[vlc-devel] full screen overlay for automatic projection mapping

Andras Szalai slymsg at gmail.com
Fri Oct 4 01:38:29 CEST 2019

I am trying to develop a filter plugin to fix some projection issues for my
home cinema setup. I got as far as writing and compiling a simple
out-of-tree video filter plugin that modifies the video by moving some
pixels around.

Eventually I want to be able to do an automatic calibration. The filter
would work in tandem
with a companion smartphone app. The filter plugin would render some
specific patterns on the full screen output, the smartphone app would
analyze the patterns and communicate back to the plugin somehow. This would
be great for correcting for wobbly projection screens.

The problem I am having is that filter plugins work on the video, not on
the output, so I don't have a way to render to the "black areas".

I want to avoid writing an output plugin as that would be a lot more work
and would be platform dependent.

My video filter plugin can potentially resize the video to match the size
of the output, but this would be inefficient and everything downstream of
the plugin would be working on a larger resolution video.

I am new to VLC internals. Is there a way to render an overlay (e.g. a
checkerboard pattern) from a filter plugin such that it potentially covers
the entire full screen output?

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