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on my university I got an assignment to build a program on OpenGl that read from a given txt file a coordinates of some lines and draw them to the screen.
i thank everyone that might help me, I know a little bit programming on C but I'm a little confused when it connects with OpenGl.
Thanks a lot.

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As described, the task splits into two clear parts: (1) read and parse the text file into a list of line segments, and (2) render those segments with an OpenGL context. As pointed out, having a small, working example makes debugging much easier. Below is a compact, practical approach that avoids OpenGL trickiness and keeps the C-side simple.

A robust parsing pattern (assumes each text line is "x1 y1 x2 y2"):

typedef struct { float x1,y1,x2,y2; } Line;

Line *lines = NULL;
size_t nlines = 0;

FILE *f = fopen("lines.txt","r");
if (!f) { perror("lines.txt"); exit(1); }

char buf[256];
while (fgets(buf, sizeof(buf), f)) {
    float a,b,c,d;
    if (sscanf(buf, "%f %f %f %f", &a,&b,&c,&d) == 4) {
        lines = realloc(lines, (nlines+1)*sizeof *lines);
        lines[nlines++] = (Line){a,b,c,d};
    }
}
fclose(f);

After loading, compute the bounding box (min/max of all coordinates), add a small margin, and set an orthographic projection so the file coordinates map directly to the view. For simple assignments the legacy pipeline is easiest:

glMatrixMode(GL_PROJECTION); glLoadIdentity();
glOrtho(minx-pad, maxx+pad, miny-pad, maxy+pad, -1, 1);
glMatrixMode(GL_MODELVIEW); glLoadIdentity();

glBegin(GL_LINES);
for (i=0; i<nlines; ++i) {
    glVertex2f(lines[i].x1, lines[i].y1);
    glVertex2f(lines[i].x2, lines[i].y2);
}
glEnd();

Troubleshooting notes: always check fopen/sscanf return values; watch for file format variations (commas, extra columns, header lines); remember OpenGL’s default Y axis is upwards (flip Y if the input uses screen coordinates). For larger datasets or modern learning goals, replace immediate mode with VBOs+shaders; for a quick university project the above is simpler and widely accepted.

Member Avatar for rubberman

Sorry, but we don't do your school work for you. Make an effort. Post your code and errors/problems you are having here and we may be able to help.

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