I have a list of contours to draw. Some of these contours intersect themselves.
When I want to draw them with OpenCV, I simply use the cv::drawContours function.
However, the behavior is quite strange.
Here is a quote of the official documentation
C++: void drawContours(InputOutputArray image, InputArrayOfArrays contours, int contourIdx, const Scalar& color, int thickness=1, int lineType=8, InputArray hierarchy=noArray(), int maxLevel=INT_MAX, Point offset=Point() )
Parameters:
contourIdx – Parameter indicating a contour to draw. If it is negative, all the contours are drawn.
So, from the documentation, if I want to draw all my areas, filled in black, I just have to do:
cv::drawContours(this->mask.raw,
this->areas, -1,
cv::Scalar(0,0,0),
cv::FILLED);
However, this gives me the following ouput:
Here, we can clearly see that all my areas are NOT filled in black.
But if I loop over my areas list and call cv::drawContours for each area:
unsigned int i = 0;
for (const auto& area : this->areas)
cv::drawContours(this->mask.raw,
this->areas, i++,
cv::Scalar(0,0,0),
cv::FILLED);
I got the good ouput which is quite different from the first one:
Have I missed something from the documentation? Could someone explain me the behavior of cv::drawContours and what is the different of calling it one for all areas and calling it each time for each area?
