OpenGL gluLookAt()没有按预期工作

Question

我正在OpenGL中的天空盒内制作一个过山车,并且没有太多关于它的功能或计算机图形的背景,它被证明是非常困难的.我使用Catmull-Rom样条插值绘制了一个过山车,并用glVertex3f绘制了每个点.现在我想update()每50ms 调用一次功能来将摄像机移动到轨道上.gluLookAt()产生奇怪的结果,要么从屏幕上删除轨道,产生黑屏等等.我想我需要移动一些矩阵函数,但我不知道在哪里放置每个.到目前为止,这是我的代码:

int main(int argc, char** argc)
{
    // ... load track, etc ...

    // Init currpos, nextpos, iter, up
    currpos = Vec3f(0, 0, 0);
    nextpos = currpos;
    iter = 0;
    up = Vec3f(0, 1, 0);

    deque<Vec3f> points;
    Vec3f newpt;

    // Loop through the points and interpolate 
    for (pointVectorIter pv = g_Track.points().begin(); pv != g_Track.points().end(); pv++)
    {
        Vec3f curr(*pv);            // Initialize the current point and a new point (to be drawn)
        points.push_back(curr);     // Push the current point onto the stack
        allpoints.push_back(curr);  // Add current point to the total stack

        if (points.size() == 4) // Check if there are 4 points in the stack, if so interpolate
        {
            for (float u = 0.0f; u < 1.0f; u += 0.01f)
            {
                newpt = interpolate(points[0], points[1], points[2], points[3], u);
                glColor3f(1, 1, 1);
                glVertex3f(newpt.x(), newpt.y(), newpt.z());

                allpoints.push_back(newpt);
            }

            points.pop_front();
        }
    }

    // glutInit, InitGL(), etc...
}

void InitGL(GLvoid)
{
    glEnable(GL_DEPTH_TEST);
    glDepthFunc(GL_LEQUAL);
    glMatrixMode(GL_PROJECTION);
    glLoadIdentity();
    gluPerspective(100.0, (GLfloat)WINDOW_WIDTH / (GLfloat)WINDOW_HEIGHT, .0001, 999999);
    glMatrixMode(GL_MODELVIEW);
    glClearColor(0.0f, 0.0f, 0.0f, 0.5f);
}

void display (void)
{
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
    glMatrixMode(GL_MODELVIEW);
    glLoadIdentity();
    gluLookAt(currpos.x(), currpos.y(), currpos.z(), nextpos.x(), nextpos.y(), nextpos.z(), up.x(), up.y(), up.z());

    glPushMatrix();
    glEnable(GL_TEXTURE_2D); // Enable texturing from now on

    /* draw skybox, this was from previous assignment and renders correctly */

    glPopMatrix();

    // now draw rollercoaster ...

    glPushMatrix();
    glBegin(GL_LINE_STRIP);

    deque<Vec3f> points;
    Vec3f newpt;

    for each (Vec3f pt in allpoints)
    {
        glColor3f(1, 1, 1);
        glVertex3f(pt.x(), pt.y(), pt.z());
    }

    glutTimerFunc(50, update, 1);
    glEnd();
    glPopMatrix();

    // Swap buffers, so one we just drew is displayed
    glutSwapBuffers();
}

void update(int a)
{
    if (iter < allpoints.size())
    {
        currpos = allpoints[iter];
        nextpos = allpoints[iter + 1];

        gaze = nextpos - currpos;
        gaze.Normalize();

        Vec3f::Cross3(binorm, gaze, up);
        binorm.Normalize();

        Vec3f::Cross3(up, binorm, gaze);
        up.Normalize();

        glutPostRedisplay();
    }

    iter++;
}

我的想法是保持一个allpoints包含样条控制点和插值点的全局双端队列.一旦完成,我update()每50ms 调用一次,并沿着每个点移动相机allpoints.在该项目的先前版本中,我可以看到正在正确绘制过山车.这gluLookAt()似乎并不像我想要的那样.使用上面的代码,程序开始时相机用过山车的一部分观看天空盒的一侧,然后当update()调用时,过山车消失但相机不移动.我一直在搞乱我放置OpenGL矩阵函数的位置,并且根据它们有时update()会导致空白屏幕.

Answer 1

除了缺少glPopMatrix(用户971377已经发现)之外,您可以调用glLoadIdentity绘图例程,这当然会覆盖您在update方法(使用gluLookAt)中对模型视图矩阵所做的任何更改.

永远记住:gluLookAt,glOrtho,gluPerspective,glTranslate,glRotate,和所有其他矩阵和转换功能始终是头等元素(通过改变上运行glPush/PopMatrix当前选定的矩阵堆栈(通过改变)glMatrixMode).它们总是将当前矩阵相乘,而不是替换它.所以喜欢gluPerspective,你应该在打电话glLoadIdentity前打电话gluLookAt.并且整个摄像机的更改应该在渲染例程中完成,而不是更新例程.

update您应该更改摄像机所依赖的变量,并在方法中设置摄像机(gluLookAt在模型视图矩阵上),而不是进行任何GL变换display.为了演示这些函数的标准用法,您的代码应该类似于:

void display()
{
    <general state setup (glClear, ...)>

    glMatrixMode(GL_MODELVIEW);
    glLoadIdentity();
    glLookAt(camera);     //view transformation (camera)

    //object 1
    glPushMatrix();       //save modelview
    glTranslate/glRotate/glScale;        //local model transformations
    <draw object 1>
    glPopMatrix();
    ...
    //object n
    glPushMatrix();       //save modelview
    glTranslate/glRotate/glScale;        //local model transformations
    <draw object n>
    glPopMatrix();

    gluSwapBuffers();
}

void update()
{
    camera = ...;
}

}