0x8040 · brightnessControl

设备背光亮度控制——读取支持的亮度范围与步数、读写当前亮度值，并可独立开关背光照明。

控制设备的显示屏或背光亮度。getInfo（function 0）返回一个 BrightnessInfo，其中包含最小/最大亮度、离散步数以及 BrightnessCapabilities 位掩码。getBrightness / setBrightness（functions 1–2）以 u16 格式读取和写入当前亮度值。当 ILLUMINATION 能力标志被置位时，getIllumination / setIllumination（functions 3–4）可在不改变已存储亮度值的情况下，独立查询和切换背光的开关状态。

HARDWARE_BRIGHTNESS —— 硬件可在无需主机命令的情况下自行调节亮度。
EVENTS —— 设备会主动上报亮度或背光状态变更事件。
ILLUMINATION —— 背光开关状态可独立于亮度值进行查询与控制。
HARDWARE_ON_OFF —— 硬件可直接切换背光的开/关状态。
TRANSIENT —— 亮度值不会在设备断电后持久化。

规格： Logitech HID++ 2.0 —— brightnessControl。用于： openlogi-hidpp 中的类型化封装。

Function reference

The BrightnessControlFeature wrapper (0x8040) exposes:

Methods

Function	HID++ fn	Signature	Returns
`get_info`	0	`()`	`BrightnessInfo`
`get_brightness`	1	`()`	`u16`
`set_brightness`	2	`(brightness: u16)`	`()`
`get_illumination`	3	`()`	`bool`
`set_illumination`	4	`(enabled: bool)`	`()`

All methods are async and return Result<…, Hidpp20Error>.

Types

`BrightnessInfo`

Brightness range and capability information.

Field	Type	Description
`min_brightness`	`u16`	Minimum accepted brightness.
`max_brightness`	`u16`	Maximum accepted brightness.
`steps`	`u16`	Number of brightness steps advertised by the device.
`capabilities`	`BrightnessCapabilities`	Feature capabilities.

`BrightnessCapabilities`

Capabilities reported by BrightnessControl.

Flag	Bit/Value	Description
`HARDWARE_BRIGHTNESS`	`1 << 0`	Hardware can change brightness directly.
`EVENTS`	`1 << 1`	The device emits brightness or illumination change events.
`ILLUMINATION`	`1 << 2`	Illumination can be queried and controlled separately from brightness.
`HARDWARE_ON_OFF`	`1 << 3`	Hardware can toggle illumination on and off directly.
`TRANSIENT`	`1 << 4`	Brightness is transient and not persisted by the device.

Wire format

Short requests carry a 3-byte payload; getInfo / getBrightness / getIllumination responses are read from the 16-byte extended payload returned by extend_payload().

`get_info` (fn 0)

Request: [0x00, 0x00, 0x00]

Response (extended 16-byte payload — byte → field):

Byte(s)	Field	Notes
0–1	`max_brightness`	Big-endian `u16`.
2	`steps` (low byte)	Combined with byte 6 — see note below.
3	`capabilities`	`BrightnessCapabilities` bitmask (see flag table above).
4–5	`min_brightness`	Big-endian `u16`.
6	`steps` (high byte)	`steps = u16::from_be_bytes([payload[6], payload[2]])`.

The steps field is split across two non-adjacent bytes: high byte at index 6, low byte at index 2.

`get_brightness` (fn 1)

Request: [0x00, 0x00, 0x00]

Response (extended 16-byte payload — byte → field):

Byte(s)	Field	Notes
0–1	brightness	Big-endian `u16` current brightness value.

`set_brightness` (fn 2)

Request: [hi, lo, 0x00] where hi and lo are the big-endian bytes of the u16 brightness value.

Byte	Content
0	`(brightness >> 8) as u8`
1	`brightness as u8`
2	`0x00` (padding)

No response payload is used.

`get_illumination` (fn 3)

Request: [0x00, 0x00, 0x00]

Response (extended 16-byte payload — byte → field):

Byte	Field	Notes
0	illumination enabled	Bit 0: `payload[0] & 1 != 0`. `true` = illumination on.

`set_illumination` (fn 4)

Request: [enabled, 0x00, 0x00]

Byte	Content
0	`0x01` if illumination should be enabled, `0x00` to disable
1–2	`0x00` (padding)

No response payload is used.

Usage (Rust)

use hidpp::{device::Device, feature::brightness_control::BrightnessControlFeature};

// mut device: Device, already created via Device::new(channel, index)?
device.enumerate_features().await?;
if let Some(feat) = device.get_feature::<BrightnessControlFeature>() {
    let info = feat.get_info().await?;
    println!("Brightness range: {}–{} ({} steps)", info.min_brightness, info.max_brightness, info.steps);

    let current = feat.get_brightness().await?;
    println!("Current brightness: {current}");

    // Set brightness to 75 % of the reported maximum
    let target = (info.max_brightness as u32 * 75 / 100) as u16;
    feat.set_brightness(target).await?;

    if info.capabilities.contains(hidpp::feature::brightness_control::BrightnessCapabilities::ILLUMINATION) {
        let on = feat.get_illumination().await?;
        println!("Illumination currently: {on}");
        feat.set_illumination(true).await?;
    }
}

0x8040 · brightnessControl

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