OpenGL and QT, crash at glDrawElements

[DaOnlyOwner]

Hi guys,
I am new here and new to OpenGL ;)

So I was trying to make something to appear on my screen, but unfortunately it always crashes at glDrawElements.
I am glad if somebody could help. Here is the code:

//Initialization 
void Mesh::initialize()
{
    this->initializeOpenGLFunctions();

    vao = new QOpenGLVertexArrayObject();
    vbo = new QOpenGLBuffer(QOpenGLBuffer::VertexBuffer);
    ebo = new QOpenGLBuffer(QOpenGLBuffer::IndexBuffer);

    vao->create();
    vbo->create();
    ebo->create();

    vao->bind();

        vbo->bind();
        vbo->setUsagePattern(QOpenGLBuffer::StaticDraw);
        vbo->allocate(vertices.data(),vertices.size() * sizeof(Vertex)); 


        ebo->bind(); 
        ebo->setUsagePattern(QOpenGLBuffer::StaticDraw);
        ebo->allocate(indices.data(),indices.size()*sizeof(GLuint)); 


        //Vertex position

        program->enableAttributeArray(0);
        program->setAttributeBuffer(0,GL_FLOAT,0,sizeof(Vertex));

        program->enableAttributeArray(1); 
        program->setAttributeBuffer(1,GL_FLOAT,offsetof(Vertex,Normal),3,sizeof(Vertex)); 

        glEnableVertexAttribArray(2);
        program->setAttributeBuffer(2,GL_FLOAT,offsetof(Vertex,TextCoords),2,sizeof(Vertex));

    vao->release();

}

It always crashes here:

void Mesh::DrawMesh()
{
    vao->bind();
    qDebug() << vertices.size();
    glDrawElements(GL_TRIANGLES, indices.size(),GL_UNSIGNED_INT,0);
    vao->release();
}

Note: When I call vao->isCreated() it returns false even tough I made sure (100%) that initialize() is called BEFORE DrawMesh.

Here is my Vertex struct:

struct Vertex
{
    QVector3D Position;
    QVector3D Normal;
    QVector2D TextCoords;
};

This is my vertex shader:

#version 330 core

layout(location=0) in vec3 position;
layout(location=1) in vec3 normal;
layout(location=2) in vec2 textCoords;

uniform mat4 MVP;

out vec4 color;

void main(void)
{
    gl_Position= MVP*vec4(position,1);
    color = vec4(1,1,1,1);
}

Can somebody help me? I'm really stuck here. Also I don't know if I can pass an array of QVector3D like that to the graphicscard...

Thank you really for your help. ;)

[A Former User]

Hi, welcome to the Qt forum! Seems like you forgot to create an OpenGL context and make it current, see: http://doc.qt.io/qt-5/qopenglfunctions.html#details

Edit: There is also a minimal example: http://doc.qt.io/qt-5/qtgui-openglwindow-example.html

[DaOnlyOwner]

@Wieland Thanks for the reply Wieland.
Inside paintGL I loop through a list of meshes and call the DrawMesh() method on all of them. I use a QOpenGLWidget for that.
So is manually creating a context still the recommended way to go?
Thanks you ;)

[A Former User]

@DaOnlyOwner said:

void Mesh::initialize()

That should be void Mesh::initializeGL(), in other words override void QOpenGLWidget::initializeGL(). Otherwise the function won't automatically use the correct OpenGL context. May I please see your Mesh header file?

[DaOnlyOwner]

@Wieland Of course,

class Mesh : public QOpenGLFunctions_3_3_Core
{
public:
    Mesh(const Mesh& mesh)
    {
        this->vertices = mesh.vertices;
        this->indices = mesh.indices;
        this->program = mesh.program;
        initialize();
    }

    Mesh(){}
    ~Mesh()
    {

        vao->destroy();
        vbo->destroy();
        ebo->destroy();

    }

    QVector<Vertex> vertices;
    QVector<GLuint> indices;
    QOpenGLShaderProgram* program;

    Mesh(const QVector<Vertex> &vertices, const QVector<GLuint> &indices, QOpenGLShaderProgram* program);
    void DrawMesh();

private:

    QOpenGLVertexArrayObject* vao;
    QOpenGLBuffer* vbo;
    QOpenGLBuffer* ebo;

    void initialize();

};

The code of my QOpenGLWidget:

void RenderingWindow::initializeGL()
{
    this->initializeOpenGLFunctions();    
    program->create();
    program->addShaderFromSourceFile(QOpenGLShader::Vertex, ":/testvert.vert" );
    program->addShaderFromSourceFile(QOpenGLShader::Fragment, ":/testfrag.frag");
    program->link();

    Camera::instance().LookAt(0,0,5, 0,0,0 ,0,1,0);
}

void RenderingWindow::resizeGL(int w, int h)
{
    Camera::instance().Perspective(60,w/h,0,10000);
}

void RenderingWindow::paintGL()
{
    program->bind();
        program->setUniformValue("MVP",Camera::instance().GetMVP());
        model.Draw();
    program->release();
}

void RenderingWindow::LoadModel()
{
    QString filename = QFileDialog::getOpenFileName(this,"Choose Model file",QString(),"Model files (*.fbx *.obj)");
    model.LoadModel(*this, filename, program);
}

model.Draw() goes through all the meshes currently attached to this model and draws them.

[A Former User]

Mesh(const Mesh& mesh) calls void Mesh::initialize(). Who calls Mesh(const Mesh& mesh)? The constructor must be called from within the correct OpenGL context.

[DaOnlyOwner]

@Wieland I think it's called when storing the Meshes inside a QVector. So the constructor is called somewhere in LoadModel().

[A Former User]

Ok. Then call makeCurrent() in void RenderingWindow::LoadModel().

[DaOnlyOwner]

@Wieland somehow It's still not working.
The reason why I have to call initialize() inside the copyConstructor is, that you can't copy QOpenGLVertexArrayObject..