[FFmpeg-trac] #7528(avfilter:new): Slice threading for geq causes visual artifacts

[FFmpeg]

#7528: Slice threading for geq causes visual artifacts
-------------------------------------+-------------------------------------
               Reporter:  llogan     |                  Owner:
                   Type:  defect     |                 Status:  new
               Priority:  important  |              Component:  avfilter
                Version:  git-       |               Keywords:  geq
  master                             |  regression
             Blocked By:             |               Blocking:
Reproduced by developer:  0          |  Analyzed by developer:  0
-------------------------------------+-------------------------------------
 ac6b0bba79fe4de1281e0f2058646bee23d90224 causes artifacts in this geq
 example stolen from Gyan:

 {{{
 $ ffmpeg -f lavfi -i nullsrc -vf
 "geq='st(3,pow(X-(W/2),2)+pow(Y-(H/2),2));if(lte(ld(3),pow(min(W/2,H/2),2)),255,0)':128:128"
 -frames:v 1 out.png
 ffmpeg version N-92321-g295fd12d17 Copyright (c) 2000-2018 the FFmpeg
 developers
   built with gcc 8.2.1 (GCC) 20180831
   configuration: --enable-gpl
   libavutil      56. 21.100 / 56. 21.100
   libavcodec     58. 34.100 / 58. 34.100
   libavformat    58. 19.102 / 58. 19.102
   libavdevice    58.  4.107 / 58.  4.107
   libavfilter     7. 39.100 /  7. 39.100
   libswscale      5.  2.100 /  5.  2.100
   libswresample   3.  2.100 /  3.  2.100
   libpostproc    55.  2.100 / 55.  2.100
 Input #0, lavfi, from 'nullsrc':
   Duration: N/A, start: 0.000000, bitrate: N/A
     Stream #0:0: Video: rawvideo (I420 / 0x30323449), yuv420p, 320x240
 [SAR 1:1 DAR 4:3], 25 tbr, 25 tbn, 25 tbc
 Stream mapping:
   Stream #0:0 -> #0:0 (rawvideo (native) -> png (native))
 Press [q] to stop, [?] for help
 Output #0, image2, to 'out.png':
   Metadata:
     encoder         : Lavf58.19.102
     Stream #0:0: Video: png, rgb24, 320x240 [SAR 1:1 DAR 4:3], q=2-31, 200
 kb/s, 25 fps, 25 tbn, 25 tbc
     Metadata:
       encoder         : Lavc58.34.100 png
 frame=    1 fps=0.0 q=-0.0 Lsize=N/A time=00:00:00.04 bitrate=N/A
 speed=2.05x
 video:11kB audio:0kB subtitle:0kB other streams:0kB global headers:0kB
 muxing overhead: unknown
 }}}

 Output looks normal with `-filter_threads 1`/`-filter_complex_threads 1`.

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Ticket URL: <https://trac.ffmpeg.org/ticket/7528>
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