Question

I’ve been trying to incorporate shaders and OpenGl into a wxWidgets program. I’ve used the links below:

http://nehe.gamedev.net/article/glsl_an_introduction/25007/

http://www.lighthouse3d.com/tutorials/glsl-tutorial/hello-world-in-glsl/

Now I’ve been trying in a test program to use the shaders provided by the lighthouse3d tutorial and recreate the output, (a blue teapot spinning slowly on a white background). I can’t seem to get anything to draw though and all I can see is a black screen. My code so far is below, (I’m going to ignore most of the shaders intially as I’m 99% sure they’re fine):

void BasicGLPane::render( wxPaintEvent& evt )
{
    //wxGLCanvas::SetCurrent(*m_context);
    wxPaintDC(this); 
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
    //prepare2DViewport(0,0,getWidth()/2, getHeight());
    glLoadIdentity();
    gluLookAt(0.0,0.0,5.0, 
          0.0,0.0,-1.0,
          0.0f,1.0f,0.0f);

    glLightfv(GL_LIGHT0, GL_POSITION, lpos);
    //glRotatef(a,0,1,1);
    glutSolidTeapot(1);
    glFlush();
    //a+=0.1;

    SwapBuffers();
}

void BasicGLPane::InitializeGLEW()
{
    //prepare2DViewport(0,0,getWidth(), getHeight());
    // The current canvas has to be set before GLEW can be initialized.
    wxGLCanvas::SetCurrent(*m_context);
    GLenum err = glewInit();

    // If Glew doesn't initialize correctly.
    if(GLEW_OK != err)
    {
        std::cerr << "Error:" << glewGetString(err) << std::endl;
        const GLubyte* String = glewGetErrorString(err);
        wxMessageBox("GLEW is not initialized");
    }

BasicGLPane::BasicGLPane(wxFrame* parent, int* args) :
wxGLCanvas(parent, wxID_ANY, args, wxDefaultPosition, wxDefaultSize, wxFULL_REPAINT_ON_RESIZE)
{

    m_context = new wxGLContext(this);

    // To avoid flashing on MSW
    SetBackgroundStyle(wxBG_STYLE_CUSTOM);
}

I’ve had thoughts as to why I’m not getting any output. One thought I’m having is something to do with the m_context. I’m having to set the current context for WxWidgets before I can run GLEW. There’s also a number of properties that in the tutorial are initialized and I’m not using these functions in my wxWidgets version and I’m wondering if I should. These are:

glutInit(&argc, argv);
glutInitDisplayMode(GLUT_DEPTH | GLUT_DOUBLE | GLUT_RGBA);
glutInitWindowPosition(100,100);
glutInitWindowSize(320,320);
glutCreateWindow("MM 2004-05");

glutDisplayFunc(renderScene);
glutIdleFunc(renderScene);
glutReshapeFunc(changeSize);
glutKeyboardFunc(processNormalKeys);

glEnable(GL_DEPTH_TEST);
glClearColor(1.0,1.0,1.0,1.0);
glEnable(GL_CULL_FACE);

But I’m quite keen to avoid using glut and have managed to avoid it up until now. The only reason I’ve previously added it is to try and replicate the tutorial’s behaviour.

Edit:

I’m going to add a bit more as I have noticed one or two bits of odd behaviour. If I call this function in my draw:

void BasicGLPane::prepare2DViewport(int topleft_x, int topleft_y, int bottomrigth_x, int bottomrigth_y)
{
    glClearColor(1.0f, 1.0f, 1.0f, 1.0f); // Black Background
    glEnable(GL_TEXTURE_2D);   // textures
    glEnable(GL_COLOR_MATERIAL);
    glEnable(GL_BLEND);
    glDisable(GL_DEPTH_TEST);
    glBlendFunc(GL_SRC_ALPHA,GL_ONE_MINUS_SRC_ALPHA);

    glViewport(topleft_x, topleft_y, bottomrigth_x-topleft_x, bottomrigth_y-topleft_y);
    glMatrixMode(GL_PROJECTION);
    glLoadIdentity();

    gluOrtho2D(topleft_x, bottomrigth_x, bottomrigth_y, topleft_y);
    glMatrixMode(GL_MODELVIEW);
    glLoadIdentity();
}

I can get the background to change colour when I change the window size. I should also mention, it’s NOT refreshing every frame, It only draws one frame and then won’t call the render function again until I change the window size.

Answer 1

Turns out I didn’t need the gluLookAt in my render.