一、FPS摄像机

题目：能否修改摄像机类，使得其能够变成一个真正的FPS摄像机（不能随意飞行，只能待在xz平面上）；

在camera.h中的ProcessKeyboard()函数中添加一行代码：Position.y = 0.0f;使y轴一直为0

    void ProcessKeyboard(Camera_Movement direction, float deltaTime)
    {
        float velocity = MovementSpeed * deltaTime;
        if (direction == FORWARD)
            Position += Front * velocity;
        if (direction == BACKWARD)
            Position -= Front * velocity;
        if (direction == LEFT)
            Position -= Right * velocity;
        if (direction == RIGHT)
            Position += Right * velocity;
        Position.y = 0.0f;
    }

二、创建观察矩阵

题目：手动创建一个观察矩阵，替换LookAt()函数；

QMatrix4x4 myLookAt(QVector3D position, QVector3D target, QVector3D worldUp)
{
    //z轴向量（摄像机反方向）
    QVector3D zaxis = QVector3D(position - target); //摄像机的位置 - 原点
    zaxis.normalize();

    worldUp.normalize();
    //x轴向量（右轴）
    QVector3D xaxis = QVector3D::crossProduct(worldUp, zaxis);
    xaxis.normalize();
    
        //y轴向量（上轴）
    QVector3D yaxis = QVector3D::crossProduct(zaxis, xaxis); 
    
    QMatrix4x4 translation; 
    QVector4D theVector4D;
    theVector4D.setX(-position.x()); // Third column, first row
    theVector4D.setY(-position.y());
    theVector4D.setZ(-position.z());
    theVector4D.setW(1.0);
    translation.setColumn(3,theVector4D);
    QMatrix4x4 rotation;
    theVector4D.setX(xaxis.x()); // First column, first row
    theVector4D.setY(xaxis.y());
    theVector4D.setZ(xaxis.z());
    theVector4D.setW(0.0);
    rotation.setColumn(0,theVector4D);
    theVector4D.setX(yaxis.x()); 
    theVector4D.setY(yaxis.y());
    theVector4D.setZ(yaxis.z());
    theVector4D.setW(0.0);
    rotation.setColumn(1,theVector4D);
    theVector4D.setX(zaxis.x());
    theVector4D.setY(zaxis.y());
    theVector4D.setZ(zaxis.z());
    theVector4D.setW(0.0);
    rotation.setColumn(2,theVector4D);
    
    return rotation * translation;
}

注：观看OpenGL中文官网（https://learnopengl-cn.github.io/）和阿西拜的现代OpenGL入门（https://ke.qq.com/course/3999604#term_id=104150693）学习OpenGL