrolling. Called by LVGL during input device processing
- * @param proc pointer to an input device's proc field
+ * @param proc      pointer to an input device's proc field
  */
 void _lv_indev_scroll_throw_handler(lv_indev_proc_t * proc);
 
 /**
  * Predict where would a scroll throw end
- * @param indev pointer to an input device
- * @param dir `LV_DIR_VER` or `LV_DIR_HOR`
- * @return the difference compared to the current position when the throw would be finished
+ * @param indev     pointer to an input device
+ * @param dir `     LV_DIR_VER` or `LV_DIR_HOR`
+ * @return          the difference compared to the current position when the throw would be finished
  */
 lv_coord_t lv_indev_scroll_throw_predict(lv_indev_t * indev, lv_dir_t dir);
 
+/**
+ * Get the distance of the nearest snap point
+ * @param obj       the object on which snap points should be found
+ * @param p         save the distance of the found snap point there
+ */
+void lv_indev_scroll_get_snap_dist(lv_obj_t * obj, lv_point_t * p);
+
 /**********************
  *      MACROS
  **********************/

src/lv_core/lv_obj_scroll.c

@@ -10,6 +10,7 @@
 #include "lv_obj.h"
 #include "lv_indev.h"
 #include "lv_disp.h"
+#include "lv_indev_scroll.h"
 
 /*********************
  *      DEFINES
@@ -396,6 +397,13 @@ void lv_obj_scroll_to_view_recursive(lv_obj_t * obj, lv_anim_enable_t anim_en)
     }
 }
 
+void lv_obj_update_snap(lv_obj_t * obj, lv_anim_enable_t anim_en)
+{
+    lv_point_t p;
+    lv_indev_scroll_get_snap_dist(obj, &p);
+    lv_obj_scroll_by(obj, p.x, p.y, anim_en);
+}
+
 void lv_obj_get_scrollbar_area(lv_obj_t * obj, lv_area_t * hor_area, lv_area_t * ver_area)
 {
     lv_area_set(hor_area, 0, 0, 0, 0);

src/lv_core/lv_obj_scroll.h

@@ -248,6 +248,12 @@ void lv_obj_scroll_to_view(struct _lv_obj_t * obj, lv_anim_enable_t anim_en);
  */
 void lv_obj_scroll_to_view_recursive(struct _lv_obj_t * obj, lv_anim_enable_t anim_en);
 
+/**
+ * Check the children of `obj` and scroll `obj` to fulfill the scroll_snap settings
+ * @param obj       an object whose children needs to checked and snapped
+ * @param anim_en   LV_ANIM_ON/OFF
+ */
+void lv_obj_update_snap(struct _lv_obj_t * obj, lv_anim_enable_t anim_en);
 
 /**
  * Get the area of the scrollbars