Visibility against an unknown background

[Odalrick]

I need to draw visible lines on pictures with wxPython. That means I
can't simply use, for instance, a black line since it wont be visible
on a black or dark picture.

Painting applications like the GIMP accomplish this by altering the
colour of the line based on the colour of the pixel it covers, but the
only way I can think of doing that is getting each pixel, transforming
the colour then painting it on the screen, which seems like a horribly
inefficient way do it.

I could use alternating colour on the lines, but I don't think that
will be good enough for my taste.

I think I will use a partially transparent bitmap with a hole in the
appropriate place and move the hole as needed.

I realized the last solution as I was writing this and I think it will
work fairly well, but I'm still wondering if there is another, better
solution i might have missed.

/Odalrick