Drawing Sinusoidal wave as well as straight line using Gimp

Currently I am making use of Gimp 2.6 and the Script-Fu works fine.

Make use of Shape paths which helps in creating sine waves 
ref:- http://registry.gimp.org/node/59
sample image generated using Shape paths
http://induino.librelab.org/2013/09/hello-world.html


To know where to download the shape-path-0.91.scm, check out the path using
Edit->preference->Folders->Scripts
mine is
/home/ranjit/.gimp-2.6/scripts
/usr/share/gimp/2.0/scripts
save the file in /home/ranjit/.gimp-2.6/scripts
after downloading the http://registry.gimp.org/files/shape-path-0.91.scm to the given location, close the gimp and launch it again or refresh the scirpt-Fu
Filter -> Script-Fu -> Refresh Script
A new tool bar is included called Script-Fu.

Drawing a straight line using Gimp
- select the path tool
- click on two different point in the image, this will highlight the line between those two points
- select stoke path and define the parameters
That's it

There are other ways of drawing st line, make use of the best friend called google :)