c – 使用四元数的OpenGL立方体旋转

我一直在尝试使用在SDL全屏窗口中运行的OpenGL来旋转立方体.我设法用glRotatef()成功地做到了这一点,但是我经历了“万向节锁”以及与欧拉角相关的其他问题.想要改进我的程序,我研究了四元数.我编写了一个四元数类,遵循 this page上的指示,并尝试使用它来使用glMultMatrixf()旋转我的立方体,但是当旋转多于1个轴而角度不是90度的倍数时,立方体会变形.我检查了我的四元数到矩阵转换和我的四元数乘法代码,但我找不到任何错误.

这是问题的照片：

这是显示这些立方体的完整程序(需要SDL和OpenGL)

//==============================================================================
#include <cmath>

#include <SDL/SDL.h>
#include <SDL/SDL_opengl.h>

namespace game_lib
{
    struct vec3
    {
        vec3() : x(0),y(0),z(0) { }
        vec3(float x,float y,float z) : x(x),y(y),z(z) { }

        vec3 normalize();
        inline float lenSqr() { return x*x + y*y + z*z; }
        float len();

        inline vec3 operator+(vec3 v) { v.x += x; v.y += y; v.z += z; return v; }
        inline vec3 operator-(vec3 v) { v.x = x - v.x; v.y = y - v.y; v.z = z - v.z; return v; }
        inline vec3 operator*(float f) { return vec3(f*x,f*y,f*z); }
        inline vec3 operator/(float f) { return vec3(x/f,y/f,z/f); }


        bool operator==(vec3 v);

        float x,y,z;

        enum faces { FRONT,BACK,LEFT,RIGHT,TOP,BOTTOM };
    };
    inline vec3 operator*(float f,vec3 v) { return v*f; }

    struct quaternion
    {
        quaternion() : w(1),x(0),z(0) { }
        quaternion(float w,float x,float z) : w(w),x(x),z(z) { }
        quaternion(float angle,vec3 axis);

        quaternion normalize();
        inline float lenSqr() { return w*w + x*x + y*y + z*z; }
        float len();

        quaternion operator*(quaternion);

        float w,x,z;
    };

    void DrawGLCuboid(vec3 centre,vec3 dimensions,quaternion rotation,const vec3 colours[6]);
}

const int EPSILON = 0.001;

inline bool feq(float f1,float f2)
{
    const float diff = f1 - f2;
    return (diff > -EPSILON) && (diff < EPSILON);
}

//{=================== vec3 methods =================
game_lib::vec3 game_lib::vec3::normalize()
{
    const float lengthSqr = lenSqr();
    if (lengthSqr > 1-EPSILON*EPSILON and lengthSqr < 1+EPSILON*EPSILON) // Optimisation to not re-normalize a normalized vector
        return *this;
    const float length = std::sqrt(lengthSqr);
    return game_lib::vec3(x/length,y/length,z/length);
}

float game_lib::vec3::len() { return std::sqrt(lenSqr()); }

bool game_lib::vec3::operator==(vec3 v) { return feq(v.x,x) and feq(v.y,y) and feq(v.z,z); }
//}==================================================


//{================ quaternion methods ==============
game_lib::quaternion::quaternion(float angle,vec3 axis)
{
    const vec3 axisN = axis.normalize();
    const float sin_a_2 = std::sin(angle*M_PI/360);
    w = std::cos(angle*M_PI/360);
    x = axisN.x*sin_a_2;
    y = axisN.y*sin_a_2;
    z = axisN.z*sin_a_2;
}

game_lib::quaternion game_lib::quaternion::normalize()
{
    const float lengthSqr = lenSqr();
    if (lengthSqr > 1-EPSILON*EPSILON and lengthSqr < 1+EPSILON*EPSILON) // Optimisation to not re-normalize a normalized quaternion
        return *this;
    const float length = std::sqrt(lengthSqr);
    return game_lib::quaternion(w/length,x/length,z/length);
}

float game_lib::quaternion::len() { return std::sqrt(lenSqr()); }

game_lib::quaternion game_lib::quaternion::operator*(game_lib::quaternion q)
{
    return game_lib::quaternion(w*q.w - x*q.x - y*q.y - z*q.z,w*q.x + x*q.w + y*q.z - z*q.y,w*q.y - x*q.z + y*q.w + z*q.x,w*q.z + x*q.y - y*q.x + z*q.w);
}
//}==================================================


void game_lib::DrawGLCuboid(vec3 cen,vec3 dim,quaternion rot,const vec3 col[6])
{
    glPushMatrix();
    glTranslatef(cen.x,cen.y,cen.z);
    vec3 dim_2 = 1/2*dim;
    const quaternion r_norm = rot.normalize();

    // Quaternion to matrix
    const float x_x = r_norm.x*r_norm.x,y_y = r_norm.y*r_norm.y,z_z = r_norm.z*r_norm.z;
    const float w_x = r_norm.w*r_norm.x,w_y = r_norm.w*r_norm.y,w_z = r_norm.w*r_norm.z;
    const float x_y = r_norm.x*r_norm.y,x_z = r_norm.x*r_norm.z,y_z = r_norm.y*r_norm.z;

    GLfloat matrix[16];

    // Column 1                  // Column 2                  // Column 3                  // Column 4
    matrix[0] = 1-2*(y_y+z_z);   matrix[4] = 2*(x_y-w_z);     matrix[8] = 2*(x_z+w_y);     matrix[12] = 0;
    matrix[1] = 2*(x_y+w_z);     matrix[5] = 1-2*(x_x+z_z);   matrix[9] = 2*(y_z+w_x);     matrix[13] = 0;
    matrix[2] = 2*(x_z-w_y);     matrix[6] = 2*(y_z-w_x);     matrix[10] = 1-2*(x_x+y_y);  matrix[14] = 0;
    matrix[3] = 0;               matrix[7] = 0;               matrix[11] = 0;              matrix[15] = 1;

    /* From http://www.cprogramming.com/tutorial/3d/quaternions.html
    1-2y2-2z2   2xy-2wz     2xz+2wy     0

    2xy+2wz     1-2x2-2z2   2yz+2wx     0

    2xz-2wy     2yz-2wx     1-2x2-2y2   0

    0           0           0           1
    */

    glMultMatrixf(matrix);

    glBegin(GL_QUADS);
        int i = vec3::FRONT;
        glColor3f(col[i].x,col[i].y,col[i].z);

        glVertex3f(-1,1,1);
        glVertex3f(1,-1,1);
        glVertex3f(-1,1);


        i = vec3::BACK;
        glColor3f(col[i].x,-1);
        glVertex3f(1,-1);
        glVertex3f(-1,-1);


        i = vec3::LEFT;
        glColor3f(col[i].x,-1);


        i = vec3::RIGHT;
        glColor3f(col[i].x,col[i].z);

        glVertex3f(1,-1);


        i = vec3::BOTTOM;
        glColor3f(col[i].x,-1);


        i = vec3::TOP;
        glColor3f(col[i].x,-1);

        glColor3f(1,1);

        // Following three quads are axes to help determine rotational correctness...
        // x-axis
        glVertex3f(-2,0.05,0.05);
        glVertex3f(2,-0.05,-0.05);
        glVertex3f(-2,-0.05);

        // y-axis
        glVertex3f(0.05,-2,0.05);
        glVertex3f(0.05,2,0.05);
        glVertex3f(-0.05,-0.05);
        glVertex3f(-0.05,-0.05);

        // z-axis
        glVertex3f(0.05,-2);
        glVertex3f(0.05,2);
        glVertex3f(-0.05,-2);
    glEnd();
    glPopMatrix();
}

using namespace game_lib;

struct SDL_Surface;
union SDL_Event;

class CApp {
    private:
        bool m_running,m_init;
        SDL_Surface* m_screen;
        float depth;

    public:
        CApp();
        ~CApp();
        bool init();
        int execute();
        void cleanup();

    private:
        //void processEvent(SDL_Event* Event); // Usually I have this,but it's big and irrelevant (
        void render();
};


//==============================================================================
CApp::CApp()
: m_running(true),m_init(false),m_screen(NULL),depth(-6) { }

CApp::~CApp()
{
    if (m_init) cleanup();
}

//------------------------------------------------------------------------------

bool CApp::init()
{
    if(SDL_Init(SDL_INIT_EVERYTHING) < 0)
        return false;


    SDL_GL_SetAttribute(SDL_GL_DOUBLEBUFFER,1);

    SDL_GL_SetAttribute(SDL_GL_RED_SIZE,8);
    SDL_GL_SetAttribute(SDL_GL_GREEN_SIZE,8);
    SDL_GL_SetAttribute(SDL_GL_BLUE_SIZE,8);
    SDL_GL_SetAttribute(SDL_GL_ALPHA_SIZE,8);

    SDL_GL_SetAttribute(SDL_GL_DEPTH_SIZE,16);
    SDL_GL_SetAttribute(SDL_GL_BUFFER_SIZE,32);

    SDL_GL_SetAttribute(SDL_GL_ACCUM_RED_SIZE,8);
    SDL_GL_SetAttribute(SDL_GL_ACCUM_GREEN_SIZE,8);
    SDL_GL_SetAttribute(SDL_GL_ACCUM_BLUE_SIZE,8);
    SDL_GL_SetAttribute(SDL_GL_ACCUM_ALPHA_SIZE,8);

    SDL_GL_SetAttribute(SDL_GL_MULTISAMPLEBUFFERS,1);
    SDL_GL_SetAttribute(SDL_GL_MULTISAMPLESAMPLES,2);

    const SDL_VideoInfo* inf = SDL_GetVideoInfo();

    if((m_screen = SDL_SetVideoMode(inf->current_w,inf->current_h,SDL_OPENGL | SDL_FULLSCREEN)) == NULL)
        return false;

    glClearColor(0,0);

    glClearDepth(1);
    glEnable(GL_DEPTH_TEST);
    glDepthFunc(GL_LEQUAL);

    glViewport(0,inf->current_w,inf->current_h);

    glMatrixMode(GL_PROJECTION); // Camera space
    glLoadIdentity();

    gluPerspective(45.0f,1024.0f/600.0f,0.1f,100.0f);

    glEnable(GL_TEXTURE_2D);
    glMatrixMode(GL_MODELVIEW); // Model space
    glLoadIdentity();

    m_init = true;
    return true;
}

int CApp::execute()
{
    if(init() == false)
        return -1;
    SDL_Event event;
    while(m_running)
    {
        //while(SDL_PollEvent(&event))
            // process events removed to save space
        render();
        SDL_Delay(10);
    }
    cleanup();
    return 0;
}

void CApp::cleanup()
{
    if (m_screen)
    {
        SDL_FreeSurface(m_screen);
        m_screen = NULL;
    }
    SDL_Quit();
    m_init = false;
}

void CApp::render()
{
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
    glLoadIdentity();

    glTranslatef(0.0f,0.0f,depth);

    //glRotatef(63,0); // How I used to do rotation
    //glRotatef(47,0);

    const vec3 c1colours[] = {vec3(1,0),vec3(0,vec3(1,0.2,1),0.5,1)};
    const vec3 c2colours[] = {vec3(1,vec3(0.5,0)};

    // New rotation method,but doesn't work...
    const quaternion c1Rotation = quaternion(63,0)) * quaternion(47,0));

    DrawGLCuboid(vec3(-2,-2),vec3(2,2),c1Rotation,c1colours);
    DrawGLCuboid(vec3(2.5,0.3,-1.2),quaternion(72,1)),c2colours);

    SDL_GL_SwapBuffers();
}




int main(int argc,char* argv[])
{
    CApp theApp;
    return theApp.execute();
}

matrix[1] = 2*(x_y+w_z);     matrix[5] = 1-2*(x_x+z_z);   matrix[9] = 2*(y_z-w_x);     matrix[13] = 0;
matrix[2] = 2*(x_z-w_y);     matrix[6] = 2*(y_z+w_x);     matrix[10] = 1-2*(x_x+y_y);  matrix[14] = 0;