Here is a full answer using a small wrapper class to separate the c++ from objective-c code.
I had to raise another question on stackoverflow to deal with my poor c++ knowledge – but I have worked out everything we need to interface c++ cleanly with objective-c code, using the squares.cpp
sample code as an example. The aim is to keep the original c++ code as pristine as possible, and to keep the bulk of the work with openCV in pure c++ files for (im)portability.
I have left my original answer in place as this seems to go beyond an edit. The complete demo project is on github
CVViewController.h / CVViewController.m
-
pure Objective-C
-
communicates with openCV c++ code via a WRAPPER… it neither knows nor cares that c++ is processing these method calls behind the wrapper.
CVWrapper.h / CVWrapper.mm
- objective-C++
does as little as possible, really only two things…
- calls to UIImage objC++ categories to convert to and from UIImage <> cv::Mat
- mediates between CVViewController’s obj-C methods and CVSquares c++ (class) function calls
CVSquares.h / CVSquares.cpp
- pure C++
CVSquares.cpp
declares public functions inside a class definition (in this case, one static function).
This replaces the work ofmain{}
in the original file.- We try to keep
CVSquares.cpp
as close as possible to the C++ original for portability.
CVViewController.m
//remove 'magic numbers' from original C++ source so we can manipulate them from obj-C
#define TOLERANCE 0.01
#define THRESHOLD 50
#define LEVELS 9
UIImage* image =
[CVSquaresWrapper detectedSquaresInImage:self.image
tolerance:TOLERANCE
threshold:THRESHOLD
levels:LEVELS];
CVSquaresWrapper.h
// CVSquaresWrapper.h
#import <Foundation/Foundation.h>
@interface CVSquaresWrapper : NSObject
+ (UIImage*) detectedSquaresInImage:(UIImage*)image
tolerance:(CGFloat)tolerance
threshold:(NSInteger)threshold
levels:(NSInteger)levels;
@end
CVSquaresWrapper.mm
// CVSquaresWrapper.mm
// wrapper that talks to c++ and to obj-c classes
#import "CVSquaresWrapper.h"
#import "CVSquares.h"
#import "UIImage+OpenCV.h"
@implementation CVSquaresWrapper
+ (UIImage*) detectedSquaresInImage:(UIImage*) image
tolerance:(CGFloat)tolerance
threshold:(NSInteger)threshold
levels:(NSInteger)levels
{
UIImage* result = nil;
//convert from UIImage to cv::Mat openCV image format
//this is a category on UIImage
cv::Mat matImage = [image CVMat];
//call the c++ class static member function
//we want this function signature to exactly
//mirror the form of the calling method
matImage = CVSquares::detectedSquaresInImage (matImage, tolerance, threshold, levels);
//convert back from cv::Mat openCV image format
//to UIImage image format (category on UIImage)
result = [UIImage imageFromCVMat:matImage];
return result;
}
@end
CVSquares.h
// CVSquares.h
#ifndef __OpenCVClient__CVSquares__
#define __OpenCVClient__CVSquares__
//class definition
//in this example we do not need a class
//as we have no instance variables and just one static function.
//We could instead just declare the function but this form seems clearer
class CVSquares
{
public:
static cv::Mat detectedSquaresInImage (cv::Mat image, float tol, int threshold, int levels);
};
#endif /* defined(__OpenCVClient__CVSquares__) */
CVSquares.cpp
// CVSquares.cpp
#include "CVSquares.h"
using namespace std;
using namespace cv;
static int thresh = 50, N = 11;
static float tolerance = 0.01;
//declarations added so that we can move our
//public function to the top of the file
static void findSquares( const Mat& image, vector<vector<Point> >& squares );
static void drawSquares( Mat& image, vector<vector<Point> >& squares );
//this public function performs the role of
//main{} in the original file (main{} is deleted)
cv::Mat CVSquares::detectedSquaresInImage (cv::Mat image, float tol, int threshold, int levels)
{
vector<vector<Point> > squares;
if( image.empty() )
{
cout << "Couldn't load " << endl;
}
tolerance = tol;
thresh = threshold;
N = levels;
findSquares(image, squares);
drawSquares(image, squares);
return image;
}
// the rest of this file is identical to the original squares.cpp except:
// main{} is removed
// this line is removed from drawSquares:
// imshow(wndname, image);
// (obj-c will do the drawing)
UIImage+OpenCV.h
The UIImage category is an objC++ file containing the code to convert between UIImage and cv::Mat image formats. This is where you move your two methods -(UIImage *)UIImageFromCVMat:(cv::Mat)cvMat
and - (cv::Mat)cvMatWithImage:(UIImage *)image
//UIImage+OpenCV.h
#import <UIKit/UIKit.h>
@interface UIImage (UIImage_OpenCV)
//cv::Mat to UIImage
+ (UIImage *)imageFromCVMat:(cv::Mat&)cvMat;
//UIImage to cv::Mat
- (cv::Mat)CVMat;
@end
The method implementations here are unchanged from your code (although we don’t pass a UIImage in to convert, instead we refer to self
)