dev/file_grabber.cpp

This example shows how we would make a new device for a camera.We make a device that reads images from file. The only step missing here is to integrate the device into the YARP library.

Here's the header file, dev/FileFrameGrabber.h

/*
 * Copyright (C) 2006-2020 Istituto Italiano di Tecnologia (IIT)
 * Copyright (C) 2006-2010 RobotCub Consortium
 * All rights reserved.
 *
 * This software may be modified and distributed under the terms of the
 * BSD-3-Clause license. See the accompanying LICENSE file for details.
 */
 
#include <stdio.h>
#include <yarp/os/all.h>
#include <yarp/sig/all.h>
#include <yarp/dev/all.h>
 
class FileFrameGrabber : public yarp::dev::IFrameGrabberImage,
                         public yarp::dev::DeviceDriver {
private:
    std::string pattern, lastLoad;
    int first, last, at;
    int h, w;
 
    bool findImage(yarp::sig::ImageOf<yarp::sig::PixelRgb>& image) {
        bool triedFirst = false;
        char buf[1000];
        sprintf(buf,pattern.c_str(),at);
        while (!yarp::sig::file::read(image,buf)) {
            if (at==first) {
                if (triedFirst) {
                    return false;
                }
                triedFirst = true;
            }
            if (last==-1) {
                at = first;
            } else {
                at++;
                if (at>last) {
                    at = first;
                }
            }
            sprintf(buf,pattern.c_str(),at);
        }
        lastLoad = buf;
        h = image.height();
        w = image.width();
        return true;
    }
 
public:
    FileFrameGrabber() {
        pattern = "%d.ppm";
        first = last = -1;
        at = -1;
        h = w = 0;
    }
 
    bool open(const char *pattern, int first, int last) {
        this->pattern = pattern;
        this->first = first;
        this->last = last;
        at = first;
        yarp::sig::ImageOf<yarp::sig::PixelRgb> dummy;
        return findImage(dummy);
    }
 
    virtual bool open(yarp::os::Searchable& config) {
        std::string pattern =
            config.check("pattern",yarp::os::Value("%d.ppm")).asString();
        int first = config.check("first",yarp::os::Value(0)).asInt32();
        int last = config.check("last",yarp::os::Value(-1)).asInt32();
        return open(pattern.c_str(),first,last);
    }
 
    virtual bool close() {
        return true; // easy
    }
 
    virtual bool getImage(yarp::sig::ImageOf<yarp::sig::PixelRgb>& image) {
        bool ok = findImage(image);
        if (ok) {
            printf("showing image %s\n", lastLoad.c_str());
            at++;
            if (last!=-1 && at>last) {
                at = first;
            }
        }
        return ok;
    }
 
    virtual int height() const {
        return h;
    }
 
    virtual int width() const {
        return w;
    }
};

And here's how we can use it. In fact, we just grab the first image from the device.

/*
 * Copyright (C) 2006-2020 Istituto Italiano di Tecnologia (IIT)
 * Copyright (C) 2006-2010 RobotCub Consortium
 * All rights reserved.
 *
 * This software may be modified and distributed under the terms of the
 * BSD-3-Clause license. See the accompanying LICENSE file for details.
 */
 
#include <stdio.h>
#include <stdlib.h>
#include <yarp/dev/FrameGrabberInterfaces.h>
#include <yarp/dev/PolyDriver.h>
#include <yarp/dev/Drivers.h>
#include "FileFrameGrabber.h"
using namespace yarp::os;
using namespace yarp::sig;
using namespace yarp::dev;
 
int main(int argc, char *argv[]) {
    Network yarp;
 
    // give YARP a factory for creating instances of FileFrameGrabber
    DriverCreator *file_grabber_factory =
        new DriverCreatorOf<FileFrameGrabber>("file_grabber",
                                              "grabber",
                                              "FileFrameGrabber");
    Drivers::factory().add(file_grabber_factory); // hand factory over to YARP
 
    // use YARP to create and configure an instance of FileFrameGrabber
    Property config;
    if (argc==1) {
        // no arguments, use a default
        config.fromString("(device file_grabber) (pattern \"image/%03d.ppm\")");
    } else {
        // expect something like '--device file_grabber --pattern "image/%03d.ppm"'
        //                    or '--device dragonfly'
        //                    or '--device test_grabber --period 0.5 --mode [ball]'
        config.fromCommand(argc,argv);
    }
    PolyDriver dd(config);
    if (!dd.isValid()) {
        printf("Failed to create and configure a device\n");
        return 1;
    }
    IFrameGrabberImage *grabberInterface;
    if (!dd.view(grabberInterface)) {
        printf("Failed to view device through IFrameGrabberImage interface\n");
        return 1;
    }
 
    ImageOf<PixelRgb> img;
    grabberInterface->getImage(img);
    printf("Got a %dx%d image\n", img.width(), img.height());
 
    dd.close();
 
    return 0;
}