在lwjgl / opengl中的3D场景上绘制2D叠加层

Question

I'm trying to draw a hud that displays the fps of the application over the top of a 3d scene. I know the answer to this question has something to do with changing the initialization code, and switching it back. You know, this stuff:

GL11.glEnable(GL11.GL_BLEND);
GL11.glBlendFunc(GL11.GL_SRC_ALPHA, GL11.GL_ONE_MINUS_SRC_ALPHA);
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
glOrtho(0, 800, 600, 0, 1, -1);
glMatrixMode(GL_MODELVIEW);

This is the code i need to render the 2d part of the screen. On a related note, i'm having a hard time understanding what all of this code does, and haven't found a good resource on it. Can anyone point me in the right direction. Most tutorials don't include the setup code, i think they assume people know what to use(But i don't!).

Answer 1

I am using these methods:

public static void make3D() {

    glPopAttrib();
    glPushAttrib(GL_ENABLE_BIT);

    glEnable(GL_DEPTH_TEST);
    glDepthFunc(GL_LEQUAL);

    glViewport(0,0,SCREEN_WIDTH,SCREEN_HEIGHT);
    glMatrixMode(GL_PROJECTION);
    glLoadIdentity();

    // FOV = Field of View
    // Aspect ration
    // zNear and zFar (Viewing range)
    gluPerspective(FOV,(float) SCREEN_WIDTH / SCREEN_HEIGHT,0.1f,1000f);

    glMatrixMode(GL_MODELVIEW);
    glLoadIdentity();

}

For changing to 3D view, and

public static void make2D() {

    glPopAttrib();
    glPushAttrib(GL_ENABLE_BIT);

    glViewport(0,0,SCREEN_WIDTH,SCREEN_HEIGHT);
    glMatrixMode(GL_PROJECTION);
    glLoadIdentity();
    glOrtho(0, SCREEN_WIDTH, SCREEN_HEIGHT,0,-1,1);
    glMatrixMode(GL_MODELVIEW);
    glLoadIdentity();

}

for changing to 2D view.

Java doesnt seem to have any problem with this, please correct me if i'm wrong !