## Sunday, March 23, 2014

### How to Draw Circle in OpenGL

In the OpenGL Computer graphics there major problem in drawing circle. In this post we are going to study How to Draw Circle in OpenGL. There is no primitive functions like of lines, points, triangles and other polygons for circle, hence drawing a circle need some new method/function from our side. we are going to learn that today.

There are many methods of Drawing circle in OpenGL, we going to discuss one by one each of them.

### First Method - using the indefinite points

This method used the no of of point to draw a circle. The problem with this method is you need more precession as we use the sine and cosine function with the value of pie as 3.14159, So little error may in the round circle. Put the following code in a simple display function and run the program for your circle. See the Image it's output -

glBegin(GL_POINTS);
for(int i=0;i<1000;++i)
{
glVertex3f(cos(2*3.14159*i/1000.0),sin(2*3.14159*i/1000.0),0);
}
glEnd();

### Second Method - using the lines

As Like above program circles can be created using the small sets of lines.We used the bunch of lines, which are closed together to go round forming a circle. For drawing circle in opengl, this method also used the simple sine and cosine maths functions, but we have not used pie instead go for degree for angles.

typedef struct
{
float x;
float y;
}CIRCLE;

CIRCLE circle;

void createcircle (int k, int r, int h) {
glBegin(GL_LINES);
for (int i = 0; i < 180; i++)
{
circle.x = r * cos(i) - h;
circle.y = r * sin(i) + k;
glVertex3f(circle.x + k,circle.y - h,0);

circle.x = r * cos(i + 0.1) - h;
circle.y = r * sin(i + 0.1) + k;
glVertex3f(circle.x + k,circle.y - h,0);
}
glEnd();
}

If you know about the structures in C then fine you understand the typedef else we have more object oriented approach making use of classes for C++. Same program above in classes.

class circle{
public : float x,y,rot;

public:
void createcircle (int k, int r, int h);

};
void circle::createcircle (int k, int r, int h) {
glBegin(GL_LINES);
for (int i = 0; i < 180; i++)
{
x = r * cos(i) - h;
y = r * sin(i) + k;
glVertex3f(x + k,y - h,0);

x = r * cos(i + 0.1) - h;
y = r * sin(i + 0.1) + k;
glVertex3f(x + k,y - h,0);
}
glEnd();
}

#### 39 comments:

1. ya sir i got it il just go through it if any modifications il let you know bt i have a another project same like a story as u heard of ant and bird an ant wil be stuckd in river it seeks help and bird helps it by dropping a leaf so in turn of exchange can i have any algorithm project using opengl

2. im not getting any algorithm sir

3. sir you said you wil try to make changes if i ger thus project so in turn of buying i exchanged it so ca n you stil do any modifications

4. of real appearance of animals

5. offcourse i am trying to do that

6. ok sir if you modify any real appearance of animals let me know and may i know that hanoi of tower program is been executed successfully

7. Tower of Hanoi Project is working fine here in mysystem so do it will in your's

8. rajeev sir i need source codw of algorithm if u have any algorithm suggest me

9. rajeev sir i need a source code of any algorithm except lru sstf

10. which algorithm there are many here

11. Gudnght our lecturer said he wil give a topic algorithm tomorrow to do a mini project using opengl c++ so i will let you know the topic tomorrow

12. hi rajeev sir do have any project based on freedom fighters like image of chitradurga fort and onaki obavva hits soldiers who come way hidden in forts of rocks and can say which project you have based on algorithm of os and any other as i am not gettng any idea about that rply me as soon you can get the message

13. In visual c++ it is not giving output. its showing as 0 succeeded, 0 failed, 1 up-to-date,
how to get a output?

14. sir the speed of transfer of rings from 1 to 3 is very high...how to reduce the transfer speed

15. sir rajeev sir kindly help me in mini project on algorithm

16. can i have any 3d project

17. k fine i have shooting of objects in exchange can i have any 3d mini project using opengl

18. there are many algorithm projects in here

why you not trying them or just mention one

19. can i have any 3d a wonderfull project

20. first decide exactly what you want?

21. i need one amazing worthy 3d mini project based on some tag line

22. do you have any idea as i have not much time

23. hi rajeev sir actually i don hav any idea on 3d some of my friend doing 3d home with furnitured so if you have any3d projects let me knw

24. hi rajeev sir am trying out from long days and texting you that can i have one wonderful and interesting cg project using c++ opengl if its cost also i have a some other projects can exchange it as i did it with hare and tortoise project with lru page replacement algorithm sourcecode

25. if it is 3d also no problem

26. rajeev sir rply to my message let me know

27. i am a bit busy with my work so not able to concentrate on the things........

28. k sir fine but if you're free send me one interesting project if it cost i have source code of some wil exchange

29. the movement of the rings is too fast how to slow it

30. Sir plz send me code link...available link is not working

31. Depolkarnikhil@gmail.com

32. Code link not working.Plz help Sir.tylorabcd@gmail.com

33. sir is this hanoi project of using opengl functions

34. I have sent to you the mail with source cod links

35. check your mail from openglprojects@gmail.com it has link for the hare tortoise projects

36. Get free project in exchange of any one that not published here

37. sir i asked you for a algorithm sourcecode

38. Pls can I get source code for tower of Hanoi pls pls

39. source code for hare and the tortoise story