planet's topography controlled

Randomized fbm and iq turbulence are nice, but I also need a way to control planet's topography and continent's shape. 

I therefore added some specialized code to do it : submitting the following bitmap, containing an example of continent map, to the new shaders  :

Black pixels (0,0,0) simply represents oceans and rivers; green channel is dedicated for plains and continents coasts altitude, and blue channel is reserved for areas where mountains are authorized; I get the following results: