c - showing verticies in openGL -

i have program renders 3d wire mesh model using code fragment in loop.

glbegin(gl_lines); glcolor3f(.0f, 0.0f, 0.0f); glvertex3d(xs,ys,zs); glvertex3d(xe,ye,ze); glend(); 

i need add functionality vertices line starts , ends can rendered if user desires, using small shaded circle. circle should of constant screen size, 4-6 pixels across , rendered @ size independent of camera is, or how close is.

can suggest how render such vertex?

you can use gl_points in glbegin glpointsize function.