Hi,

I've created patches that add option to mix source images with the
black backgrounds of rgbparade and vectorscope filters.

The rationale for the change is that user must to be able to correlate
the outputs of meters visually with the images that produce these
outputs.

On single monitor applications like Flowblade the only way to do this
is to make the backgrounds of meters display source image mixed with
black in a user defined ratio.

The functionality was added in such a way, that current users of
vectorscope and rgbparade will not see any change in behaviour or
performance, unless values of new parameters "mix" and "overlay sides"
are changed.

Patches are attached, please apply.


Janne