OpenGL-How do I draw randomly non-overlapping circle - c++

Question

I've already draw few random placed circle, but I want different numbers of circles every time I run the program. So the question really is how do I call a function in random times?
I also need them to have convex and concave effects but unable to arrange them to random circles.
Finally, I need circles not to overlap, how do I do that?
Below is my partial code so far.
void circle(){
double r=50;
int dx, dy;
dx=rand()%350;
dy=rand()%250;
glLineWidth(1);
glEnable(GL_LINE_SMOOTH);
glBegin(GL_LINES);
double i=1.0;
double j=0.0;
for (double y=r; y>=-r; y=y-1) {
i=i-0.01;
j=j+0.01;
//glColor3f(i, i, i);
glColor3f(j, j, j);
glVertex2f(-sqrt(r*r-y*y)+dx, y+dy);
glVertex2f(sqrt(r*r-y*y)+dx, y+dy);
}
glEnd();
}
void display(void){
glClear(GL_COLOR_BUFFER_BIT);
srand((unsigned)time(0));
circle();
circle();
circle();
glEnd();
glFlush();
}

Answer 1

The simple approach
It is enough to pick a random number and iterate. This can cause the circles to overlap.
int min_circles = 10;
int max_circles = 100;
int amount = min_circles + rand()%(max_circles-min_circles+1);
for (int i = 0; i < amount; i++)
circle();
Non overlapping
This is not a trivial matter and has been an interesting research topic. You can have several approaches to this problem for example:
Naïve Generation
Store all previously added circle positions and if you try to add a new one just do a check with the previous for overlapping. If it overlaps choose another position. If it fails several times in a row then stop.
Easing
You can also consider treating all circles as a system of points connected with springs and iterate a few times so that the springs will repel the circles from each other thus conforming to the non-overlapping rule.
Poisson Disk Sampling
You can read up on implementing Poisson Disk Sampling on the internet. The algorithm generates a uniform random distribution of points on a plane so that they are at certain distance from each other. Then just use these points as centers of circles.

Answer 2

how do I call a function in random times?
that one way of doing it:
if (rand() % someNumber == 0)
callFunc();
I also need them to have convex and concave effects but unable to arrange them to random circles.
i didnt understand what you mean.
Finally, I need circles not to overlap, how do I do that?
first you need to creaye circles in a structure, and store them in a collection. assume you the structure like that:
struct Circle {
float x, y, raduis;
}
and a collection like that:
std::vector<Circle> circles;
then the creation may look like that:
Circle c;
do {
bool canExit = true;
c.x = rand()*350;
c.y = rand()*250;
c.radius = 50;
for (int i = 0; i < circles.size(); i++) {
float dx = (circles[i].x - c.x);
float dy = (circles[i].y - c.y);
floar radii = circles[i].radius + c.radius;
if (dx*dx + dy*dy < (radii*radii) ) {
canExit = false;
break;
}
}
while(canExit == false);
circles.push_back(c);
of cours thats only may way, hope it works for you, and good luck.