df_ddc

DDC/CI (VESA MCCS) monitor control backend. Low-level I/O layer for VCP features: brightness, contrast, volume, input, power.

Backends

On Linux, buses that do not answer a standard VCP probe are skipped, which filters out notebook-internal smbus devices.

Usage

use df_ddc::list_monitors;

fn main() -> Result<(), Box<dyn std::error::Error>> {
    for (i, dev) in list_monitors().iter().enumerate() {
        let caps = dev.inner.get_capabilities()?;
        println!("[{i}] {}  bright={}/{}  contrast={}/{}",
            dev.info, caps.brightness, caps.brightness_max,
            caps.contrast, caps.contrast_max);

        dev.inner.set_brightness(50)?;
    }
    Ok(())
}

API

• list_monitors() -> Vec<DisplayDevice> — enumerate DDC-capable monitors.
• DisplayDevice::info: String — OS-supplied description (e.g. \\.\DISPLAY1\Monitor0 or I2C Display Bus (i2c-4)).
• trait DdcControl (ddc_trait.rs):
  • get_capabilities() -> Result<MonitorCapabilities, DdcError>
  • get_vcp_feature(code: u8) -> Result<VcpValue, DdcError>
  • set_vcp_feature(code: u8, value: u16) -> Result<(), DdcError>
  • set_brightness(value: u32)
  • set_contrast(value: u32)
  • set_power(state: PowerState)
  • set_input(source: InputSource)
• Types (ddc_types.rs): MonitorCapabilities, InputSource, PowerState, VcpCode, VcpValue.

Bundled binary

src/bin/ddc_mgr.rs — small standalone CLI for smoke tests:

cargo run -p df_ddc --bin ddc_mgr -- --help

Benchmarks

cargo bench -p df_ddc

benches/ddc_operations.rs uses criterion.

Platform gates

• cfg(target_os = "windows") — pulls windows crate with Win32_Graphics_Gdi and Win32_Devices_Display.
• cfg(target_os = "linux") — pulls libc for I2C ioctl.

Safety notes

• The Windows callback in list_monitors() is unsafe extern "system". The vector must outlive the call to EnumDisplayMonitors; this is guaranteed by the call structure.
• On Linux, each I2C bus is briefly open()/ioctl()-probed. Measured at well under 50 ms for a single-thread enumeration.

License

MIT OR Apache-2.0