我遇到了一个奇怪的问题，我试图旋转的对象突然消失了。我想旋转对象的方法是按下一个键，它会将全局变量rotateAnimation设置为true。当变量rotateAnimation为false时，对象是可见的，但一旦为true，对象就消失了。
下面是代码：

bool rotateAnimation = false;
bool moveAnimation = false;
int moveDirX = 1, moveDirY = 1;

void DrawSpiral(int x, int y)
{
    float tx, ty;
    float i;
    float a = 0, b = 0;

    glPointSize(3);
    glBegin(GL_LINE_STRIP);

    for (i = 0; i < 20; i = i + 0.025)
    {
        a = a + .05;
        b = b + .05;
        tx = x + b * cos(i);
        ty = y + a * sin(i);
        glVertex2f(tx, ty);
    }
    glEnd();
}

void DrawSquare(int x, int y, int size)
{
    glBegin(GL_POLYGON);

    glVertex2f(x, y);
    glVertex2f(x - size, y);
    glVertex2f(x - size, y - size);
    glVertex2f(x, y - size);

    glEnd();
}

void DrawPolygon(int x, int y)
{
    glBegin(GL_POLYGON);

    glVertex2f(x, y);
    glVertex2f(x - 25, y - 25);
    glVertex2f(x - 15, y - 53);
    glVertex2f(x + 15, y - 53);
    glVertex2f(x + 25, y - 25);

    glEnd();
}

void init()
{
    glViewport(0, 0, WINDOW_WIDTH, WINDOW_HEIGHT);
    glMatrixMode(GL_PROJECTION); // Since I want to do rotation in 2D

    glLoadIdentity();

    glClearColor(1.0, 1.0, 1.0, 0);
    glColor3f(0.0f, 0.0f, 0.0f);

    gluOrtho2D(0, WINDOW_WIDTH, 0, WINDOW_HEIGHT);
}

void Keypress(int key, int x, int y)
{
    switch (key)
    {

    case 'm':
        moveAnimation = !moveAnimation;
        break;

    case 'o':
        rotateAnimation = !rotateAnimation;
        break;
    }
}

void Display()
{
    glClear(GL_COLOR_BUFFER_BIT);

    staticScene(); // Some other drawings that should always be there on the screen

    glPushMatrix();
    if (rotateAnimation)
    {
        glRotatef(60, 1.0, 0.0, 0.0);
    }

    glColor3f(0.0f, 0.0f, 0.0f);
    glPointSize(2);

    if (shape == "square")
        DrawSquare(X, Y, 40);
    else if (shape == "polygon")
        DrawPolygon(X, Y);
    else if (shape == "spiral")
        DrawSpiral(X, Y);
    glPopMatrix();

    glutSwapBuffers();
}

void timer(int value)
{
    glutPostRedisplay();
    glutTimerFunc(1000 / 60, timer, 0);

    if (moveAnimation)
    {
        int dx = 2, dy = 2;

        if (X - dx < 0) // Add from X
            X += dx, moveDirX = 1;
        else if (X + dx > drawingWindow[0].first) // Subtract to X
            X -= dx, moveDirX = -1;
        else
            X += (dx * moveDirX);

        if (Y - dy < drawingWindow[2].second) // Add from Y
            Y += dy, moveDirY = 1;
        else if (Y + dy > drawingWindow[0].second) // Subtract to Y
            Y -= dy, moveDirY = -1;
        else
            Y += (dy * moveDirY);
    }
}

当rotateAnimation为假时：

当rotateAnimation为真时：

EDIT：我也尝试缩放对象，但是同样的事情发生了，当开关打开时，对象消失，当开关关闭时，对象出现。我注意到的一件事是，当我注解掉TimerFunc时，什么也没有发生。对象scale或rotate也没有发生，这取决于开关打开了什么。