我正在尝试在OpenGL中创建一个基于四元数的UVN相机,使用了下面列出的各种教程,并阅读了关于四元数和轴角旋转的相关知识。但是我遇到了一个奇怪的错误,无法解决。
基本上,相机似乎一直正常工作,直到相机从+z旋转约45度为止,在这一点上,向上或向下倾斜相机似乎会围绕其目标轴倾斜相机,转动上向量。
当相机面对-z时,向上或向下倾斜会产生相反的错觉,向上倾斜会使相机向下倾斜,向下倾斜会使相机向上倾斜。
我已经看到其他实现建议使用非UVN系统,其中四元数累积成一个描述当前方向与某个任意起始角度之间差异的四元数。这听起来很棒,但是我似乎无法确定如何实现它,特别是从此转换为视图矩阵。
在SO的其他地方,我读到将旋转分成两个分别表示偏航和俯仰的四元数的方法,但我并不认为这是问题的原因,因为在这种情况下,如果我理解正确,应用这两个旋转的顺序并不重要。
相关源代码片段:
四元数操作
Quaternion<TValue> conjugate() const{
return Quaternion({ { -m_values[X], -m_values[Y], -m_values[Z], m_values[W] } });
};
Quaternion<TValue>& operator*=(const Quaternion<TValue>& rhs) {
TValue x, y, z, w;
w = rhs[W] * m_values[W] - rhs[X] * m_values[X] - rhs[Y] * m_values[Y] - rhs[Z] * m_values[Z];
x = rhs[W] * m_values[X] + rhs[X] * m_values[W] - rhs[Y] * m_values[Z] + rhs[Z] * m_values[Y];
y = rhs[W] * m_values[Y] + rhs[X] * m_values[Z] + rhs[Y] * m_values[W] - rhs[Z] * m_values[X];
z = rhs[W] * m_values[Z] - rhs[X] * m_values[Y] + rhs[Y] * m_values[X] + rhs[Z] * m_values[W];
m_values[X] = x;
m_values[Y] = y;
m_values[Z] = z;
m_values[W] = w;
return *this;
};
static Quaternion<TValue> rotation(Vector<3, TValue> axis, TValue angle){
float x, y, z, w;
TValue halfTheta = angle / 2.0f;
TValue sinHalfTheta = sin(halfTheta);
return Quaternion<TValue>({ { axis[X] * sinHalfTheta, axis[Y] * sinHalfTheta, axis[Z] * sinHalfTheta, cos(halfTheta) } });
};
向量旋转操作
Vector<dimensions, TValue> rotate(const Vector<3, TValue> axis, float angle){
Quaternion<TValue> R = Quaternion<TValue>::rotation(axis, angle);
Quaternion<TValue> V = (*this);
Vector<dimensions, TValue> result = R * V * R.conjugate();
return result;
}
相机方法
Camera::Camera(Vector<2, int> windowSize, float fov, float near, float far):
m_uvn(Matrix<4, float>::identity()),
m_translation(Matrix<4, float>::identity()),
m_ar(windowSize[Dimensions::X] / (float)windowSize[Dimensions::Y]),
m_fov(fov),
m_near(near),
m_far(far),
m_position(),
m_forward({ { 0, 0, 1 } }),
m_up({ { 0, 1, 0 } })
{
setViewMatrix(Matrix<4, float>::identity());
setProjectionMatrix(Matrix<4, float>::perspective(m_ar, m_near, m_far, m_fov));
};
Matrix<4, float> Camera::getVPMatrix() const{
return m_vp;
};
const Vector<3, float> Camera::globalY = Vector<3, float>({ { 0, 1, 0 } });
void Camera::setProjectionMatrix(const Matrix<4, float> p){
m_projection = p;
m_vp = m_projection * m_view;
};
void Camera::setViewMatrix(const Matrix<4, float> v){
m_view = v;
m_vp = m_projection * m_view;
};
void Camera::setTranslationMatrix(const Matrix<4, float> t){
m_translation = t;
setViewMatrix(m_uvn * m_translation);
}
void Camera::setPosition(Vector<3, float> position){
if (position != m_position){
m_position = position;
setTranslationMatrix(Matrix<4, float>::translation(-position));
}
};
void Camera::moveForward(float ammount){
setPosition(m_position + (m_forward * ammount));
}
void Camera::moveRight(float ammount){
setPosition(m_position + (getRight() * ammount));
}
void Camera::moveUp(float ammount){
setPosition(m_position + (m_up * ammount));
}
void Camera::setLookAt(Vector<3, float> target, Vector<3, float> up){
Vector<3, float> newUp = up.normalize();
Vector<3, float> newForward = target.normalize();
if (newUp != m_up || newForward != m_forward){
m_up = newUp;
m_forward = newForward;
Vector<3, float> newLeft = getLeft();
m_up = newLeft * m_forward;
m_uvn = generateUVN();
setViewMatrix(m_uvn * m_translation);
}
};
void Camera::rotateX(float angle){
Vector<3, float> hAxis = (globalY * m_forward).normalize();
m_forward = m_forward.rotate(hAxis, angle).normalize();
m_up = (m_forward * hAxis).normalize();
m_uvn = generateUVN();
setViewMatrix(m_translation * m_uvn);
}
void Camera::rotateY(float angle){
Vector<3, float> hAxis = (globalY * m_forward).normalize();
m_forward = m_forward.rotate(globalY, angle).normalize();
m_up = (m_forward * hAxis).normalize();
m_uvn = generateUVN();
setViewMatrix(m_translation * m_uvn);
}
Vector<3, float> Camera::getRight(){
return (m_forward * m_up).normalize();
}
Vector <3, float> Camera::getLeft(){
return (m_up * m_forward).normalize();
}
};
我猜问题要么出在我的四元数实现上,要么出在我使用它的方式上,但由于系统的复杂性,我似乎无法进一步确定问题。由于经历了奇怪的错误,我不确定我尝试实现相机的方式是否有问题?
教程
- https://www.youtube.com/watch?v=1Aw1PDu33PI
- http://www.gamedev.net/page/resources/_/technical/math-and-physics/a-simple-quaternion-based-camera-r1997
四元数/向量数学