GL_LINE_LOOP

OpenGL OpenGL: Basic Coding
1

In the book that i have, the code below shows something that resembles a circle, but in the picture theres 8 points and in the code only 4. my question is, how do i find out the other coordinates to make something that looks as much as possible like a circle.

glBegin(GL_LINE_LOOP);
glVertex2f(-20,-20);
glVertex2f(-20,20);
glVertex2f( 20,20);
glVertex2f(20,-20);
glEnd();
2

glBegin(GL_LINE_LOOP);
for(float i=0; i<2pi; i++)
{
glVertex2f(20cos(i), 20sin(i));
}
glVertex2f(20,0);
glEnd();

something like that ought to do it.

3

Originally posted by chowe6685:
[b]glBegin(GL_LINE_LOOP);
for(float i=0; i<2pi; i++)
{
glVertex2f(20cos(i), 20sin(i));
}
glVertex2f(20,0);
glEnd();

something like that ought to do it.[/b]

Better make that for line as:
for(float i=0.f; i<2*PI; i+=PI/20.f)

/Alex

PS: 20.f is how much accuracy you want. Bigger values give better circles but you loose in speed. Experiment.

4

You don’t need that last glVertex (after the loop) because the line loop will automatically be closed. Had you used GL_LINE_STRIP, then the final glVertex call would be necessary.

5

thanks all i will give that a try. also something else, if i dont use a for loop instead use the vertex coordiantes, i will need atleast 8 or more points to make something that looks like a circle, how do i find those points?

6

You would still use sin/cos functions.

Originally posted by [TheFORCE]:
thanks all i will give that a try. also something else, if i dont use a for loop instead use the vertex coordiantes, i will need atleast 8 or more points to make something that looks like a circle, how do i find those points?