Line Drawing

[Keith Brown <brownk chem4823 usask ca>]

   I'd like to develop an application for drawing simple molecular
structures but I'm stuck at the starting gate. How does one draw a
straight line, erase a drawn line, change the colour of the line and
change the colour of the background? Admittedly, I haven't read the
tutorial cover to cover but there doesn't seem to be anything about these
questions there. Any help is much appreciated.

Keith