Add comments/documentation. Append checkHandle() and getHandle() definitions.

cameraInterface.cpp

// pylon_mex_camera_interface.cpp
// Code for StackOverflow Q&A: http://stackoverflow.com/a/32529850/2778484
// by Jon Chappelow (chappjc)
// For example MATLAB-side implementation (class wrapper), see https://github.com/chappjc/MATLAB/tree/master/cppClass

// Use:
//   1. Enumerate the different actions (e.g. New, Delete, Insert, etc.) in the
//      Actions enum.  For each enumerated action, specify a string (e.g.
//      "new", "delete", "insert", etc.) to be passed as the first argument to
//      the MEX function in MATLAB.
//   2. Customize the handling for each action in the switch statement in the
//      body of mexFunction (e.g. call the relevant C++ class method).
//  
// Implementation:
//
// For your C++ class, class_type, mexFunction uses static data storage to hold
// a persistent (between calls to mexFunction) table of integer handles and 
// smart pointers to dynamically allocated class instances.  A std::map is used
// for this purpose, which facilitates locating known handles, for which only 
// valid instances of your class are guaranteed to exist:
//
//    typedef unsigned int handle_type;
//    std::map<handle_type, std::shared_ptr<class_type>>
//
// A std::shared_ptr takes care of deallocation when either (1) a table element
// is erased via the "delete" action or (2) the MEX-file is unloaded.
//
// To prevent the MEX-file from unloading while a MATLAB class instances exist,
// mexLock is called each time a new C++ class instance is created, adding to
// the MEX-file's lock count.  Each time a C++ instance is deleted mexUnlock is
// called, removing one lock from the lock count.
//
// Requirements:
//
// A modern compiler with the following C++11 features:
//   - shared_ptr
//   - auto
//   - enum class
//   - initializer_list (for const map initialization)
// (VS2013, recent GCC possibly with -std=c++11, Clang since 3.1)

#include "mex.h"
#include <vector>
#include <map>
#include <algorithm>
#include <memory>
#include <string>
#include <sstream>

////////////////////////  BEGIN Step 1: Configuration  ////////////////////////
// Include your class declarations (and PYLON API).
#include <pylon/PylonIncludes.h>
#include <pylon/usb/PylonUsbIncludes.h>
#include <pylon/usb/BaslerUsbInstantCamera.h>
#include <pylon/PylonUtilityIncludes.h>

// Define class_type for your class
typedef CBaslerUsbInstantCameraArray class_type;

// List actions
enum class Action
{
    // create/destroy instance - REQUIRED
    New,
    Delete,
    // user-specified class functionality
    Capture
};

// Map string (first input argument to mexFunction) to an Action
const std::map<std::string, Action> actionTypeMap =
{
    { "new",        Action::New },
    { "delete",     Action::Delete },
    { "capture",    Action::Capture }
}; // if no initializer list available, put declaration and inserts into mexFunction

using namespace Pylon;
using namespace Basler_UsbCameraParams;

const String_t filenames[] = { "NodeMapCam1.pfs","NodeMapCam2.pfs" };
static const size_t camerasToUse = 2;
/////////////////////////  END Step 1: Configuration  /////////////////////////

// boilerplate until Step 2 below
typedef unsigned int handle_type;
typedef std::pair<handle_type, std::shared_ptr<class_type>> indPtrPair_type; // or boost::shared_ptr
typedef std::map<indPtrPair_type::first_type, indPtrPair_type::second_type> instanceMap_type;
typedef indPtrPair_type::second_type instPtr_t;

// getHandle pulls the integer handle out of prhs[1]
handle_type getHandle(int nrhs, const mxArray *prhs[]);
// checkHandle gets the position in the instance table
instanceMap_type::const_iterator checkHandle(const instanceMap_type&, handle_type);

void mexFunction(int nlhs, mxArray *plhs[], int nrhs, const mxArray *prhs[]) {

    // static storage duration object for table mapping handles to instances
    static instanceMap_type instanceTab;

    if (nrhs < 1 || !mxIsChar(prhs[0]))
        mexErrMsgTxt("First input must be an action string ('new', 'delete', or a method name).");

    char *actionCstr = mxArrayToString(prhs[0]); // convert char16_t to char
    std::string actionStr(actionCstr); mxFree(actionCstr);

    for (auto & c : actionStr) c = ::tolower(c); // remove this for case sensitivity

    if (actionTypeMap.count(actionStr) == 0)
        mexErrMsgTxt(("Unrecognized action (not in actionTypeMap): " + actionStr).c_str());

    // If action is not 'new' or 'delete' try to locate an existing instance based on input handle
    instPtr_t instance;
    if (actionTypeMap.at(actionStr) != Action::New && actionTypeMap.at(actionStr) != Action::Delete) {
        handle_type h = getHandle(nrhs, prhs);
        instanceMap_type::const_iterator instIt = checkHandle(instanceTab, h);
        instance = instIt->second;
    }

    //////// Step 2: customize each action in the switch in mexFuction ////////
    switch (actionTypeMap.at(actionStr))
    {
    case Action::New:
    {
        if (nrhs > 1 && mxGetNumberOfElements(prhs[1]) != 1)
            mexErrMsgTxt("Second argument (optional) must be a scalar, N.");

        handle_type newHandle = instanceTab.size() ? (instanceTab.rbegin())->first + 1 : 1;

        // Store a new CBaslerUsbInstantCameraArray in the instance map
        std::pair<instanceMap_type::iterator, bool> insResult = 
            instanceTab.insert(indPtrPair_type(newHandle, std::make_shared<class_type>(camerasToUse)));

        if (!insResult.second) // sanity check
            mexPrintf("Oh, bad news.  Tried to add an existing handle."); // shouldn't ever happen
        else
            mexLock(); // add to the lock count

        // return the handle
        plhs[0] = mxCreateDoubleScalar(insResult.first->first); // == newHandle

        // Get all attached devices and exit application if no device or USB Port is found.
        CTlFactory& tlFactory = CTlFactory::GetInstance();
        // Check if cameras are attached
        ITransportLayer *pTL = dynamic_cast<ITransportLayer*>(tlFactory.CreateTl(BaslerUsbDeviceClass));
        // todo: some checking here... (pTL == NULL || pTL->EnumerateDevices(devices) == 0)

        // Create and attach all Pylon Devices. Load Configuration
        CBaslerUsbInstantCameraArray &cameras = instance;
        DeviceInfoList_t devices;
        for (size_t i = 0; i < cameras.GetSize(); ++i) {
          cameras[i].Attach(tlFactory.CreateDevice(devices[i]));
        }

        // Open all cameras.
        cameras.Open();

        // Load Configuration and execute Trigger
        for (size_t i = 0; i < cameras.GetSize(); ++i) {
          CFeaturePersistence::Load(filenames[i], &cameras[i].GetNodeMap());
        }

        if (cameras[0].IsOpen() && cameras[1].IsOpen()) {
            mexPrintf("\nCameras are fired up and configuration is applied\n");

        break;
    }
    case Action::Delete:
    {
        instanceMap_type::const_iterator instIt = checkHandle(instanceTab, getHandle(nrhs, prhs));
        (instIt->second).close(); // may be unnecessary if d'tor does it
        instanceTab.erase(instIt);
        mexUnlock();
        plhs[0] = mxCreateLogicalScalar(instanceTab.empty()); // just info
        break;
    }
    case Action::Capture:
    {
        CBaslerUsbInstantCameraArray &cameras = instance; // alias for the instance

        // TODO: create output array and capture a frame(s) into it
        plhs[0] = mxCreateNumericArray(...);
        pixel_type* data = (pixel_type*) mxGetData(plhs[0]);
        cameras[0].GrabOne(...,data,...);
        // also for cameras[1]?
        }
    }
    default:
        mexErrMsgTxt(("Unhandled action: " + actionStr).c_str());
        break;
    }
    ////////////////////////////////  DONE!  ////////////////////////////////
}

handle_type getHandle(int nrhs, const mxArray *prhs[])
{
    if (nrhs < 2 || mxGetNumberOfElements(prhs[1]) != 1) // mxIsScalar in R2015a+
        mexErrMsgTxt("Specify an instance with an integer handle.");
    return static_cast<handle_type>(mxGetScalar(prhs[1]));
}

instanceMap_type::const_iterator checkHandle(const instanceMap_type& m, handle_type h)
{
    auto it = m.find(h);

    if (it == m.end()) {
        std::stringstream ss; ss << "No instance corresponding to handle " << h << " found.";
        mexErrMsgTxt(ss.str().c_str());
    }

    return it;
}