c++ - 如何允许用户在 opengl 中缩放一个对象而不缩放其他对象

Question

下面的程序正在绘制两个立方体，使用“D”/“d”键进行放大/缩小。我如何添加一个能力，其中一个立方体应该放大/缩小，而另一个不应该。

#define PI 3.1415926535898
#define Cos(th) cos(PI/180*(th))
#define Sin(th) sin(PI/180*(th))
#define DEF_D 5

/*  Globals */
double dim=5.0; /* dimension of orthogonal box */
char *windowName = "test window";
int windowWidth=500;
int windowHeight=450;

/*  Various global state */
int toggleAxes = 1;   /* toggle axes on and off */
int toggleValues = 1; /* toggle values on and off */
int toggleMode = 0; /* projection mode */
int th = 340;   /* azimuth of view angle */
int ph = 30;    /* elevation of view angle */
int fov = 55;   /* field of view for perspective */
int asp = 1;    /* aspect ratio */

/*  Cube vertices */
GLfloat vertA[3] = { 0.5, 0.5, 0.5};
GLfloat vertB[3] = {-0.5, 0.5, 0.5};
GLfloat vertC[3] = {-0.5,-0.5, 0.5};
GLfloat vertD[3] = { 0.5,-0.5, 0.5};
GLfloat vertE[3] = { 0.5, 0.5,-0.5};
GLfloat vertF[3] = {-0.5, 0.5,-0.5};
GLfloat vertG[3] = {-0.5,-0.5,-0.5};
GLfloat vertH[3] = { 0.5,-0.5,-0.5};

/*
 * project()
 * ------
 * Sets the projection
 */
void project() 
{
  glMatrixMode(GL_PROJECTION);
  glLoadIdentity();

  if (toggleMode) {
    /* perspective */
    gluPerspective(fov,asp,dim/4,4*dim);
  }
  else {
    /* orthogonal projection*/
    glOrtho(-dim*asp,+dim*asp, -dim,+dim, -dim,+dim);
  }

  glMatrixMode(GL_MODELVIEW);
  glLoadIdentity();
}

/*
 * setEye()
 * ------
 * Set the eye position
 */
void setEye()
{
  if (toggleMode) {
    double Ex = -2*dim*Sin(th)*Cos(ph);
    double Ey = +2*dim        *Sin(ph);
    double Ez = +2*dim*Cos(th)*Cos(ph);
    /* camera/eye position, aim of camera lens, up-vector */
    gluLookAt(Ex,Ey,Ez , 0,0,0 , 0,Cos(ph),0);
  }
  /*  Orthogonal - set world orientation */
  else {
    glRotatef(ph,1,0,0);
    glRotatef(th,0,1,0);
  }
}

void cube(double x,double y,double z,
      double dx,double dy,double dz,
      double th)
{
  glPushMatrix();
  /*  Transform cube */
  glTranslated(x,y,z);
  glRotated(th,0,1,0);
  glScaled(dx,dy,dz);

  /* Cube */
  glBegin(GL_QUADS);
  /* front => ABCD yellow */
  glColor3f(1.0,1.0,0.0);
  glVertex3fv(vertA);
  glVertex3fv(vertB);
  glVertex3fv(vertC);
  glVertex3fv(vertD);
  /* back => FEHG red */
  glColor3f(1.0,0.0,0.0);
  glVertex3fv(vertF);
  glVertex3fv(vertE);
  glVertex3fv(vertH);
  glVertex3fv(vertG);
  /* right => EADH green */
  glColor3f(0.0,1.0,0.0);
  glVertex3fv(vertE);
  glVertex3fv(vertA);
  glVertex3fv(vertD);
  glVertex3fv(vertH);
  /* left => BFGC blue */
  glColor3f(0.0,0.0,1.0);
  glVertex3fv(vertB);
  glVertex3fv(vertF);
  glVertex3fv(vertG);
  glVertex3fv(vertC);
  /* top => EFBA turquoise */
  glColor3f(0.0,1.0,1.0);
  glVertex3fv(vertE);
  glVertex3fv(vertF);
  glVertex3fv(vertB);
  glVertex3fv(vertA);
  /* bottom => DCGH pink */
  glColor3f(1.0,0.0,1.0);
  glVertex3fv(vertD);
  glVertex3fv(vertC);
  glVertex3fv(vertG);
  glVertex3fv(vertH);
  glEnd();

  glPopMatrix();
}

void display()
{
  glClear(GL_COLOR_BUFFER_BIT|GL_DEPTH_BUFFER_BIT);
  glEnable(GL_DEPTH_TEST);
  glLoadIdentity();

  /* setup functions */
  setEye();

  cube(2,0,1, 1,1,1, 0);
  cube(-2,0,1, 1,1,1, 0);

  glFlush();
  glutSwapBuffers();
}

void reshape(int width,int height)
{
  asp = (height>0) ? (double)width/height : 1;
  glViewport(0,0, width,height);
  project();
}

void windowKey(unsigned char key,int x,int y)
{
  /*  Exit on ESC */
  if (key == 27) exit(0);
  else if (key == 'a' || key == 'A') toggleAxes = 1-toggleAxes;
  else if (key == 'v' || key == 'V') toggleValues = 1-toggleValues;
  else if (key == 'm' || key == 'M') toggleMode = 1-toggleMode;
  /*  Change field of view angle */
  else if (key == '-' && key>1) fov--;
  else if (key == '+' && key<179) fov++;
  /*  Change dimensions */
  else if (key == 'D') dim += 0.1;
  else if (key == 'd' && dim>1) dim -= 0.1;

  project();
  glutPostRedisplay();
}

int main(int argc,char* argv[])
{
  glutInit(&argc,argv);
  glutInitDisplayMode(GLUT_RGB | GLUT_DOUBLE | GLUT_DEPTH);
  glutInitWindowSize(windowWidth,windowHeight);
  glutCreateWindow(windowName);
  glutDisplayFunc(display);
  glutReshapeFunc(reshape);
  glutKeyboardFunc(windowKey);
  glutMainLoop();
  return 0;
}

我只想放大/缩小一个立方体，而不是另一个立方体。该怎么做？

Answer 1

在调用 cube 函数之前在 push pop 矩阵中进行转换。就像您只需要为立方体 1 做一样。

  glPushMatrix(); // Set current matrix on the stack
   //Scale Cube Transformations based upon your D/d value.
  glScaled(dim,dim,0)--> change how much you want, also apply other     transformations on where you want to scale.
   //Draw
  Cube(2,0,1, 1,1,1, 0);
  glPopMatrix(); // Pop the old matrix without the transformations.

  Then draw the other cube.
  cube(-2,0,1, 1,1,1, 0);