draw a line on a cube

hi

I want to draw a line on a cube like this image .But i’m having only two vertex for line …

help regarding this…

i) glScissor(not sure as i m beginner and jumping and jumping)
ii) Texture which have line made by hand(read texture mapping and some few tutorial lie on net for that)

hi,

its a line vertex while drawing i want to cut as line in the cube ,showing the depth…