Basic usage

Assuming your graphical library has a classical setpixelrgb() procedure and you know your z values will be for example in the [0, 2] range, you can write something like:

use forcolormap, only: Colormap, wp
...
type(Colormap) :: cmap
integer  :: red, green, blue
real(wp) :: z, x, y
...
! Let's use the lajolla Scientific colormap:
call cmap%set("lajolla", 0.0_wp, 2.0_wp)
...
z = f(x,y)
call cmap%compute_RGB(z, red, green, blue)
call setpixelrgb(x, y, red, green, blue)

The library is using the precision wp=>real64 defined in the module iso_fortran_env. And depending on the integers expected by your graphical library, you may need to convert the kinds of red, green, blue variables.