Smooth lines which aren't able to be made flat

Hi everybody.
I came with a very simple question.
I have a problem with usage of flat lines. Although I tried disabling GL_LINE_SMOOTH and also turned off GL_BLEND mode, lines are still smooth. what is my mistake here about that if there is? If there is not, what is the main reason of it. Is it because of the structure behind SFML or something else?


a lot of graphic cards have some extra settings to improve rendering. mostly multisample and antialising.
look at you settings and disable them.
anyway you should post a screenshot to show what you mean.


Here is what I mean:

I wanted the line on the left to be drawn with pixels in same color, not with semi-pixels to give a smooth effect.That is, I don’t want to work with blured pixels because it isn’t suitable when making a paint-like editor or things similar to it using glReadPixels after rendering the line as one of the useful primitives of OpenGL.There should be a certain solution without external adjustment for that issue.
Thanks in advance.