How to draw line in OpenGl?

问题

I want to draw a line in opengl.

 glBegin(GL_LINES);
    glVertex2f(.25,0.25);
    glVertex2f(.75,.75);
glEnd();

this code draw line but if i want to draw a line from coordinate(10,10) to coordinate(20,20) what will i do ?

what it means (.25,.25) and (.75, .75) ?

回答1:

(.25, .25) and (.75,.75) are line's start and end point.

To draw a line from (10,10) to (20,20):

glBegin(GL_LINES);
    glVertex2f(10, 10);
    glVertex2f(20, 20);
glEnd();

回答2:

Each point value in glVertex2f is between -1 and 1, bottom left is (-1, -1), top right is (1,1) and center is (0, 0).

To map an absolute point to normalized space:

• Divide x through by the window width, w, to get the point in the range from 0 to 1.

• Multiply it by 2 to get the range from 0 to 2.

• Subtract 1 to get the desired -1 to 1 range.

• Repeat for y value and windows height ,h.

For example:

double x1 = 10;
double y1 = 10;
double x2 = 20;
double y2 = 20;

x1 = 2*x1 / w - 1;
y1 = 2*y1 / h - 1;

x2 = 2*x2 / w - 1;
y2 = 2*y2 / h - 1;

glBegin(GL_LINES);
    glVertex2f(x1, y1);
    glVertex2f(x2, y2);
glEnd();

来源：https://stackoverflow.com/questions/14486291/how-to-draw-line-in-opengl