Example: vision_capture_video_build_pyr

C++ example source code:

/* +------------------------------------------------------------------------+
   |                     Mobile Robot Programming Toolkit (MRPT)            |
   |                          https://www.mrpt.org/                         |
   |                                                                        |
   | Copyright (c) 2005-2023, Individual contributors, see AUTHORS file     |
   | See: https://www.mrpt.org/Authors - All rights reserved.               |
   | Released under BSD License. See: https://www.mrpt.org/License          |
   +------------------------------------------------------------------------+ */

#include <mrpt/gui/CDisplayWindow3D.h>
#include <mrpt/hwdrivers/CCameraSensor.h>
#include <mrpt/img/TColor.h>
#include <mrpt/opengl/Scene.h>
#include <mrpt/vision/CFeatureExtraction.h>
#include <mrpt/vision/CImagePyramid.h>
#include <mrpt/vision/TKeyPoint.h>
#include <mrpt/vision/types.h>

#include <chrono>
#include <iostream>
#include <thread>

using namespace std;
using namespace mrpt;
using namespace mrpt::gui;
using namespace mrpt::opengl;
using namespace mrpt::obs;
using namespace mrpt::vision;
using namespace mrpt::img;

// ------------------------------------------------------
//              TestVideoBuildPyr
// ------------------------------------------------------
void TestVideoBuildPyr()
{
    size_t N_OCTAVES = 4;
    bool do_smooth = false;
    bool do_grayscale = false;

    // Ask for a different number of octaves:
    cout << "Number of octaves to use [4]: ";
    {
        std::string s;
        std::getline(cin, s);
        int i = atoi(s.c_str());
        if (i > 0) N_OCTAVES = i;
    }

    // Show to the user a list of possible camera drivers and creates and open
    // the selected camera.
    cout << "Please, select the input video file or camera...\n";

    mrpt::hwdrivers::CCameraSensor::Ptr cam =
        mrpt::hwdrivers::prepareVideoSourceFromUserSelection();
    if (!cam) return;

    cout << "Video stream open OK\n";

    // Create 3D window:
    CDisplayWindow3D win("Demo of pyramid building from live video", 800, 600);

    //  Get the smart pointer to the main viewport object in this window,
    //   and create other viewports for the smaller images:
    std::vector<Viewport::Ptr> gl_views(N_OCTAVES);
    {
        Scene::Ptr& theScene = win.get3DSceneAndLock();
        gl_views[0] = theScene->getViewport("main");
        ASSERT_(gl_views[0]);

        // Create the other viewports:
        for (size_t i = 1; i < N_OCTAVES; i++)
            gl_views[i] = theScene->createViewport(format("view_%i", (int)i));

        // Assign sizes:
        //  It can be shown mathematically than if we want all viewports to be
        //  one next to each other
        //  horizontally so they fit to the viewport width (="1") and each is
        //  the half the previous one,
        //  the first one must have a width of 2^(n-1)/(2^n - 1)
        const double W0 =
            (double(1 << (N_OCTAVES - 1))) / ((1 << N_OCTAVES) - 1);

        double X = 0;
        double W = W0;
        for (size_t i = 0; i < N_OCTAVES; i++)
        {
            Viewport* vw = gl_views[i].get();
            vw->setViewportPosition(X, .0, W, 1.);
            // cout << "Created viewport " << i << " at X=" << X << " with
            // Width=" << W << endl;
            X += W;
            W *= 0.5;
        }

        // IMPORTANT!!! IF NOT UNLOCKED, THE WINDOW WILL NOT BE UPDATED!
        win.unlockAccess3DScene();
    }

    win.setPos(10, 10);

    win.addTextMessage(
        0.51, 5,  // X,Y<=1 means coordinates are factors over the entire
        // viewport area.
        "Keys: 's'=Smoothing, 'g': Grayscale 'f': Features",
        10  // An arbitrary ID
    );

    // The image pyramid: Initially empty
    CImagePyramid imgpyr;

    cout << "Close the window to end.\n";
    while (win.isOpen())
    {
        win.addTextMessage(5, 5, format("%.02fFPS", win.getRenderingFPS()));
        std::this_thread::sleep_for(1ms);

        // Grab new video frame:
        CObservation::Ptr obs = cam->getNextFrame();
        if (obs)
        {
            if (IS_CLASS(*obs, CObservationImage))
            {
                // Get the observation object:
                CObservationImage::Ptr o =
                    std::dynamic_pointer_cast<CObservationImage>(obs);

                // Update pyramid:
                imgpyr.buildPyramidFast(
                    o->image,  // This image is destroyed since we are calling
                    // the *Fast() version
                    N_OCTAVES, do_smooth, do_grayscale);

                win.get3DSceneAndLock();

                for (size_t i = 0; i < N_OCTAVES; i++)
                {
                    Viewport* vw = gl_views[i].get();
                    vw->setImageView(imgpyr.images[i]);
                }

                win.addTextMessage(
                    0.51, 25,  // X,Y<=1 means coordinates are factors over the
                    // entire viewport area.
                    format(
                        "Smooth=%i Grayscale=%i", int(do_smooth ? 1 : 0),
                        int(do_grayscale ? 1 : 0)),
                    11  // An arbitrary ID
                );

                win.unlockAccess3DScene();
                win.repaint();
            }

            if (win.keyHit())
            {
                mrptKeyModifier kmods;
                int key = win.getPushedKey(&kmods);

                if (key == MRPTK_ESCAPE) break;

                if (key == 's' || key == 'S') do_smooth = !do_smooth;
                if (key == 'g' || key == 'G') do_grayscale = !do_grayscale;
            }
        }
    }
}

// ------------------------------------------------------
//                      MAIN
// ------------------------------------------------------
int main()
{
    try
    {
        TestVideoBuildPyr();

        return 0;
    }
    catch (const std::exception& e)
    {
        std::cerr << "MRPT error: " << mrpt::exception_to_str(e) << std::endl;
        return -1;
    }
}