Method open

rustcv-camera/src/backend/macos/mod.rs:121–183

Open the camera device at `index` (embedded in the `device` string). 打开 `device` 字符串中 `index` 指定的摄像头设备。

(&mut self, device: &str, config: &CameraConfig)

    /// Open the camera device at `index` (embedded in the `device` string).
    /// 打开 `device` 字符串中 `index` 指定的摄像头设备。
    pub fn open(&mut self, device: &str, config: &CameraConfig) -> Result<ResolvedConfig> {
        // On macOS the "device path" is just the numeric index as a string.
        // 在 macOS 上，"设备路径"只是数字索引的字符串形式。
        let index: c_uint = device.parse().unwrap_or(0);
        let width = config.width.unwrap_or(640) as c_uint;
        let height = config.height.unwrap_or(480) as c_uint;
        let fps = config.fps.unwrap_or(30) as c_uint;

        let mut actual_w: c_uint = width;
        let mut actual_h: c_uint = height;
        let mut cam_ptr: *mut sys::AvfCameraOpaque = std::ptr::null_mut();

        let ret = unsafe {
            sys::avf_camera_open(
                index,
                width,
                height,
                fps,
                &mut actual_w,
                &mut actual_h,
                &mut cam_ptr,
            )
        };

        match ret {
            AVF_OK => {}
            AVF_ERR_PERMISSION => {
                return Err(CameraError::DeviceNotFound(
                    "camera access denied — allow camera in System Settings > Privacy".to_string(),
                ));
            }
            AVF_ERR_DEVICE_NOT_FOUND => {
                return Err(CameraError::DeviceNotFound(format!(
                    "no camera at index {}",
                    index
                )));
            }
            code => {
                return Err(CameraError::DeviceNotFound(format!(
                    "AVFoundation session error (code {})",
                    code
                )));
            }
        }

        self.cam = cam_ptr;

        // Pre-allocate the frame buffer for the requested resolution (BGRA32).
        // The bridge (bridge.m) guarantees frames are delivered at exactly
        // (actual_w × actual_h) via vImage scaling, so no headroom is needed.
        // 按请求分辨率预分配帧缓冲区（BGRA32）。
        // bridge 通过 vImage 缩放保证每帧都以 (actual_w × actual_h) 交付，
        // 无需额外预留空间。
        self.frame_buf.resize((actual_w * actual_h * 4) as usize, 0);

        Ok(ResolvedConfig {
            width: actual_w,
            height: actual_h,