gluLookAt(GLdouble eyeX, GLdouble eyeY, GLdouble eyeZ, GLdouble centerX, GLdouble centerY, GLdouble centerZ, GLdouble upX, GLdouble upY, GLdouble upZ);
参数解释:
视点:(eyeX,eyeY,eyeZ)
观察点:(centerX,centerY,centerZ)
V(向上)向量 :(upX,upY,upZ)
函数原理:
步骤:
(1)世界坐标系中选中一点eye(eyeX,eyeY,eyeZ)作为视点,则定义z轴为:(centerX-eyeX,centerY-eyeY,centerZ-eyeZ),并归一化;
(2)再指定定义y方向的观察向上向量V(upX,upY,upZ),注意:此时的V与z未必垂直,然后将归一化后的z与V进行一次叉乘,得到x轴,也进行归一化;
(3)至此,视点的坐标系只剩下y轴没有确定,同理,只需将归一化后z轴与x轴进行叉乘运算便得到了y轴,最后再将y轴进行归一化;
综上:其实gluLookat()函数的实现就是确定视点的坐标系的过程,也即求世界坐标系到观察坐标系的一个4*4的变换。
#include
#include
#include
#include
using namespace std;
struct point
{
GLdouble x, y, z;
point()
{
x = y = z = 0;
}
point(GLdouble _x, GLdouble _y, GLdouble _z)
{
x = _x;
y = _y;
z = _z;
}
};
typedef point Vector;
void Normalize(Vector &V)
{
GLdouble tmp = sqrt(V.x*V.x + V.y*V.y + V.z*V.z);
V.x = V.x / tmp;
V.y = V.y / tmp;
V.z = V.z / tmp;
}
Vector Cross(Vector a, Vector b)//
{
return Vector(a.y*b.z - a.z*b.y, a.z*b.x - a.x*b.z, a.x*b.y - a.y*b.x);
}
//视点、参考点、向上向量V
void MyLookAt(GLdouble eyeX, GLdouble eyeY, GLdouble eyeZ, GLdouble centerX, GLdouble centerY, GLdouble centerZ, GLdouble upX, GLdouble upY, GLdouble upZ)
{
GLdouble Mat[16];
memset(Mat, 0, sizeof(Mat));//内存空间初始化(用来对一段内存空间全部设置为某个字符,一般用在对定义的字符串进行初始化为' '或'/0')
Mat[15] = 1;
Vector forward(centerX - eyeX, centerY - eyeY, centerZ - eyeZ);//正Z轴方向
Vector up(upX, upY, upZ);//向上向量
Normalize(forward);//归一化
Vector side = Cross(forward, up);//x方向
Normalize(side);
up = Cross(side, forward);//y方向
Mat[0] = side.x;
Mat[4] = side.y;
Mat[8] = side.z;
Mat[1] = up.x;
Mat[5] = up.y;
Mat[9] = up.z;
Mat[2] = -forward.x;
Mat[6] = -forward.y;
Mat[10] = -forward.z;
cout << Mat[10] << " ";
cout << endl;
glLoadMatrixd(Mat);
glTranslated(-eyeX, -eyeY, -eyeZ);
}
void init(void)
{
glClearColor(0.0, 0.0, 0.0, 0.0); //背景黑色
}
void display(void)
{
glClear(GL_COLOR_BUFFER_BIT);
glColor3f(1.0, 1.0, 1.0); //画笔白色
glLoadIdentity(); //加载单位矩阵
// gluLookAt(0, 0, 10.0, 0.0, 0.0, 0.0, 0.0, 1.0, 0.0);
MyLookAt(0, 0, 10.0, 0.0, 0.0, 0.0, 0.0, 1.0, 0.0);
glutWireTeapot(2);
glutSwapBuffers();
}
void reshape(int w, int h)
{
glViewport(0, 0, (GLsizei)w, (GLsizei)h);
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
gluPerspective(60.0, (GLfloat)w / (GLfloat)h, 1.0, 20.0);
glMatrixMode(GL_MODELVIEW);
glLoadIdentity();
}
int main(int argc, char** argv)
{
glutInit(&argc, argv);
glutInitDisplayMode(GLUT_DOUBLE | GLUT_RGB);
glutInitWindowSize(800, 600);
glutInitWindowPosition(100, 100);
glutCreateWindow(argv[0]);
init();
glutDisplayFunc(display);
glutReshapeFunc(reshape);
glutMainLoop();
return 0;
}
到这里说完了,第一次发博客文章,文字解释可能逻辑性不是太强,但只要开始就是好的,也希望自己能越写越好!