[FFmpeg-devel] [PATCH v2] avcodec/libjxlenc: support negative linesizes

[James Almer]

On 1/30/2024 12:06 PM, Leo Izen wrote:
> On 1/30/24 09:57, Andreas Rheinhardt wrote:
>>
>> Please don't rely on the type of jxl_fmt.align here (which is out of our
>> control). E.g. in the future it may be that libjxl supports only 32bit
>> align values (i.e. uses uint32_t or so for it), but that we support
>> 64bit (ptrdiff_t) linesizes and allocations, so that jxl_fmt.align *
>> (info.ysize - 1) may overflow this even when -linesize fits into
>> jxl_fmt.align.
>> (Very unlikely given that align is size_t and they will likely not go
>> back from this, but it could happen.)
>>
> 
> This would be an ABI break though, wouldn't it? Why do we need to work 
> around a potential future ABI break?

Point is, we have control over frame->linesize[0], but not over 
jxl_fmt.align, so the former is better to calculate offsets in our code.