cv:circle function draw multiple circles with a single call - c++

Question

I'm new with OpenCV library, and I would like to use it to detect circles in a video stream captured from an iPad's back camera. I figured out how to do it and with OpenCV 2.4.2, it can be done in less than 10 lines of code. But it doesn't work for me, and I think I missed something because of some weird behaviours I obtain.
The code is very simple and begins in the Objective-C callback triggers each time a new frame is captured by the camera. Here is what I do in this callback:
- (void)captureOutput:(AVCaptureOutput *)captureOutput
didOutputSampleBuffer:(CMSampleBufferRef)sampleBuffer
fromConnection:(AVCaptureConnection *)connection
{
// Convert CMSampleBufferRef to CVImageBufferRef
CVImageBufferRef imageBuffer = CMSampleBufferGetImageBuffer(sampleBuffer);
// Lock pixel buffer
CVPixelBufferLockBaseAddress(imageBuffer, kCVPixelBufferLock_ReadOnly);
// Construct VideoFrame struct
uint8_t *baseAddress = (uint8_t*)CVPixelBufferGetBaseAddress(imageBuffer);
size_t width = CVPixelBufferGetWidth(imageBuffer);
size_t height = CVPixelBufferGetHeight(imageBuffer);
size_t stride = CVPixelBufferGetBytesPerRow(imageBuffer);
// Unlock pixel buffer
CVPixelBufferUnlockBaseAddress(imageBuffer, 0);
std::vector<unsigned char> data(baseAddress, baseAddress + (stride * height));
// Call C++ function with these arguments => (data, (int)width, (int)height)
}
And here is the C++ function that process the image with OpenCV:
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
}
The image retrieve from iPad's back camera is in BGRA (32 bits) format.
What I expected was an image from the iPad's back camera with a simple circle drawn at the position x = 300px, y = 200px and with a radius of 30px.
And this is what I got: http://i.stack.imgur.com/bWfwa.jpg
Do you know what is wrong with my code?
Thanks in advance.

Answer 1

Thanks for your help, I finally figured out what happen, and it's my entire fault...
When you create a new Mat you need to pass it the image's height as first argument, and not width. The circle is drawn properly if I switch the arguments.