为什么OpenGL纹理出来后前面板总是透视？解决方法

为什么OpenGL纹理出来后前面板总是透视？
下面是我做的一个纹理的3d箱子模型程序，可是运行后前面板总是透视，移动到箱子里面后看到的就不是透视的。很奇怪，请各位仁兄指点迷津。
 
#include "gl/glut.h"
#include "gl/glaux.h"

BOOL light=TRUE;
BOOL lp,fp;

GLfloat xrot,yrot;
GLfloat xspeed,yspeed;

GLfloat z=-5.0f;
GLfloat LightAmbient[]={0.8,0.8,0.8,1.0};
GLfloat LightDiffuse[]={1.0,1.0,1.0,1.0};

GLfloat LightPosition[]={0.0,0.0,2.0};
GLuint filter;
GLuint Texture[3];

void LoadGLTextures()
{//载入位图并转换成纹理
AUX_RGBImageRec *TextureImage[1];
memset(TextureImage,0,sizeof(void *)*1); // 将指针设为 NULL
TextureImage[0]=auxDIBImageLoad("DATA/Crate.bmp");
glGenTextures(3,&Texture[0]);

//生成Nearset纹理
glBindTexture(GL_TEXTURE_2D,Texture[0]);
glTexImage2D(GL_TEXTURE_2D,0,3,TextureImage[0]->sizeX,TextureImage[0]->sizeY,0,GL_RGB,GL_UNSIGNED_BYTE,TextureImage[0]->data);
glTexParameteri(GL_TEXTURE_2D,GL_TEXTURE_MAG_FILTER,GL_NEAREST);
glTexParameteri(GL_TEXTURE_2D,GL_TEXTURE_MIN_FILTER,GL_NEAREST);
//生成线性纹理
glBindTexture(GL_TEXTURE_2D,Texture[1]);
glTexImage2D(GL_TEXTURE_2D,0,3,TextureImage[0]->sizeX,TextureImage[0]->sizeY,0,GL_RGB,GL_UNSIGNED_BYTE,TextureImage[0]->data);

glTexParameteri(GL_TEXTURE_2D,GL_TEXTURE_MAG_FILTER,GL_LINEAR);
glTexParameteri(GL_TEXTURE_2D,GL_TEXTURE_MIN_FILTER,GL_LINEAR);
//Mipmapped纹理
glBindTexture(GL_TEXTURE_2D,Texture[2]);

//建立二维多重映射 
gluBuild2DMipmaps(GL_TEXTURE_2D,3,TextureImage[0]->sizeX,TextureImage[0]->sizeY,GL_RGB,GL_UNSIGNED_BYTE,TextureImage[0]->data);
glTexParameteri(GL_TEXTURE_2D,GL_TEXTURE_MAG_FILTER,GL_LINEAR);
glTexParameteri(GL_TEXTURE_2D,GL_TEXTURE_MIN_FILTER,GL_LINEAR);

free(TextureImage[0]->data);
free(TextureImage[0]);


}

void RenderScene(void)
{
glClear(GL_COLOR_BUFFER_BIT|GL_DEPTH_BUFFER_BIT);
glLoadIdentity();

glTranslatef(0.0f,0.0f,z); //为什么不加这句就不显示模型？
//因为当前坐标是（0，0，0）我认为在屏幕上移动就跑到屏幕外边了
glRotatef(xrot,1.0,0.0,0.0);
glRotatef(yrot,0.0,1.0,0.0);

glBindTexture(GL_TEXTURE_2D,Texture[filter]);

glBegin(GL_QUADS);
// 前面
glNormal3f( 0.0f, 0.0f, 1.0f);
glTexCoord2f(0.0f, 0.0f); glVertex3f(-1.0f, -1.0f, 1.0f);
glTexCoord2f(1.0f, 0.0f); glVertex3f( 1.0f, -1.0f, 1.0f);
glTexCoord2f(1.0f, 1.0f); glVertex3f( 1.0f, 1.0f, 1.0f);
glTexCoord2f(0.0f, 1.0f); glVertex3f(-1.0f, 1.0f, 1.0f);
// 后面
glNormal3f( 0.0f, 0.0f,-1.0f);
glTexCoord2f(1.0f, 0.0f); glVertex3f(-1.0f, -1.0f, -1.0f);
glTexCoord2f(1.0f, 1.0f); glVertex3f(-1.0f, 1.0f, -1.0f);
glTexCoord2f(0.0f, 1.0f); glVertex3f( 1.0f, 1.0f, -1.0f);
glTexCoord2f(0.0f, 0.0f); glVertex3f( 1.0f, -1.0f, -1.0f);
// Top Face
glNormal3f( 0.0f, 1.0f, 0.0f);
glTexCoord2f(0.0f, 1.0f); glVertex3f(-1.0f, 1.0f, -1.0f);
glTexCoord2f(0.0f, 0.0f); glVertex3f(-1.0f, 1.0f, 1.0f);
glTexCoord2f(1.0f, 0.0f); glVertex3f( 1.0f, 1.0f, 1.0f);
glTexCoord2f(1.0f, 1.0f); glVertex3f( 1.0f, 1.0f, -1.0f);
// 地面
glNormal3f( 0.0f,-1.0f, 0.0f);
glTexCoord2f(1.0f, 1.0f); glVertex3f(-1.0f, -1.0f, -1.0f);
glTexCoord2f(0.0f, 1.0f); glVertex3f( 1.0f, -1.0f, -1.0f);
glTexCoord2f(0.0f, 0.0f); glVertex3f( 1.0f, -1.0f, 1.0f);
glTexCoord2f(1.0f, 0.0f); glVertex3f(-1.0f, -1.0f, 1.0f);
// 右面
glNormal3f( 1.0f, 0.0f, 0.0f);
glTexCoord2f(1.0f, 0.0f); glVertex3f( 1.0f, -1.0f, -1.0f);
glTexCoord2f(1.0f, 1.0f); glVertex3f( 1.0f, 1.0f, -1.0f);
glTexCoord2f(0.0f, 1.0f); glVertex3f( 1.0f, 1.0f, 1.0f);
glTexCoord2f(0.0f, 0.0f); glVertex3f( 1.0f, -1.0f, 1.0f);
// 左面
glNormal3f(-1.0f, 0.0f, 0.0f);
glTexCoord2f(0.0f, 0.0f); glVertex3f(-1.0f, -1.0f, -1.0f);
glTexCoord2f(1.0f, 0.0f); glVertex3f(-1.0f, -1.0f, 1.0f);
glTexCoord2f(1.0f, 1.0f); glVertex3f(-1.0f, 1.0f, 1.0f);