find all points in a circle - opencv

Question

I draw a circle with a fixed input Point. Now I really want to get a vector of all the Points in that circle includes filled area inside. I tried the code below but it only get the border. I can not use Contours function because I have used it many times so it would be very complicated. Please give me advice thank you so much
vector<Point> allpoints;
Point center = Point(370, 200);
void getPoints()
{
Size axes(20, 20);
ellipse2Poly(center, axes, 0, 0, 360, 1, allpoints);
}
void draw(Mat &BGR_frame)
{
circle(BGR_frame, center, 20, Scalar(0, 255, 0),CV_FILLED ,2);
getPoints();
}

Answer 1

A simple approach is to draw the circle on a black initialized mask, and retrieve the non-black points from there:
void draw(Mat &BGR_frame)
{
circle(BGR_frame, center, 20, Scalar(0, 255, 0),CV_FILLED ,2);
// Black initialized mask, same size as 'frame'
Mat1b mask(frame.rows, frame.cols, uchar(0));
// Draw white circle on mask
circle(mask, center, 20, Scalar(255), CV_FILLED, 2);
// Find non zero points on mask, and put them in 'allpoints'
findNonZero(mask, allpoints);
}
Alternatively, you can scan all pixels of the matrix, and keep points that satisfy the equation of being internal points of the circle:
Point c(370, 200);
int r = 20;
void draw(Mat &BGR_frame)
{
circle(BGR_frame, c, r, Scalar(0, 255, 0),CV_FILLED ,2);
for (int y = 0; y < mask.rows; ++y) {
for (int x = 0; x < mask.cols; ++x) {
// Check if this is an internal point
if ((x - c.x)*(x - c.x) + (y - c.y)*(y - c.y) <= (r*r)) {
allpoints.push_back(Point(x,y));
}
}
}
}