Smudge to an empty layer; Mixer brush to an empty layer

[JodyC]

Please add smudge to an empty layer and paint mixer brush to an empty layer to Affinity Photo 2 for iPad, so that they are not destructive to the layer below.

 

[loukash]

Also for the desktop version: +1!
As far as I'm concerned, every brush tool should have the Current Layer & Below mode.

[Olidoesaffinity]

I would love it if the functionality of "sample current layer and below" could be added to the Paint Mixer Brush. 

[keiichi77]

Also mixer brush doesn't understand opacity, so it mixes/changes semi-transparent black to full 100% cover paint black, though semi transparent black contains just e.g. 5 percent of the 'pigments', and 95% 'water'.