3D screen precision of OpenGL

hello everybody....

when i need to draw line by one of line algorithms using glvertix3f , it seemed to be as number of points in a Straight line , but my problem is that there is many of free pixels appeared between each two adjacent point , So how can I exceed this problem and make each two adjacent points be Convergent , also the Straight line appear smooth ??

the problem that drawing line appear as folow::

.................................................. .................................................. ...................

But i need it smooth as follow:

__________________________________________________ ________________________

thanks in advance