c++ - 仅显示 1 个 opengl 3d 立方体

Question

我的 opengl 程序有问题。我只能显示一个立方体。我试图显示两个立方体，但似乎无法弄清楚为什么只显示一个立方体。有人可以告诉我为什么以及我需要做些什么来纠正它吗？我必须使用的立方体函数是:

void myCube(double length)
{ 

double half = length/2;
// face 1
glBegin(GL_POLYGON);
   glVertex3d(half, -half, half); 
   glVertex3d(half, half, half); 
   glVertex3d(-half, half, half); 
   glVertex3d(-half, -half, half); 
glEnd();
// face 2
glPushMatrix();
glBegin(GL_POLYGON);
   glVertex3d(half, -half, -half); 
   glVertex3d(half, half, -half); 
   glVertex3d(-half, half, -half); 
   glVertex3d(-half, -half, -half); 
glEnd();
// face 3
glBegin(GL_POLYGON);
   glVertex3d(half, half, half); 
   glVertex3d(half, -half, half); 
   glVertex3d(half, -half, -half); 
   glVertex3d(half, half, -half); 
glEnd();
// face 4
glBegin(GL_POLYGON);
   glVertex3d(-half, -half, half); 
   glVertex3d(-half, half, half); 
   glVertex3d(-half, half, -half); 
   glVertex3d(-half, -half, -half); 
glEnd();
// face 5
glBegin(GL_POLYGON);
   glVertex3d(half, half, half); 
   glVertex3d(half, half, -half); 
   glVertex3d(-half, half, -half); 
   glVertex3d(-half, half, half); 
glEnd();
// face 6
glBegin(GL_POLYGON);
   glVertex3d(half, -half, half); 
   glVertex3d(half, -half, -half); 
   glVertex3d(-half, -half, -half); 
   glVertex3d(-half, -half, half); 
glEnd();

}

这是我的显示功能:

void myDisplay(void)
{
//cubeCount = (rand() % 15) + 7;
//int r = rand()%18;
//r = r - 9;
//double rd = (double)r / 2.0;
//glMatrixMode(GL_PROJECTION); // set the view volume shape
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
{
glMatrixMode(GL_MODELVIEW);
glLoadIdentity();
//glTranslatef(1.0f, 4.0f, 2.0f);
//double factor = 05;
gluPerspective(60, screenWidth/screenHeight, 0.1, 100);
gluLookAt(3.0, 3.0, -3.0, 3.0, 3.0, 0.0, 0.0, 1.0, 0.0);

//for (int i = 0; i < 5; i++)
//{
    glPushMatrix();
    glTranslatef(4.9f, 1.2f, 1.0f);
    glRotated(45.0, 0.0, 1.0, 0.0);
    glColor3d(1, 1, 1); // draw white cube
    glEnable(GL_POLYGON_OFFSET_FILL);
    glPolygonOffset(1.0, 1.0);  
    myCube(0.5);
    glDisable(GL_POLYGON_OFFSET_FILL);
    glColor3d(0, 0, 0); // draw black lines
    glPolygonMode(GL_FRONT_AND_BACK, GL_LINE);
    myCube(0.5);
    glPopMatrix();
    //glFlush();

    glPushMatrix();
    glTranslatef(2.0f, 4.0f, 2.0f);
    glScalef(1.0, 2.0, 1.0);
    //glRotated(45.0, 0.0, 1.0, 0.0);
    glColor3d(1, 1, 1); // draw white cube
    glEnable(GL_POLYGON_OFFSET_FILL);
    glPolygonOffset(1.0, 1.0);  
    myCube(0.5);
    glDisable(GL_POLYGON_OFFSET_FILL);
    glColor3d(0, 0, 0); // draw black lines
    glPolygonMode(GL_FRONT_AND_BACK, GL_LINE);
    myCube(0.5);
    glPopMatrix();
//}
}
//glutSwapBuffers();
glFlush();
}

我在显示屏的左下角看到了一个立方体，但另一个立方体没有显示在任何地方。如果需要，我会上传更多代码。

Answer 1

现在你正在用重复的不匹配的 glPushMatrix()es 遍历你的模型 View 矩阵堆栈。

从 myCube() 中调用 glPushMatrix():

...
   glVertex3d(-half, -half, half); 
glEnd();
// face 2
glPushMatrix();
^^^^^^^^^^^^^^ What's this guy doing here?  
               Why doesn't it have a matching glPopMatrix()?
glBegin(GL_POLYGON);
   glVertex3d(half, -half, -half); 
.....

完整代码:

#include <GL/glut.h>

void myCube(double length)
{ 
    double half = length/2;
    // face 1
    glBegin(GL_POLYGON);
       glVertex3d(half, -half, half); 
       glVertex3d(half, half, half); 
       glVertex3d(-half, half, half); 
       glVertex3d(-half, -half, half); 
    glEnd();
    // face 2
    glBegin(GL_POLYGON);
       glVertex3d(half, -half, -half); 
       glVertex3d(half, half, -half); 
       glVertex3d(-half, half, -half); 
       glVertex3d(-half, -half, -half); 
    glEnd();
    // face 3
    glBegin(GL_POLYGON);
       glVertex3d(half, half, half); 
       glVertex3d(half, -half, half); 
       glVertex3d(half, -half, -half); 
       glVertex3d(half, half, -half); 
    glEnd();
    // face 4
    glBegin(GL_POLYGON);
       glVertex3d(-half, -half, half); 
       glVertex3d(-half, half, half); 
       glVertex3d(-half, half, -half); 
       glVertex3d(-half, -half, -half); 
    glEnd();
    // face 5
    glBegin(GL_POLYGON);
       glVertex3d(half, half, half); 
       glVertex3d(half, half, -half); 
       glVertex3d(-half, half, -half); 
       glVertex3d(-half, half, half); 
    glEnd();
    // face 6
    glBegin(GL_POLYGON);
       glVertex3d(half, -half, half); 
       glVertex3d(half, -half, -half); 
       glVertex3d(-half, -half, -half); 
       glVertex3d(-half, -half, half); 
    glEnd();
}

void display()
{
    glClearColor( 0.3, 0.3, 0.3, 1 );
    glClear( GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT );

    glMatrixMode( GL_PROJECTION );
    glLoadIdentity();
    double w = glutGet( GLUT_WINDOW_WIDTH );
    double h = glutGet( GLUT_WINDOW_HEIGHT );
    gluPerspective( 60, w / h, 0.1, 100 );

    glMatrixMode( GL_MODELVIEW );
    glLoadIdentity();
    gluLookAt(3.0, 3.0, -3.0, 3.0, 3.0, 0.0, 0.0, 1.0, 0.0);

    glPushMatrix();
    {
        glTranslatef(4.9f, 1.2f, 1.0f);
        glRotated(45.0, 0.0, 1.0, 0.0);

        glColor3d(1, 1, 1);
        glPolygonMode( GL_FRONT_AND_BACK, GL_FILL );
        glEnable( GL_POLYGON_OFFSET_FILL );
        glPolygonOffset( 1.0, 1.0 );  
        myCube( 0.5 );
        glDisable( GL_POLYGON_OFFSET_FILL );

        glColor3d(0, 0, 0);
        glPolygonMode( GL_FRONT_AND_BACK, GL_LINE );
        myCube( 0.5 );
    }
    glPopMatrix();

    glPushMatrix();
    {
        glTranslatef(2.0f, 4.0f, 2.0f);
        glScalef(1.0, 2.0, 1.0);

        glColor3d(1, 1, 1);
        glPolygonMode( GL_FRONT_AND_BACK, GL_FILL );
        glEnable( GL_POLYGON_OFFSET_FILL );
        glPolygonOffset( 1.0, 1.0 );  
        myCube( 0.5 );
        glDisable( GL_POLYGON_OFFSET_FILL );

        glColor3d(0, 0, 0);
        glPolygonMode( GL_FRONT_AND_BACK, GL_LINE );
        myCube( 0.5 );
    }
    glPopMatrix();

    glutSwapBuffers();
}

int main( int argc, char **argv )
{
    glutInit( &argc, argv );
    glutInitDisplayMode( GLUT_RGBA | GLUT_DEPTH | GLUT_DOUBLE );
    glutInitWindowSize( 640, 480 );
    glutCreateWindow( "GLUT" );
    glutDisplayFunc( display );
    glutMainLoop();
    return 0;
}