Question

I just started working with OpenGL, but I ran into a problem after implementing a Font system.

My plan is to simply visualize several Pathfinding Algorithms.

Currently OpenGL gets set up like this (OnSize gets called once on window creation manually):

void GLWindow::OnSize(GLsizei width, GLsizei height)
{
    // set size
    glViewport(0,0,width,height);

    // orthographic projection
    glMatrixMode(GL_PROJECTION);
    glLoadIdentity();
    glOrtho(0.0,width,height,0.0,-1.0,1.0);
    glMatrixMode(GL_MODELVIEW);

    m_uiWidth = width;
    m_uiHeight = height;
}

void GLWindow::InitGL()
{
    // enable 2D texturing
    glEnable(GL_TEXTURE_2D);
    // choose a smooth shading model
    glShadeModel(GL_SMOOTH);
    // set the clear color to black
    glClearColor(0.0, 0.0, 0.0, 0.0);

    glEnable(GL_ALPHA_TEST);
    glAlphaFunc(GL_GREATER, 0.0f);  
}

In theory I don’t need blending, because I will only use untextured Quads to visualize obstacles and line etc to draw paths… So everything will be untextured, except the fonts…

The Font Class has a push and pop function, that look like this (if I remember right my Font system is based on a NeHe Tutorial that I was following quite a while ago):

inline void GLFont::pushScreenMatrix()
{
    glPushAttrib(GL_TRANSFORM_BIT);
    GLint   viewport[4];
    glGetIntegerv(GL_VIEWPORT, viewport);
    glMatrixMode(GL_PROJECTION);
    glPushMatrix();
    glLoadIdentity();
    glOrtho(viewport[0],viewport[2],viewport[1],viewport[3], -1.0, 1.0);
    glPopAttrib();
}

inline void GLFont::popProjectionMatrix()
{
    glPushAttrib(GL_TRANSFORM_BIT);
    glMatrixMode(GL_PROJECTION);
    glPopMatrix();
    glPopAttrib();
}

So the Problem:
If I don’t draw a Text I can see the Quads I want to draw, but they are quite dark, so there must be something wrong with my general OpenGL Matrix Properties.
If I draw Text (so the font related push and pop functions get called) I can’t see any Quads.

The question:
How do I solve this problem and some background information why this happened would also be nice, because I am still a beginner/student, who just started.

Answer 1

If your quads are untextured, you will run into undefined behaviour. What will probably happen is that any previous texture will be used, and the colour at point (0,0) will be used, which could be what is causing them to be invisible.

Really, you need to disable texturing before trying to draw untextured quads using glDisable(GL_TEXTURE_2D). Again, if you don’t, it’ll just use the previous texture and texture co-ordinates, which without seeing your draw() loop, I’m assuming to be undefined.