Visualization of the scene within a real-time loop

[robinpassama]

Hello Sofa Community !

Sorry if the question has already been raised, but after many searches I found no answer for my concerns.

I am trying to translate a python code (using an old version of Sofa) into a C++ library (using latest release of Sofa, 24.06.00). This code implements a real-time loop that simulates deformation of an object. The C++ translation of the simulation in itself should not be a big deal, but I face trouble in implementing the visualization loop. My main problems are:

• to avoid blocking instructions due to visualization, because the resulting code will be used in a time constrained control loop.
• optimally to get only a visualization of the scene (not all buttons of the GUI), because everything related to visualization must be controlled by user code.

The existing Python code roughly looks like:

import Sofa
#other initialization instructions ...
root = Sofa.Core.Node("myroot")
#create the scene ...
Sofa.Simulation.init(root)
init_display(root)
while True
    #instructions to update scene...
    Sofa.Simulation.animate(root, 0.1)
    Sofa.Simulation.updateVisual(root)
    render(root)
   #get data from simulation to perform other computations...

with init_display and render functions implementing opengl based rendering, roughly :

def init_display(node):
    # init openGL and windowing library
    Sofa.SofaGL.glewInit()
    Sofa.Simulation.initVisual(node)
    Sofa.Simulation.initTextures(node)
    ...
    glLoadIdentity()

def render(rootNode):
    # reset openGL buffers...
    Sofa.SofaGL.draw(rootNode)
   #rendering using windowing library

What I would like is to do mostly the same in C++. It would be fantastic if I could simply use OpenGL and GLUT for instance. As far as I understood the video tutorial it is not supported by default by recent versions of Sofa: either we use the GUI or we are terminal only without visualization.

In a first step I start with the "oneTetrahedron" example:

#include <sofa/core/objectmodel/Context.h>
//other includes and using directives...
int main(int argc, char** argv)
{
   //program initialization...
    sofa::component::init();
    sofa::simulation::graph::init();
    
    sofa::gui::init();
    sofa::gui::common::GUIManager::Init(argv[0]);

    const auto groot = sofa::simulation::getSimulation()->createNewGraph("root");
    //building the scene graph...
    
    const VisualStyle::SPtr style = sofa::core::objectmodel::New<VisualStyle>();
    groot->addObject(style);
    sofa::core::visual::DisplayFlags& flags = *style->displayFlags.beginEdit();
    flags.setShowNormals(false);
   //... setting other display flags
    style->displayFlags.endEdit();

    sofa::gui::common::GUIManager::SetScene(groot);

    sofa::simulation::node::initRoot(groot.get());
    groot->setAnimate(false);

    sofa::gui::common::GUIManager::MainLoop(groot);
    sofa::simulation::graph::cleanup();
    return 0;
}

Then I need to replace the sofa::gui::common::GUIManager::MainLoop(groot); instruction (and probably related initialization code), that is blocking, with a code similar to previous python code. I found nothing in the API to do that...

I would like something that could look like:

void display() {
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
    glLoadIdentity();
    // make Sofa drawing in the opengl buffer...
    glutSwapBuffers();
}

int main(int argc, char** argv) {
    sofa::component::init();
    sofa::simulation::graph::init();
    auto groot = sofa::simulation::getSimulation()->createNewGraph("root");
    //building the scene graph and setting display flags as previously...
    #initialize glut...
    glutDisplayFunc(display);

    sofa::simulation::node::initRoot(groot.get());
    groot->setAnimate(false);
   
    while (true) {
        //performing some actions on the scene...
        //controlling animation and getting result
        glutMainLoopEvent();//render one frame
        usleep(16000);            //at ~ 60Hz
    }
    return 0;
}

So what I need, I believe, is a way to make Sofa filling the openGL buffer in the display function. I tried many things but nothing seems to work...

Could someone tell me if there is a simple way to achieve this in Sofa 24.06.00 ?
Otherwise even a complex/incomplete example code where to start from would be really appreciated !

[robinpassama]

I finally found the way (based on SofaGLFW plugin for those interested) !