Function decode_frame

rustcv-camera/src/decode.rs:36–86

Decode a [`Frame`] into a BGR [`Mat`]. 将 [`Frame`] 解码为 BGR [`Mat`]。 The `decompressor` parameter is for reusing a turbojpeg Decompressor across frames (avoiding per-frame allocation). Pass `None` to create a temporary one. `decompressor` 参数用于跨帧复用 turbojpeg Decompressor （避免每帧分配）。传入 `None` 则创建临时的。

(
    frame: &Frame<'_>,
    mat: &mut Mat,
    #[cfg(feature = "turbojpeg")] _decompressor: Option<&mut turbojpeg::Decompressor>,
    #[cfg(not(feature = "turbojpeg"))] _decompressor: Option<()>,
)

/// `decompressor` 参数用于跨帧复用 turbojpeg Decompressor
/// （避免每帧分配）。传入 `None` 则创建临时的。
pub fn decode_frame(
    frame: &Frame<'_>,
    mat: &mut Mat,
    #[cfg(feature = "turbojpeg")] _decompressor: Option<&mut turbojpeg::Decompressor>,
    #[cfg(not(feature = "turbojpeg"))] _decompressor: Option<()>,
) -> Result<()> {
    let w = frame.width();
    let h = frame.height();

    match frame.pixel_format() {
        PixelFormat::Mjpeg => {
            mat.ensure_size(h, w, 3);
            decode_mjpeg(frame.data(), mat)?;
        }
        PixelFormat::Yuyv => {
            mat.ensure_size(h, w, 3);
            yuyv_to_bgr(frame.data(), mat.data_mut(), w as usize, h as usize);
        }
        PixelFormat::Bgr24 => {
            // Already BGR — just copy.
            // 已经是 BGR —— 直接拷贝。
            mat.ensure_size(h, w, 3);
            let expected = (w * h * 3) as usize;
            if frame.data().len() >= expected {
                mat.data_mut()[..expected].copy_from_slice(&frame.data()[..expected]);
            }
        }
        PixelFormat::Rgb24 => {
            // RGB → BGR: swap R and B channels.
            // RGB → BGR：交换 R 和 B 通道。
            mat.ensure_size(h, w, 3);
            rgb_to_bgr(frame.data(), mat.data_mut());
        }
        PixelFormat::Bgra32 => {
            // BGRA32 → BGR24: drop the alpha channel.
            // macOS AVFoundation native format (kCVPixelFormatType_32BGRA).
            // BGRA32 → BGR24：去掉 Alpha 通道。
            // macOS AVFoundation 原生格式（kCVPixelFormatType_32BGRA）。
            mat.ensure_size(h, w, 3);
            bgra32_to_bgr(frame.data(), mat.data_mut());
        }
        other => {
            return Err(CameraError::DecodeError(format!(
                "unsupported pixel format for decode: {:?}",
                other
            )));
        }
    }

    Ok(())
}

// ─── MJPEG decode ───────────────────────────────────────────────────────────