据我理解，
gluLookAt(
eye_x, eye_y, eye_z,
center_x, center_y, center_z,
up_x, up_y, up_z
);
等同于：
glRotatef(B, 0.0, 0.0, 1.0);
glRotatef(A, wx, wy, wz);
glTranslatef(-eye_x, -eye_y, -eye_z);
但是当我打印出ModelView矩阵时，调用glTranslatef()似乎无法正常工作。以下是代码片段：
#include <stdlib.h>
#include <stdio.h>
#include <GL/glut.h>
#include <iomanip>
#include <iostream>
#include <string>
using namespace std;
static const int Rx = 0;
static const int Ry = 1;
static const int Rz = 2;
static const int Ux = 4;
static const int Uy = 5;
static const int Uz = 6;
static const int Ax = 8;
static const int Ay = 9;
static const int Az = 10;
static const int Tx = 12;
static const int Ty = 13;
static const int Tz = 14;
void init() {
glClearColor(0.0, 0.0, 0.0, 0.0);
glEnable(GL_DEPTH_TEST);
glShadeModel(GL_SMOOTH);
glEnable(GL_LIGHTING);
glEnable(GL_LIGHT0);
GLfloat lmodel_ambient[] = { 0.8, 0.0, 0.0, 0.0 };
glLightModelfv(GL_LIGHT_MODEL_AMBIENT, lmodel_ambient);
}
void displayModelviewMatrix(float MV[16]) {
int SPACING = 12;
cout << left;
cout << "\tMODELVIEW MATRIX\n";
cout << "--------------------------------------------------" << endl;
cout << setw(SPACING) << "R" << setw(SPACING) << "U" << setw(SPACING) << "A" << setw(SPACING) << "T" << endl;
cout << "--------------------------------------------------" << endl;
cout << setw(SPACING) << MV[Rx] << setw(SPACING) << MV[Ux] << setw(SPACING) << MV[Ax] << setw(SPACING) << MV[Tx] << endl;
cout << setw(SPACING) << MV[Ry] << setw(SPACING) << MV[Uy] << setw(SPACING) << MV[Ay] << setw(SPACING) << MV[Ty] << endl;
cout << setw(SPACING) << MV[Rz] << setw(SPACING) << MV[Uz] << setw(SPACING) << MV[Az] << setw(SPACING) << MV[Tz] << endl;
cout << setw(SPACING) << MV[3] << setw(SPACING) << MV[7] << setw(SPACING) << MV[11] << setw(SPACING) << MV[15] << endl;
cout << "--------------------------------------------------" << endl;
cout << endl;
}
void reshape(int w, int h) {
float ratio = static_cast<float>(w)/h;
glViewport(0, 0, w, h);
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
gluPerspective(45.0, ratio, 1.0, 425.0);
}
void draw() {
float m[16];
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
glMatrixMode(GL_MODELVIEW);
glLoadIdentity();
glGetFloatv(GL_MODELVIEW_MATRIX, m);
gluLookAt(
300.0f, 0.0f, 0.0f,
0.0f, 0.0f, 0.0f,
0.0f, 1.0f, 0.0f
);
glColor3f(1.0, 0.0, 0.0);
glutSolidCube(100.0);
glGetFloatv(GL_MODELVIEW_MATRIX, m);
displayModelviewMatrix(m);
glutSwapBuffers();
}
int main(int argc, char** argv) {
glutInit(&argc, argv);
glutInitDisplayMode(GLUT_DOUBLE | GLUT_RGB | GLUT_DEPTH);
glutInitWindowSize(400, 400);
glutInitWindowPosition(100, 100);
glutCreateWindow("Demo");
glutReshapeFunc(reshape);
glutDisplayFunc(draw);
init();
glutMainLoop();
return 0;
}
无论我使用什么值作为
eye向量：300, 0, 0 或者 0, 300, 0 或者 0, 0, 300平移向量都是相同的，这没有任何意义，因为代码顺序是反向的，所以应该先运行
glTranslatef，然后是2次旋转。此外，旋转矩阵与平移列（在ModelView矩阵中）完全独立，那么是什么导致了这种奇怪的行为？这里是当eye向量为(0.0f, 300.0f, 0.0f)时的输出。 MODELVIEW MATRIX
--------------------------------------------------
R U A T
--------------------------------------------------
0 0 0 0
0 0 0 0
0 1 0 -300
0 0 0 1
--------------------------------------------------
我希望您能够解释一下，为什么
T 列应该是 (0, -300, 0)！是否有人可以帮助我解释一下？来自 http://www.mesa3d.org 的
gluLookAt 实现。void GLAPIENTRY
gluLookAt(GLdouble eyex, GLdouble eyey, GLdouble eyez, GLdouble centerx,
GLdouble centery, GLdouble centerz, GLdouble upx, GLdouble upy,
GLdouble upz)
{
float forward[3], side[3], up[3];
GLfloat m[4][4];
forward[0] = centerx - eyex;
forward[1] = centery - eyey;
forward[2] = centerz - eyez;
up[0] = upx;
up[1] = upy;
up[2] = upz;
normalize(forward);
/* Side = forward x up */
cross(forward, up, side);
normalize(side);
/* Recompute up as: up = side x forward */
cross(side, forward, up);
__gluMakeIdentityf(&m[0][0]);
m[0][0] = side[0];
m[1][0] = side[1];
m[2][0] = side[2];
m[0][1] = up[0];
m[1][1] = up[1];
m[2][1] = up[2];
m[0][2] = -forward[0];
m[1][2] = -forward[1];
m[2][2] = -forward[2];
glMultMatrixf(&m[0][0]);
glTranslated(-eyex, -eyey, -eyez);
}
glTranslated(-eyex, -eyey, -eyez)，所以我的假设必须是正确的。forward、up、side向量只用于左上角的3x3矩阵，所以我不明白它们如何影响平移向量？ - roxrook