2d opengl line not the same size after mirroring

OpenGL OpenGL: Basic Coding
1

hallo together,

i am a bit new to opengl. i am working with opengl via the openframeworks toolkit. i have a question about drawing a line and then mirroring it and draw it again. my problem is that this line dont looks the same when i draw it mirrored. the best would be if you look to the atached pic below (it is a 500% zoomed screenshot of my 1 pixel line):

here are some code snippets which i tried:


void testApp::draw(){

    ofPushMatrix();
    ofTranslate(1024/2+60,768/2);

    glBegin(GL_LINES);
        glVertex2f(30,0);
        glVertex2f(35.0,5.0);
    glEnd();
    glBegin(GL_LINES);
        glVertex2f(35.0,5.0);
        glVertex2f(35.0,19.0);
    glEnd();
    glBegin(GL_LINES);
        glVertex2f(35.0,19.0);
        glVertex2f(34.0,20.0);
    glEnd();
    glBegin(GL_LINES);
        glVertex2f(20,0);
        glVertex2f(15.0,5.0);
    glEnd();
    glBegin(GL_LINES);
        glVertex2f(15.0,5.0);
        glVertex2f(15.0,19.0);
    glEnd();
    glBegin(GL_LINES);
        glVertex2f(15.0,19.0);
        glVertex2f(16.0,20.0);
    glEnd();
    ofPopMatrix();

    ofPushMatrix();
    ofTranslate(1024/2+30,768/2);

    glBegin(GL_LINE_STRIP);
        glVertex2f(30,0);
        glVertex2f(35.0,5.0);
        glVertex2f(35.0,19.0);
        glVertex2f(34.0,20.0);
    glEnd();
    glBegin(GL_LINE_STRIP);
        glVertex2f(20,0);
        glVertex2f(15.0,5.0);
        glVertex2f(15.0,19.0);
        glVertex2f(16.0,20.0);
    glEnd();
    ofPopMatrix();

    ofPushMatrix();
    ofTranslate(1024/2,768/2);

    for(int j=0;j<2;j++){
        glBegin(GL_LINE_STRIP);
        glVertex2f(0,0);
        glVertex2f(5.0,5.0);
        glVertex2f(5.0,19.0);
        glVertex2f(4.0,20.0);
        glEnd();

        ofRotateZ(180);
        ofRotateX(180);
        ofTranslate(10,0);
    }

    ofPopMatrix();

    ofPushMatrix();
    ofTranslate(1024/2+30,768/2);

    for(int j=0;j<2;j++){
        glBegin(GL_LINE_STRIP);
        glVertex2f(0,0);
        glVertex2f(5.0,5.0);
        glVertex2f(5.0,19.0);
        glVertex2f(4.0,20.0);
        glEnd();

        glScalef(-1, 1, 1);
        ofTranslate(10,0);
    }
    ofPopMatrix();
}

all the snippets failed.
so i think you see what my problem is.
my question now is: is it be posibble to draw the line that it exactly looks the same like the first one? or is this not possible cause of antialiasing and other issues?

2

hallo people,

hope you all had a nice christmas.
i had some time during the xmas days so i tried again to fix my problem but without success. are there any german speaking people around here so that i can write down my problem in german language maybe then i can better describe my problem.
i searched around on many different pages but the only solutions which come near my problem was that it maybe has something todo with the size of the opengl window and a distortion trough the window size. changing my opengl window has also no success. anny ideas what is going wrong. anyone also working with 1px thin lines?

3

hey guys, i got it,

found it here:
http://www.gamedev.net/community/forums/topic.asp?topic_id=556634

a line is not a line, it is a rect. so i positioned it not on 0 but rather on 0.5 and the problem is away.