[FFmpeg-devel] [PATCH 1/2 v2] avutil: add a Tile Grid API

[Anton Khirnov]

Quoting James Almer (2024-01-21 18:47:43)
> On 1/21/2024 2:29 PM, Anton Khirnov wrote:
> > Honestly this whole new API strikes me as massively overthinking it. All
> > you should need to describe an arbitrary partition of an image into
> > sub-rectangles is an array of (x, y, width, height). Instead you're
> > proposing a new public header, struct, three functions, multiple "tile
> > types", and if I'm not mistaken it still cannot describe an arbitrary
> > partitioning. Plus it's in libavutil for some reason, even though
> > libavformat seems to be the only intended user.
> > 
> > Is all this complexity really warranted?
> 
> 1. It needs to be usable as a Stream Group type, so a struct is 
> required. Said struct needs an allocator unless we want to have its size 
> be part of the ABI. I can remove the free function, but then the caller 
> needs to manually free any internal data.

If the struct lives in lavf and is always allocated as a part of
AVStreamGroup then you don't need a public constructor/destructor and
can still extend the struct.

> 2. We need tile dimensions (Width and height) plus row and column count, 
> which give you the final size of the grid, then offsets x and y to get 
> the actual image within the grid meant for presentation.
> 3. I want to support uniform tiles as well as variable tile dimensions, 
> hence multiple tile types. The latter currently has no use case, but 
> eventually might. I can if you prefer not include said type at first, 
> but i want to keep the union in place so it and other extensions can be 
> added.
> 4. It's in lavu because its meant to be generic. It can also be used to 
> transport tiling and cropping information as stream and packet side 
> data, which can't depend on something defined in lavf.

When would you have tiling information associated with a specific
stream?

> And what do you mean with not supporting describing arbitrary 
> partitioning? Isn't that what variable tile dimensions achieve?

IIUC your tiling scheme still assumes that the partitioning is by rows
and columns. A completely generic partitioning could be irregular.

-- 
Anton Khirnov