glBegin(GL_LINES);
    for (int i = -WORLD_SIZE; i <= WORLD_SIZE; i += GRID_SIZE) {

        glVertex3i(-WORLD_SIZE, -1, i);
        glVertex3i(WORLD_SIZE, -1, i);

        glVertex3i(i, -1, WORLD_SIZE);
        glVertex3i(i, -1, -WORLD_SIZE);
    }
    glEnd();c