lvgl/docs/widgets/core/arc.md

.. include:: /header.rst 
:github_url: |github_link_base|/widgets/arc.md

Arc (lv_arc)

Overview

The Arc are consists of a background and a foreground arc. The foregrond (indicator) arc can be adjusted by finger.

Parts and Styles

• LV_PART_MAIN It draws a background using the typical background style properties and an arc using the arc style properties. The arc's size and position will respect the padding style properties.
• LV_PART_INDICATOR It draws an other arc using the arc style properties. It's padding values are interpreted relative to the background arc.
• LV_PART_KNOBIt draws a handle on the end of the indicator. It uses all background properties and padding values. With zero padding the knob size is the same as the indicator's width. Larger padding makes it larger, smaller padding makes it smaller.

Usage

Value and range

A new value can be set by lv_arc_set_value(arc, new_value). The value is interpreted in a range (minimum and maximum values) which can be modified with lv_arc_set_range(arc, min, max). The default range is 1..100.

The indicator arc is drawn on the main part's arc. That is if the vale is set to maximum the indicator arc will cover the entire "background" arc. To set the start and end angl of the background arc use the lv_arc_set_bg_angles(arc, start_angle, end_angle) function or lv_arc_set_bg_start/end_angle(arc, start_angle).

Zero degree is at the middle right (3 o'clock) of the object and the degrees are increasing in clockwise direction. The angles should be in [0;360] range.

Rotation

An offset to the 0 degree position can added with lv_arc_set_rotation(arc, deg).

Mode

The arc can be one of the following modes:

• LV_ARC_MODE_NORMAL The indicator arc is drawn from the minimimum value to the current.
• LV_ARC_MODE_REVERSE The indicator arc is drawn counter clockwise from the maximum value to the current.
• LV_ARC_MODE_SYMMETRICAL The indicator arc is drawn from the middle point to the current value.

The mode can be set by lv_arc_set_mode(arc, LV_ARC_MODE_...) and used only if the the angle is set by lv_arc_set_value() or the arc is adjusted by finger.

Change rate

If the 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)

Setting the indicator manually

It also possible to set the angles o 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) sets the angles of the indicator arc. In this case the set "value" and "mode" is ignored.

In other words, settings angles and values are independent. You should use either value and angle settings. Mixing the two might result unintended behavior.

To make the arc non-adjutabe remove the style of the knob and make the object non-clickable:

lv_obj_remove_style(arc, NULL, LV_PART_KNOB);
lv_obj_clear_flag(arc, LV_OBJ_FLAG_CLICKABLE);

Events

• LV_EVENT_VALUE_CHANGED sent when the arc is pressed/dragged to set a new value.
• LV_EVENT_DRAW_PART_BEGIN and LV_EVENT_DRAW_PART_END are sent for the background rectangle, the background arc, the foreground arc and the knob to allow hooking the drawing. For more detail on the backround rectangle part see the Base object's documentation. The fields of lv_obj_draw_dsc_t is set like the followings:
  • For both arcs: clip_area, p1 (center of the arc), radius, arc_dsc, part.
  • For the knob: clip_area, draw_area, rect_dsc, part.

Learn more about Events.

Keys

• LV_KEY_RIGHT/UP Increases the value by one.
• LV_KEY_LEFT/DOWN Decreases the value by one.

Learn more about Keys.

Example

.. include:: ../../../examples/widgets/arc/index.rst

API

.. doxygenfile:: lv_arc.h
  :project: lvgl