[Spice-devel] [PATCH spice-streaming-agent] jpeg: Do not use next_output_byte buf_empty_output_buffer

[Uri Lublin]

On 07/17/2018 06:28 PM, Frediano Ziglio wrote:

Hi Frediano,

> The pointer is not updated to the last byte used so using it
> to compute the bytes written into the buffer we ignore some bytes
> causing some image corruptions.
> Note that also free_in_buffer is not updated to last written byte.
> When buf_empty_output_buffer is called the buffer is full so use the
> size of it instead of relaying on next_output_byte or free_in_buffer.

I also found in /usr/share/doc/libjpeg-turbo-devel/libjpeg.txt,
under empty_output_buffer:
  "(use the saved start address and buffer length;
    ignore the current state of next_output_byte and free_in_buffer)."

Some printfs show that sometimes a few bytes are "missing".

I tested this patch and it does fix the problem for me.

typo: s/relaying/relying/

> 
> Signed-off-by: Frediano Ziglio <fziglio at redhat.com>

Acked-by: Uri Lublin <uril at redhat.com>

Thanks,
     Uri.


> ---
>   src/jpeg.cpp | 2 +-
>   1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/src/jpeg.cpp b/src/jpeg.cpp
> index ceee359..5f6d128 100644
> --- a/src/jpeg.cpp
> +++ b/src/jpeg.cpp
> @@ -23,7 +23,7 @@ struct JpegBuffer: public jpeg_destination_mgr
>   static boolean buf_empty_output_buffer(j_compress_ptr cinfo)
>   {
>       JpegBuffer *buf = (JpegBuffer *) cinfo->dest;
> -    size_t size = buf->next_output_byte - &buf->buffer[0];
> +    size_t size = buf->buffer.size();
>       buf->buffer.resize(buf->buffer.capacity() * 2);
>       buf->next_output_byte = &buf->buffer[0] + size;
>       buf->free_in_buffer = buf->buffer.size() - size;
>