Example: opengl_multithread_rendering

C++ example source code:

/* +------------------------------------------------------------------------+
   |                     Mobile Robot Programming Toolkit (MRPT)            |
   |                          https://www.mrpt.org/                         |
   |                                                                        |
   | Copyright (c) 2005-2024, 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/containers/yaml.h>
#include <mrpt/core/lock_helper.h>
#include <mrpt/opengl/CAxis.h>
#include <mrpt/opengl/CFBORender.h>
#include <mrpt/opengl/CMesh.h>
#include <mrpt/opengl/CPointCloud.h>
#include <mrpt/opengl/CSphere.h>
#include <mrpt/opengl/Scene.h>
#include <mrpt/random.h>
#include <mrpt/system/CTimeLogger.h>
#include <mrpt/system/filesystem.h>
#include <mrpt/system/thread_name.h>

//#define USE_NANOGUI_WINDOW

#ifdef USE_NANOGUI_WINDOW
#include <mrpt/gui/CDisplayWindowGUI.h>
#else
#include <mrpt/gui/CDisplayWindow.h>
using my_window_t = mrpt::gui::CDisplayWindow;
#endif

#include <iostream>
#include <list>
#include <mutex>
#include <thread>

static const int RENDER_WIDTH = 600, RENDER_HEIGHT = 480;

auto& rng = mrpt::random::getRandomGenerator();
std::mutex rngMtx;

// sample scene:
static mrpt::opengl::Scene::Ptr generate_example_scene()
{
  auto s = mrpt::opengl::Scene::Create();

  {
    auto obj = mrpt::opengl::CAxis::Create(-5, -5, -5, 5, 5, 5);
    s->insert(obj);
  }
  {
    auto obj = mrpt::opengl::CSphere::Create(1.0f);
    obj->setColor_u8(0xff, 0x00, 0x00);
    obj->setLocation({1.0, 1.0, 1.0});
    s->insert(obj);
  }
  {
    auto obj = mrpt::opengl::CSphere::Create(0.25f);
    obj->setColor_u8(0x00, 0x00, 0xff);
    obj->setLocation({-1.0, -1.0, 0.25});
    obj->enableDrawSolid3D(false);
    s->insert(obj);
  }
  {
    auto obj = mrpt::opengl::CPointCloud::Create();

    auto lck = mrpt::lockHelper(rngMtx);
    for (int i = 0; i < 200; i++)
    {
      obj->insertPoint(
          rng.drawUniform(-3.0, 0.0), rng.drawUniform(-3.0, 0.0), rng.drawUniform(-3.0, 0.0));
    }
    obj->setPointSize(3.0f);
    s->insert(obj);
  }
  {
    using namespace std::string_literals;

    const std::string texture_file =
        mrpt::system::getShareMRPTDir() + "datasets/sample-texture-terrain.jpg"s;

    auto obj = mrpt::opengl::CMesh::Create();

    mrpt::img::CImage im;

    const int W = 128, H = 128;
    mrpt::math::CMatrixDynamic<float> Z(H, W);
    for (int r = 0; r < H; r++)
      for (int c = 0; c < W; c++) Z(r, c) = sin(0.05 * (c + r) - 0.5) * cos(0.9 - 0.03 * r);

    if (im.loadFromFile(texture_file))
    {
      obj->setZ(Z);
      obj->assignImageAndZ(im, Z);
      obj->setLocation(-5, 0, 0);
      obj->cullFaces(mrpt::opengl::TCullFace::BACK);
    }
    s->insert(obj);
  }

  return s;
}

mrpt::opengl::Scene::Ptr commonScene;
mrpt::system::CTimeLogger profiler;

struct RenderResult
{
  RenderResult() = default;

  std::string threadName;
  mrpt::img::CImage img;
  std::string labelText;
};

std::list<RenderResult> renderOutputs;
std::mutex renderOutputs_mtx;

static void renderer_thread_impl(const std::string name, const int period_ms, const int numImgs)
{
  using namespace std::string_literals;

  mrpt::system::thread_name(name);  // for debuggers

  mrpt::opengl::CFBORender::Parameters fboParams;
  fboParams.width = RENDER_WIDTH;
  fboParams.height = RENDER_HEIGHT;
  // fboParams.contextMajorVersion = 3;
  // fboParams.contextMinorVersion = 3;
  // fboParams.deviceIndexToUse = 0;
#ifdef _DEBUG
  fboParams.contextDebug = true;
#endif

  mrpt::opengl::CFBORender render(fboParams);
  mrpt::img::CImage frame(RENDER_WIDTH, RENDER_HEIGHT, mrpt::img::CH_RGB);

  // here you can put your preferred camera rendering position
  {
    auto& camera = render.getCamera(*commonScene);
    camera.setOrthogonal(false);

    auto lck = mrpt::lockHelper(rngMtx);
    camera.setZoomDistance(rng.drawUniform(15.0, 40.0));
    camera.setElevationDegrees(rng.drawUniform(20.0, 70.0));
    camera.setAzimuthDegrees(rng.drawUniform(-60.0, 60.0));

#if 0
        mrpt::containers::yaml d = mrpt::containers::yaml::Map();
        camera.toYAMLMap(d);
        std::cout << "Thread: " << name << "\nCamera:\n"
                  << d << "\n"
                  << std::endl;
#endif
  }

  const auto nameProfiler = name + "_render"s;

  for (int i = 0; i < numImgs; i++)
  {
    // render the scene
    if (i > 0) profiler.enter(nameProfiler);

    render.render_RGB(*commonScene, frame);

    if (i > 0) profiler.leave(nameProfiler);

    RenderResult res;
    res.img = frame.makeDeepCopy();
    res.labelText = mrpt::format("Img #%i", i);
    res.threadName = name;

    {
      auto lck = mrpt::lockHelper(renderOutputs_mtx);
      renderOutputs.emplace_back(std::move(res));
    }
    std::this_thread::sleep_for(std::chrono::milliseconds(period_ms));
  }
  std::cout << "\nRendering thread '" << name << "' ends." << std::endl;
}

static void renderer_thread(const std::string name, const int period_ms, const int numImgs)
{
  try
  {
    renderer_thread_impl(name, period_ms, numImgs);
  }
  catch (const std::exception& e)
  {
    std::cerr << "Thread '" << name << "' exception: " << e.what() << std::endl;
  }
}

#ifndef USE_NANOGUI_WINDOW
// wxWidgets frontend:
static void viz_thread()
{
  const double MAX_TIME = 10.0;
  const double t0 = mrpt::Clock::nowDouble();

  std::map<std::string, my_window_t::Ptr> wins;

  double t = 0;

  while ((t = mrpt::Clock::nowDouble() - t0) < MAX_TIME)
  {
    std::list<RenderResult> done;
    {
      auto lck = mrpt::lockHelper(renderOutputs_mtx);
      std::swap(done, renderOutputs);
    }

    for (auto& r : done)
    {
      auto& win = wins[r.threadName];
      if (!win)
      {
        // first time:
        win = my_window_t::Create(r.threadName, r.img.getWidth(), r.img.getHeight());
      }

      // update image:
      r.img.textOut(5, 5, r.labelText, mrpt::img::TColor::white());
      win->showImage(r.img);
    }

    std::this_thread::sleep_for(std::chrono::milliseconds(1));

    std::cout << "Showing images from working threads... " << t << "/" << MAX_TIME << "  \r";
  };

  std::cout << "\nVisualization thread ends." << std::endl;
}
#elif MRPT_HAS_NANOGUI
// nanogui frontend
static void viz_thread()
{
  try
  {
    mrpt::system::thread_name("viz");  // for debuggers

    nanogui::init();

    auto win = mrpt::gui::CDisplayWindowGUI::Create("main", 800, 600);

    win->performLayout();
    win->drawAll();
    win->setVisible(true);

#if 1
    win->background_scene_mtx.lock();
    win->background_scene = commonScene;
    win->background_scene_mtx.unlock();
#endif

    struct SubWindowData
    {
      SubWindowData() = default;

      nanogui::Window* win = nullptr;
      mrpt::gui::MRPT2NanoguiGLCanvas* glControl = nullptr;
      nanogui::Label* label = nullptr;
    };

    std::map<std::string, SubWindowData> subWindows;

    win->addLoopCallback(
        [&]()
        {
          std::list<RenderResult> done;
          {
            auto lck = mrpt::lockHelper(renderOutputs_mtx);
            std::swap(done, renderOutputs);
          }
          if (done.empty()) return;

          for (auto& r : done)
          {
            auto& sw = subWindows[r.threadName];
            if (!sw.win)
            {
              // Add subwindow:
              sw.win = new nanogui::Window(win.get(), r.threadName);
              sw.win->setLayout(new nanogui::GroupLayout());

              sw.label = sw.win->add<nanogui::Label>("label");

              sw.glControl = sw.win->add<mrpt::gui::MRPT2NanoguiGLCanvas>();
              sw.win->setPosition({5 + 100 * (subWindows.size() - 1), 10});
              sw.win->setFixedWidth(350);
              {
                auto scene = mrpt::opengl::Scene::Create();
                auto lck = mrpt::lockHelper(sw.glControl->scene_mtx);
                sw.glControl->scene = std::move(scene);
              }
              win->performLayout();
            }

            {
              auto lck = mrpt::lockHelper(sw.glControl->scene_mtx);
              sw.glControl->scene->getViewport()->setImageView(std::move(r.img));
            }
            sw.label->setCaption(r.labelText);
          }
        });

    nanogui::mainloop();
    nanogui::shutdown();

    std::cout << "\nVisualization thread ends." << std::endl;
  }
  catch (const std::exception& e)
  {
    std::cerr << "[viz_thread] Error:\n" << e.what() << std::endl;
  }
}
#endif

// ------------------------------------------------------
//              TestMultithreadRendering
// ------------------------------------------------------
static int TestOffscreenRender()
{
  commonScene = generate_example_scene();

  std::vector<std::thread> allThreads;

#ifdef USE_NANOGUI_WINDOW
  {
    // ==================================================================
    //                         ** CRITICAL **
    // Create dummy FBO Renderer to init GL as required by FBOs *before*
    // nanogui initializes it. Otherwise, GL context errors will be
    // raised by FBOs later on.
    // ==================================================================
    mrpt::opengl::CFBORender render(10, 10);
  }
#endif

  allThreads.emplace_back(&viz_thread);
  std::this_thread::sleep_for(std::chrono::milliseconds(1000));

  allThreads.emplace_back(&renderer_thread, "one", 5 /*period*/, 600 /*nImgs*/);

  allThreads.emplace_back(&renderer_thread, "two", 6 /*period*/, 700 /*nImgs*/);

  for (auto& t : allThreads)
    if (t.joinable()) t.join();

  return 0;
}

// ------------------------------------------------------
//                      MAIN
// ------------------------------------------------------
int main(int argc, char* argv[])
{
  try
  {
#if MRPT_HAS_NANOGUI
    return TestOffscreenRender();
#else
    std::cerr << "This example requires MRPT built with NANOGUI.\n";
    return 1;
#endif
  }
  catch (const std::exception& e)
  {
    std::cerr << "MRPT error: " << mrpt::exception_to_str(e) << std::endl;
    return -1;
  }
}