[Cin] Again on plugins in floating point (HDR)

[Andrea paz]

> The only thing I'd like to mention is that for a long time I've been
> wondering why the VideoScope Waveform doesn't show image levels that
> exceed 100%. Is it because these levels don't exist?

Yes, on this aspect I have done many tests. Without Andrew's patches
the scopes always show clipping 0 - 100%.
With Andrew's patches, RGBA-FLOAT color model and X11 graphics driver;
the scopes also show out-of-range values. The display stops at -10% or
+110% but there is no clip, in fact by varying the brightness all
out-of-range values become visible, even over 110%. The only caveat is
to disable the "smooth" option which always causes clipping.

One problematic consequence is the vectorscope also showing values
outside the circle making its reading difficult, if not incorrect.

https://streamable.com/obd7rv

Consider that I used exr images from tests that have brightness values
as high as 100 and above (compared to the usual 0 - 1.0 range); which
is not realistic. I think the strange colors you see in the video are
due to these excessive values; however, they could be an indication of
some problem of CinGG to handle HDR.