OpenCV draw a simple circle

gistfile1.cpp

void proccessImage(std::vector<unsigned char>& imageData, int width, int height)
{
	// Create cv::Mat from std::vector<unsigned char>
	Mat src(width, height, CV_8UC4, const_cast<unsigned char*>(imageData.data()));
	Mat final;

	// Draw a circle at position (300, 200) with a radius of 30
	cv::Point center(300, 200);
	circle(src, center, 30.f, CV_RGB(0, 0, 255), 3, 8, 0);

	// Convert the gray image to RGBA
	cvtColor(src, final, CV_BGRA2RGBA);

	// Reform the std::vector from cv::Mat data
	std::vector<unsigned char> array;
	array.assign((unsigned char*)final.datastart, (unsigned char*)final.dataend);
	
	// Send final image data to GPU and draw it
}