GTKD Cairo get pixel color

[Ola Fosheim Grøstad via Digitalmars-d-learn]

On Tuesday, 5 January 2016 at 23:26:12 UTC, Basile B. wrote:
> access to pix is easy...

This is the learn forum. Maybe one should be able to figure it 
out without asking, but there is nothing wrong with asking in 
depth on this forum. The threshold for asking should be low in 
here. At worst, nobody answers or as it turns out, posts a 
youtube video...