Question

I’m using OpenGL in C++ Visual Studio 2008 Forms application and I want a GLcontrol to switch between 3D and 2D when a bool is set to true/false.

The drawing in 3D works fine, the drawing in 2D works fine, the problem comes when switching from one to another. So if I start the application drawing in 2D it works perfectly and the same with 3D, but if I change the boolean while running it won’t draw anything.

Here is the code where I change from one to another.

if(opciones->draw3D){
    GL::MatrixMode(MatrixMode::Modelview);
    GL::LoadIdentity();
    GL::Viewport(0, 0, w, h);
    Matrix4 lookat = Matrix4::LookAt(100, 100, 100, 0, 0, 0, 0, 0, 1);
    GL::LoadMatrix(lookat);
    GL::Scale(this->zoom, this->zoom, this->zoom);

    GL::Rotate(xrot, 1.0f, 0.0f, 0.0f);
    GL::Rotate(yrot, 0.0f, 1.0f, 0.0f);
    GL::Clear(ClearBufferMask::ColorBufferBit | ClearBufferMask::DepthBufferBit);
    GL::ClearColor(Color::LightGray);
// Draw3D
}
else {
    GL::MatrixMode(MatrixMode::Projection);
    GL::LoadIdentity();
    GL::Ortho(5, w-5, 5, h-5, -1, 1); 
    GL::Viewport(5, 5, w-5, h-5); 

    GL::Clear(ClearBufferMask::ColorBufferBit|ClearBufferMask::DepthBufferBit);
    GL::ClearColor(Color::LightGray);
    GL::MatrixMode(MatrixMode::Modelview);
    GL::LoadIdentity();

// Draw 2D
}

I don’t know what am doing wrong, but I guess that I don’t clear some matrix or something, because like I said before when the variable is draw3D==true at the beginning it draws perfectly and when the variable is draw3D==false at the beginning it draws perfectly in 2D, but the change during runtime makes it not work.

Answer 1

You need to set the projection matrix in 3D mode for one thing. I’m guessing by default your framework is setting up a perspective projection for you. This is getting overwritten when you do GL::Ortho() in the 2d part.