How to get monitor physical size in millimeters(mm) or centimetre(cm)?

[luozhonghe]

I know that egui::Ui provides the .native_pixels_per_point(), .pixels_per_point(), and .zoom_factor() methods, but how can we know exactly how to set pixels_per_point if we don't know the physical size of the monitor(in millimeters)? A 24-inch 4K monitor and a 32-inch 4K monitor will definitely require different settings, right?

[luozhonghe]

I found a solution that allows me to query the physical dimensions of a monitor using the piaf library.

https://docs.rs/piaf/latest/piaf/struct.DisplayCapabilities.html

Code Example:

[dependencies]
piaf = "0.4"

fn parse_display_capabilities(edid_bytes: &[u8]) -> Result<piaf::DisplayCapabilities, piaf::model::diagnostics::EdidError> {
    let library = piaf::ExtensionLibrary::with_standard_handlers();
    let parsed = piaf::parse_edid(&edid_bytes, &library)?;
    Ok(piaf::capabilities_from_edid(&parsed, &library))
}

fn main() -> Result<(), Box<dyn std::error::Error>> {
    // "/sys/class/drm/card0-HDMI-A-1/edid"
    // "/sys/class/drm/card1-HDMI-A-1/edid"
    let path = "/sys/class/drm/card1-HDMI-A-1/edid";
    let edid_bytes = std::fs::read(path)?;

    let caps = parse_display_capabilities(&edid_bytes)?;
    // println!("{:?}", caps);

    if let Some(val) = caps.manufacturer {
        println!("manufacturer: {:?}", val.as_str());
    }
    if let Some(val) = caps.manufacture_date {
        println!("manufacture_date: {:?}", val);
    }
    if let Some(val) = caps.display_name {
        println!("display_name: {:?}", val.as_str());
    }
    if let Some(val) = caps.serial_number_string {
        println!("serial_number_string: {:?}", val);
    }

    if let Some(val) = caps.screen_size {
        // in centimetre(cm)
        println!("screen_size: {:?}", val);
    }
    if let Some(val) = caps.max_pixel_clock_mhz {
        println!("max_pixel_clock_mhz: {:?}", val);
    }

    Ok(())
}