Segmentation fault calling QOpenGLContext::create()

RoApPr

Good day to all! I am trying to run a computational shader on OpenGL 4.3 in a Qt console application. I read about the context and format, and even found the same topic - https://forum.qt.io/topic/52688/console-application-with-opengl/2 - however, that code cannot be executed, because when calling '.create()' for any object, a segfault occurs.
No matter what I did, I couldn't get around this problem.
I am grateful in advance for any help!

Christian Ehrlicher

Please provide a minimal compilable example to reproduce the problem. Also your environment would be interesting.

RoApPr

@Christian-Ehrlicher , In general, a minimal example is given by the link I gave (for this, actually), but here is my code:

.pro file:

QT += gui

CONFIG += c++11 console
CONFIG -= app_bundle

# You can make your code fail to compile if it uses deprecated APIs.
# In order to do so, uncomment the following line.
#DEFINES += QT_DISABLE_DEPRECATED_BEFORE=0x060000    # disables all the APIs deprecated before Qt 6.0.0

SOURCES += \
        main.cpp

# Default rules for deployment.
qnx: target.path = /tmp/$${TARGET}/bin
else: unix:!android: target.path = /opt/$${TARGET}/bin
!isEmpty(target.path): INSTALLS += target

main.cpp:

#include <QOpenGLShaderProgram>
#include <QGuiApplication>
#include <QSurfaceFormat>
#include <QOpenGLContext>
#include <QOffscreenSurface>
#include <QOpenGLFunctions_4_3_Core>
#include <QDebug>

//void compute();

int main(int argc, char *argv[])
{
    QCoreApplication a(argc, argv);

    QSurfaceFormat format;
    format.setVersion(4, 3);
    format.setProfile(QSurfaceFormat::CoreProfile);
    //QSurfaceFormat::setDefaultFormat(format);

    QOpenGLContext context;
    context.setFormat(format);
    context.create();

    QOffscreenSurface surface;
    surface.create();

    context.makeCurrent(&surface);

    QOpenGLFunctions_4_3_Core *fun = context.versionFunctions<QOpenGLFunctions_4_3_Core>();// context.functions();
    //QOpenGLFunctions *fun = context.functions();
    fun->initializeOpenGLFunctions();

    QOpenGLShaderProgram m_program;
    QOpenGLShader cShader(QOpenGLShader::Compute);
    cShader.compileSourceFile("/GA_comp_shader.glsl");
    m_program.addShader(&cShader);
    if ( !m_program.link() ) {
        qWarning( "Error: unable to link a shader program." );
    }
    else {qWarning( "Able to link a shader program." );}

    GLuint m_GA_uniform_pop_size = m_program.uniformLocation("pop_size");
    GLuint m_GA_uniform_A = m_program.uniformLocation("A");
    GLuint m_GA_uniform_B = m_program.uniformLocation("B");
    GLuint m_GA_uniform_C = m_program.uniformLocation("C");
    GLuint m_GA_uniform_D = m_program.uniformLocation("D");
    GLuint m_GA_uniform_E = m_program.uniformLocation("E");

    int popul_size = 1000;

    QVector<float> population(popul_size);
    for (int i = 0; i < popul_size; i++) {
        population[i] = i;
    }
    QVector<float> fitness(popul_size);

    GLuint bufObjHandles[2];
    fun->glGenBuffers(2, bufObjHandles);

    fun->glBindBuffer(GL_SHADER_STORAGE_BUFFER, bufObjHandles[0]);
    fun->glBufferData(GL_SHADER_STORAGE_BUFFER, population.size() * sizeof(float), population.data(), GL_DYNAMIC_DRAW);
    fun->glBindBuffer(GL_SHADER_STORAGE_BUFFER, bufObjHandles[1]);
    fun->glBufferData(GL_SHADER_STORAGE_BUFFER, fitness.size() * sizeof(float), fitness.data(), GL_DYNAMIC_DRAW);

    fun->glBindBufferBase(GL_SHADER_STORAGE_BUFFER, 0, bufObjHandles[0]);
    fun->glBindBufferBase(GL_SHADER_STORAGE_BUFFER, 1, bufObjHandles[1]);

    int pop_size = 500;
    float A = 1.05; float B = -3.1; float C = 1.05; float D = 10; float E = 2;

    if ( !m_program.bind() )
        qWarning( "Error: unable to bind a shader program." );

    m_program.setUniformValue(m_GA_uniform_pop_size, pop_size);
    m_program.setUniformValue(m_GA_uniform_A, A);
    m_program.setUniformValue(m_GA_uniform_B, B);
    m_program.setUniformValue(m_GA_uniform_C, C);
    m_program.setUniformValue(m_GA_uniform_D, D);
    m_program.setUniformValue(m_GA_uniform_E, E);

    fun->glDispatchCompute(256,1,1);
    fun->glMemoryBarrier(GL_SHADER_STORAGE_BARRIER_BIT);

    float *result = (float*)fun->glMapBufferRange(GL_SHADER_STORAGE_BUFFER, 0, pop_size*sizeof(float), GL_MAP_READ_BIT);

    m_program.release();
    return a.exec();
}

RoApPr

@Christian-Ehrlicher , Oh, and the shader, of course:

#version 430 core

layout (local_size_x = 128, local_size_y = 1, local_size_z = 1) in;

uniform float pop_size;
uniform float A;
uniform float B;
uniform float C;
uniform float D;
uniform float E;

layout (std430, binding = 0) buffer Individuals {
  float individuals[];
};

layout (std430, binding = 1) buffer FitnessValues {
  float fitnessValues[];
};

void main() {
  uint gid = gl_GlobalInvocationID.x;
  float individual = individuals[gid];

  // Calculate the fitness value for the current individual
  float fitness;
  for (int i = 0; i < 10000; i++) {
    fitness = (i + 1358/145.548) * A * individual + sqrt(abs(B)*individual) / sqrt(abs(C)*individual) - pow(sqrt(abs(D)*individual), sqrt(sqrt(sqrt(sqrt(sqrt(sqrt(E)))))));
    fitness = (i/2 + 98641/14524.285548) * A * individual + sqrt(abs(B)*individual) / sqrt(abs(C)*individual) - pow(sqrt(abs(D)*individual), sqrt(sqrt(sqrt(sqrt(sqrt(sqrt(E)))))));
    fitness = (i*1.5 - 13/1.548) * A * individual + sqrt(abs(B)*individual) / sqrt(abs(C)*individual) - pow(sqrt(abs(D)*individual), sqrt(sqrt(sqrt(sqrt(sqrt(sqrt(E)))))));
  }
  fitnessValues[gid] = fitness;
}

This code is definitely working, because everything starts in QWidgets and is considered correct, but nothing wants to work in the console application :)

Christian Ehrlicher

@RoApPr You need at least a QGuiApplication because e.g. QOpenGLContext is in QtGui.

RoApPr

@Christian-Ehrlicher , I not completely understand - i MUST to create graphical window before using my code block? And there is no way to bypass the restriction?

jsulm

@RoApPr said in Segmentation fault calling QOpenGLContext::create():

i MUST to create graphical window before using my code block

No, you need to create an QGuiApplication instance.

RoApPr

@jsulm , thank you very much! And thank you, @Christian-Ehrlicher , very much as well!