opengl的坐标指向问题，glmatrixmode(gl_modeview)对其有何影响？

[woshiniaoshi]

画了一个三维坐标轴，带箭头，和一个正空间的立方体，我怎么觉得它好像z轴是指向屏幕里面的，源码如下：

//最初的疑惑即是来自于此程序，一个立方体x转-30，y转-30之后，有深度检测
//可以看到z是指向里面的


//#include <windows.h>
#include <gl/glut.h>

static float angle_x = 0, angle_y=-10,angle_z=0;

void zuobiao() //画出坐标线,正方向有箭头
{

glBegin(GL_LINES);
glColor3f(1.0,0.0,0.0);
glVertex3f(-0.25f,0.0f,0.0f); //x 红
glVertex3f(0.8f,0.0f,0.0f);

glColor3f(0.8f,0.5f,0.9f);
glVertex3f(0.0f,-0.25f,0.0f); //y
glVertex3f(0.0f,0.8f,0.0f);

glColor3f(1.0,1.0,1.0);
glVertex3f(0.0f,0.0f,-0.5f); //z 白
glVertex3f(0.0f,0.0f,0.8f);
glEnd();


glBegin(GL_TRIANGLES);

glVertex3f(-0.1,-0.1,0.8);//z
glVertex3f(0.1,0.1,0.8);
glVertex3f(0.0,0.0,1.0);

glColor3f(1.0,0.0,0.0);//x
glVertex3f(0.8,0.1,0.1);
glVertex3f(0.8,-0.1,-0.1);
glVertex3f(1.0,0.0,0.0);
glColor3f(0.8f,0.5f,0.9f);//y
glVertex3f(-0.1,0.8,0.1);
glVertex3f(0.1,0.8,-0.1);
glVertex3f(0.0,1.0,0.0);

glEnd();

}


void myplay() //6面都有的立方体
{


glEnable(GL_DEPTH_TEST);
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
/* gluPerspective(60.0f,1,0.1f,100.0f);
glMatrixMode(GL_MODELVIEW);
glLoadIdentity();
glTranslatef(0,0,-2);

*/

glRotatef(-30,0,1,0); // 面朝y的正方向，绕y轴逆时针旋转 -30
glRotatef(-30,1,0,0);//面朝x的正方向，绕x轴逆时针旋转 -30
zuobiao(); //自己定义的一个画出3根坐标线的函数，在正方向有箭头
glBegin(GL_POLYGON); //
glColor3f(1.0,0.0,0.0);
glVertex3f(0.0f,0.0f,0.0f);
glVertex3f(0.0f,0.5f,0.0f);
glVertex3f(0.5f,0.5f,0.0f);
glVertex3f(0.5f,0.0f,0.0f);
glEnd();
glBegin(GL_POLYGON);
glColor3f(1.0f,1.0,0.0);
glVertex3f(0.0f,0.0f,0.0f);
glVertex3f(0.0f,0.5f,0.0f);
glVertex3f(0.0f,0.5f,0.5f);
glVertex3f(0.0f,0.0f,0.5f);
glEnd();

glBegin(GL_POLYGON);
glColor3f(1.0,0.0,1.0);
glVertex3f(0.0f,0.0f,0.0f);
glVertex3f(0.0f,0.0f,0.5f);
glColor3f(1.0,0.0,0.0);
glVertex3f(0.5f,0.0f,0.5f);
glColor3f(0.0,1.0,0.0);
glVertex3f(0.5f,0.0f,0.0f);
glEnd();

glBegin(GL_POLYGON);
glColor3f(0.0,1.0,0.0);
glVertex3f(0.0f,0.5f,0.0f);
glVertex3f(0.5f,0.5f,0.0f);
glVertex3f(0.5f,0.5f,0.5f);
glVertex3f(0.0f,0.5f,0.5f);
glEnd();

glBegin(GL_POLYGON);
glColor3f(0.0,1.0,1.0);
glVertex3f(0.5f,0.5f,0.0f);
glVertex3f(0.5f,0.5f,0.5f);
glVertex3f(0.5f,0.0f,0.5f);
glVertex3f(0.5f,0.0f,0.0f);
glEnd();

glBegin(GL_POLYGON);
glColor3f(0.4,1.0,0.6);
glVertex3f(0.5f,0.5f,0.5f);
glVertex3f(0.5f,0.0f,0.5f);
glVertex3f(0.0f,0.0f,0.5f);
glVertex3f(0.0f,0.5f,0.5f);
glEnd();

glFlush();
}

int main(int argc, char *argv[])

{
glutInit(&argc, argv);
glutInitDisplayMode(GLUT_RGB | GLUT_SINGLE);
glutInitWindowPosition(300,200);
glutInitWindowSize(400,400);
glutCreateWindow("立方体");
glutDisplayFunc(&myplay);

glutMainLoop();
return 0;
}

如果加上myplay（）中的注释掉的代码，就可以实现投影空间，也就是有近大远小的效果，可是这时候我发现旋转的角度又不对了，不再是绕轴逆时钟旋转了，难道此时旋转的是看物体的眼睛而不再是物体了？
望各位赐教，祝各位牛年大吉！

[woshiniaoshi]

C:\Documents and Settings\Administrator\桌面\立方体.bmp

[woshiniaoshi]

[img=C:\Documents and Settings\Administrator\桌面\立方体.bmp]C:\Documents and Settings\Administrator\桌面\立方体.bmp[/img]

[woshiniaoshi]

谢谢您，我似乎理解一点了，就是如果设置了glMatrixMode（GL_MODEVIEW）那接下来的操作就是对眼睛的操作了，可以这样理解吗
但是我还是不明白第一个问题，我的源码运行为什么可以看到z轴是指向里面的？
源码设置的是glMatrixMode(GL_PROJECTION); 旋转的角度方向也是对的
为什么z轴向里？

我想把我的图贴出来但是不知道怎么贴，能麻烦您把我的源码运行一下，指点一下吗

[zzz822163]

glMatrixMode():指定哪一个矩阵是当前矩阵

C语言描述

void glMatrixMode(GLenum mode)

参数

mode指定哪一个矩阵堆栈是下一个矩阵操作的目标，可选值:GL_MODELVIEW、GL_PROJECTION、GL_TEXTURE.

说明

glMatrixMode设置当前矩阵模式：

GL_MODEVIEW，对模型视景矩阵堆栈应用随后的矩阵操作。

GL_PROJECTION，对投影矩阵应用随后的矩阵操作。

GLTEXTURE，对纹理矩阵堆栈应用随后的矩阵操作。
=============================
其实GL_MODEVIEW和GL_PROJECTION只是相对的概念,移动物体和移动眼睛都可以达到相同的目的,

[zzz822163]

眼睛默认是朝向Z轴负方向的,你需要用gluLookAt()来设置一下眼睛

[wxfasdic_12]

你好，我想问一下，怎么让坐标系不动，而绘制的物体转动呢？

[IONPhantom]

[Quote=引用 4 楼 woshiniaoshi 的回复:]
谢谢您，我似乎理解一点了，就是如果设置了glMatrixMode（GL_MODEVIEW）那接下来的操作就是对眼睛的操作了，可以这样理解吗
但是我还是不明白第一个问题，我的源码运行为什么可以看到z轴是指向里面的？
源码设置的是glMatrixMode(GL_PROJECTION); 旋转的角度方向也是对的
为什么z轴向里？

我想把我的图贴出来但是不知道怎么贴，能麻烦您把我的源码运行一下，指点一下吗
[/Quote]
GL_MODEVIEW和GL_PROJECTION其实都是在设置摄像机的属性,之所以设置它俩能"改变"物体的位置和朝向是因为你要使用摄像机来观察物体,对于物体来说改变View和Proj Matrix对逻辑意义上的物体并没有关系.

Z轴朝向也是同一个问题,只要你的三个轴的朝向分别是 X(1,0,0) Y(0,1,0) Z(0,0,1) 那么Z轴的方向就已经固定了,它本质的朝向不会因为改变了,但是它看起来会发生改变是也是因为摄像机的问题,摄像机的位置改变了造成观察的时候物体(坐标轴也是物体)改变了