feat(arc): add knob offset utility (#3589)

Co-authored-by: tvanfossen <vanfosst@gmail.com>
Co-authored-by: Gabor Kiss-Vamosi <kisvegabor@gmail.com>

docs/widgets/arc.md

@@ -41,6 +41,10 @@ The mode can be set by `lv_arc_set_mode(arc, LV_ARC_MODE_...)` and used only if
 If the arc is pressed the current value will set with a limited speed according to the set *change rate*.
 The change rate is defined in degree/second unit and can be set with `lv_arc_set_change_rage(arc, rate)`
 
+### Knob offset
+Changing the knob offset allows the location of the knob to be moved relative to the end of the arc
+The knob offset can be set by `lv_arc_set_knob_offset(arc, offset_angle)`, will only be visible if LV_PART_KNOB is visible
+
 
 ### Setting the indicator manually
 It's also possible to set the angles of the indicator arc directly with `lv_arc_set_angles(arc, start_angle, end_angle)` function or `lv_arc_set_start/end_angle(arc, start_angle)`.

src/widgets/arc/lv_arc.c

@@ -266,6 +266,14 @@ void lv_arc_set_change_rate(lv_obj_t * obj, uint16_t rate)
     arc->chg_rate = rate;
 }
 
+void lv_arc_set_knob_offset(lv_obj_t * obj, int16_t offset)
+{
+    LV_ASSERT_OBJ(obj, MY_CLASS);
+    lv_arc_t * arc = (lv_arc_t *)obj;
+
+    arc->knob_offset = offset;
+}
+
 /*=====================
  * Getter functions
  *====================*/
@@ -324,6 +332,12 @@ int16_t lv_arc_get_rotation(const lv_obj_t * obj)
     return ((lv_arc_t *)obj)->rotation;
 }
 
+int16_t lv_arc_get_knob_offset(const lv_obj_t * obj)
+{
+    LV_ASSERT_OBJ(obj, MY_CLASS);
+    return ((lv_arc_t *)obj)->knob_offset;
+}
+
 /*=====================
  * Other functions
  *====================*/
@@ -785,8 +799,9 @@ static void get_knob_area(lv_obj_t * obj, const lv_point_t * center, lv_coord_t
     r -= indic_width_half;
 
     lv_coord_t angle = get_angle(obj);
-    lv_coord_t knob_x = (r * lv_trigo_sin(angle + 90)) >> LV_TRIGO_SHIFT;
+    lv_coord_t knob_offset = lv_arc_get_knob_offset(obj);
-    lv_coord_t knob_y = (r * lv_trigo_sin(angle)) >> LV_TRIGO_SHIFT;
+    lv_coord_t knob_x = (r * lv_trigo_sin(knob_offset + angle + 90)) >> LV_TRIGO_SHIFT;
+    lv_coord_t knob_y = (r * lv_trigo_sin(knob_offset + angle)) >> LV_TRIGO_SHIFT;
 
     lv_coord_t left_knob = lv_obj_get_style_pad_left(obj, LV_PART_KNOB);
     lv_coord_t right_knob = lv_obj_get_style_pad_right(obj, LV_PART_KNOB);

src/widgets/arc/lv_arc.h

@@ -50,6 +50,7 @@ typedef struct {
     uint16_t chg_rate;          /*Drag angle rate of change of the arc (degrees/sec)*/
     uint32_t last_tick;         /*Last dragging event timestamp of the arc*/
     int16_t last_angle;         /*Last dragging angle of the arc*/
+    int16_t knob_offset;        /*knob offset from the main arc*/
 } lv_arc_t;
 
 extern const lv_obj_class_t lv_arc_class;
@@ -163,6 +164,13 @@ void lv_arc_set_range(lv_obj_t * obj, int16_t min, int16_t max);
  */
 void lv_arc_set_change_rate(lv_obj_t * obj, uint16_t rate);
 
+/**
+ * Set an offset for the knob from the main arc object
+ * @param arc       pointer to an arc object
+ * @param offset    knob offset from main arc
+ */
+void lv_arc_set_knob_offset(lv_obj_t * arc, int16_t offset);
+
 /*=====================
  * Getter functions
  *====================*/
@@ -230,6 +238,13 @@ lv_arc_mode_t lv_arc_get_mode(const lv_obj_t * obj);
  */
 int16_t lv_arc_get_rotation(const lv_obj_t * obj);
 
+/**
+ * Get the current knob offset
+ * @param arc       pointer to an arc object
+ * @return          arc's current knob offset
+ */
+int16_t lv_arc_get_knob_offset(const lv_obj_t * obj);
+
 /*=====================
  * Other functions
  *====================*/