lvgl/docs/widgets/extra/meter.md

```eval_rst
.. include:: /header.rst 
:github_url: |github_link_base|/widgets/extra/meter.md
```
# Meter (lv_meter)

## Overview
The Meter widget can visualize data in very flexible ways. In can show arcs, needles, ticks lines and labels.

## Parts and Styles
- `LV_PART_MAIN` The background of the Meter. Uses the typical background properties. 
- `LV_PART_TICK` The tick lines a labels using the *line* and *text* style properties.
- `LV_PART_INDICATOR` The needle line or image using the *line* and *img* style properties, as well as the background properties to draw a square (or circle) on the pivot of the needles. Padding makes the square larger.
- `LV_PART_ITEMS` The arcs using the *arc* properties.

## Usage

### Add a scale

First a *Scale* needs to be added to the Meter with `lv_meter_scale_t * scale = lv_meter_add_scale(meter)`. 
The Scale has minor and major ticks and labels on the major ticks. Later indicators (needles, arcs, tick modifiers) can be added to the meter

Any number of scales can be added to Meter.

The minor tick lines can be configured with: `lv_meter_set_scale_ticks(meter, scale, tick_count, line_width, tick_length, ctick_olor)`.

To add major tick lines use `lv_meter_set_scale_major_ticks(meter, scale, nth_major, tick_width, tick_length, tick_color, label_gap)`. `nth_major` to specify how many minor ticks to skip to draw a major tick.

Labels are added automatically on major ticks with `label_gap` distance from the ticks with text proportionally to the values of the tick line.

`lv_meter_set_scale_range(meter, scale, min, max, angle_range, rotation)` sets the value and angle range of the scale.

### Add indicators

Indicators need to be added to a Scale and their value is interpreted in the range of the Scale.

All the indicator add functions return `lv_meter_indicator_t *`.

#### Needle line

`indic = lv_meter_add_needle_line(meter, scale, line_width, line_color, r_mod)` adds a needle line to a Scale. By default, the length of the line is the same as the scale's radius but `r_mod` changes the length.

`lv_meter_set_indicator_value(meter, indic, value)` sets the value of the indicator.

#### Needle image

`indic = lv_meter_add_needle_img(meter, scale, img_src, pivot_x, pivot_y)` sets an image that will be used as a needle. `img_src` should be a needle pointing to the right like this `-O--->`.
`pivot_x` and `pivot_y` sets the pivot point of the rotation relative to the top left corner of the image. 

`lv_meter_set_indicator_value(meter, inidicator, value)` sets the value of the indicator.

#### Arc
`indic = lv_meter_add_arc(meter, scale, arc_width, arc_color, r_mod)` adds and arc indicator. . By default, the radius of the arc is the same as the scale's radius but `r_mod` changes the radius.

`lv_meter_set_indicator_start_value(meter, indic, value)` and `lv_meter_set_indicator_end_value(meter, inidicator, value)` sets the value of the indicator. 

#### Scale lines (ticks)
`indic = lv_meter_add_scale_lines(meter, scale, color_start, color_end, local, width_mod)` adds an indicator that modifies the ticks lines. 
If `local` is `true` the ticks' color will be faded from `color_start` to `color_end` in the indicator's  start and end value range. 
If `local` is `false` `color_start` and `color_end` will be mapped to the start and end value of the scale and only a "slice" of that color gradient will be visible in the indicator's start and end value range.
`width_mod` modifies the width of the tick lines.

`lv_meter_set_indicator_start_value(meter, inidicator, value)` and `lv_meter_set_indicator_end_value(meter, inidicator, value)` sets the value of the indicator. 

## Events
- `LV_EVENT_DRAW_PART_BEGIN` and `LV_EVENT_DRAW_PART_END` is sent for the following types:
    - `LV_METER_DRAW_PART_ARC` The arc indicator
       - `part`: `LV_PART_ITEMS`
       - `sub_part_ptr`: pointer to the indicator
       - `arc_dsc`
       - `radius`: radius of the arc
       - `p1` center of the arc
    - `LV_METER_DRAW_PART_NEEDLE_LINE` The needle lines
       - `part`: `LV_PART_ITEMS`
       - `p1`, `p2` points of the line
       - `line_dsc`
       - `sub_part_ptr`: pointer to the indicator
    - `LV_METER_DRAW_PART_NEEDLE_IMG`  The needle images
       - `part`: `LV_PART_ITEMS`
       - `p1`, `p2` points of the line
       - `img_dsc`
       - `sub_part_ptr`: pointer to the indicator
    - `LV_METER_DRAW_PART_TICK` The tick lines and labels
       - `part`: `LV_PART_TICKS`
       - `value`: the value of the line
       - `text`: `value` converted to decimal or `NULL` on minor lines
       - `label_dsc`: label draw descriptor or `NULL` on minor lines
       - `line_dsc`: 
       - `id`: the index of the line      
    
    
See the events of the [Base object](/widgets/obj) too.
    
Learn more about [Events](/overview/event).

## Keys
No keys are handled by the Meter widget.

Learn more about [Keys](/overview/indev).


## Example

```eval_rst

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

```

## API 

```eval_rst

.. doxygenfile:: lv_meter.h
  :project: lvgl
        
```