Creating a Camera with OpenGL 3.3 and Qt 5.6

Question

I'm quite new to OpenGL and Qt and I've been so far so good with it. Rendering a simple triangle with OpenGL 3.3 wasn't that hard but integrating a Camera is. For some reason my triangle dissappears!? Did I get the math wrong to calculate the matrices? I used these 2 tutorials as a starting point: http://www.opengl-tutorial.org/beginners-tutorials/tutorial-3-matrices/

https://wiki.qt.io/How_to_use_OpenGL_Core_Profile_with_Qt

My code(the most important parts only):

void GLWidget::initializeGL()
{
    QGLFormat glFormat = QGLWidget::format();
    if ( !glFormat.sampleBuffers() )
        qWarning() << "Could not enable sample buffers";

    // Set the clear color to black
    glClearColor( 0.0f, 0.0f, 0.0f, 1.0f );

    // Prepare a complete shader program…
    if ( !prepareShaderProgram( "A:/Projekte/Qt Workspace/Projects/CGOpenGL/simple.vert", "A:/Projekte/Qt Workspace/Projects/CGOpenGL/simple.frag" ) )
        return;

    /////Matrix calculations/////
    projection.perspective(45.0f, 4.0f / 3.0f, 0.1f, 100.0f);
    view.lookAt(QVector3D(4,3,3),QVector3D(0,0,0),QVector3D(0,1,0));
    model = QMatrix4x4();
    //////////


    // We need us some vertex data. Start simple with a triangle ;-)
    GLfloat points[] = {-0.5f, -0.5f, 0.0f,
                        1.0f, 0.5f, -0.5f,
                        0.0f, 1.0f, 0.0f,
                        0.5f, 0.0f, 1.0f};
    vertexBuffer.create();
    vertexBuffer.setUsagePattern( QGLBuffer::StaticDraw );
    if ( !vertexBuffer.bind() )
    {
        qWarning() << "Could not bind vertex buffer to the context";
        return;
    }
    vertexBuffer.allocate( points, 3 * 4 * sizeof( float ) );

    // Bind the shader program so that we can associate variables from
    // our application to the shaders
    if ( !shader.bind() )
    {
        qWarning() << "Could not bind shader program to context";
        return;
    }

    // Enable the "vertex" attribute to bind it to our currently bound
    // vertex buffer.
    shader.setAttributeBuffer( "vertex", GL_FLOAT, 0, 4 );
    shader.enableAttributeArray( "vertex" );
}

void GLWidget::paintGL()
{
    // Clear the buffer with the current clearing color
    glClear( GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT );

    // Set the MVP variable in the shader
    shader.setUniformValue("MVP",projection * view * model);

    // Draw stuff
    glDrawArrays( GL_TRIANGLES, 0, 3 );
}

Vertex Shader:

#version 330

layout(location = 0) in vec3 vertexPosition_modelspace;
uniform mat4 MVP;

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

Answer 1

you made a call to

shader.enableAttributeArray( "vertex" );

yet named it:

vertexPosition_modelspace

in the shader, you need to change the names to be consistent.

Try renaming the variable in the shader to "vertex"