Function JxlDecoderSetExtraChannelBuffer 

pub unsafe extern "C-unwind" fn JxlDecoderSetExtraChannelBuffer(
    dec: *mut JxlDecoder,
    format: *const JxlPixelFormat,
    buffer: *mut c_void,
    size: usize,
    index: u32,
) -> JxlDecoderStatus

Sets the buffer to write an extra channel to. This can be set when the JxlDecoderStatus::Frame or JxlDecoderStatus::NeedImageOutBuffer event occurs, and applies only for the current frame. The size of the buffer must be at least as large as given by JxlDecoderExtraChannelBufferSize. The buffer follows the format described by JxlPixelFormat, but where num_channels is 1. The buffer is owned by the caller. The amount of extra channels is given by the num_extra_channels field in the associated JxlBasicInfo, and the information of individual extra channels can be queried with JxlDecoderGetExtraChannelInfo. To get multiple extra channels, this function must be called multiple times, once for each wanted index. Not all images have extra channels. The alpha channel is an extra channel and can be gotten as part of the color channels when using an RGBA pixel buffer with JxlDecoderSetImageOutBuffer, but additionally also can be gotten separately as extra channel. The color channels themselves cannot be gotten this way.

Parameters

• dec: decoder object
• format: format of the pixels. Object owned by user and its contents are copied internally. The num_channels value is ignored and is always treated to be 1.
• buffer: buffer type to output the pixel data to
• size: size of buffer in bytes
• index: which extra channel to get, matching the index used in JxlDecoderGetExtraChannelInfo. Must be smaller than num_extra_channels in the associated JxlBasicInfo.

Returns

• JxlDecoderStatus::Success on success, JxlDecoderStatus::Error on error, such as size too small or invalid index.