c - 接收UDP数据时移动OpenGL机械臂？

Question

我有这段代码，主要思想是绘制一个机器人 ARM ，并在使用 UDP 从 9090 端口接收到数据时移动它。

我想弄清楚为什么在显示机械臂后，控制台上没有显示任何消息。

此外，我想知道如何修改 if(number%2 ==0) 之后的代码以移动 ARM 。

#include <GL/glut.h>
#include <math.h>
#define BASE_HEIGHT 4.0/2
#define BASE_RADIUS 1.0/2
#define HEAD_HEIGHT 1.25/2
#define HEAD_RADIUS 0.75/2
#define NECK_HEIGHT 0.5/2
#define EYE_LEVEL 0.75/2
#define NOSE_LENGTH 0.5/2
#define LOWER_ARM_HEIGHT 2.0/2
#define LOWER_ARM_WIDTH 0.5/2
#define UPPER_ARM_HEIGHT 1.25/2
#define UPPER_ARM_WIDTH 0.5/2
#define ARM_TRANSLATION 0.22/2
#define alpha 0.0
#define pi 3.14159265
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <netdb.h>
#include <sys/socket.h>
#include <arpa/inet.h>

#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <netdb.h>
#include <sys/socket.h>
#include <arpa/inet.h>
#define BUFSIZE 2048
//***********************
    struct sockaddr_in myaddr;  /* our address */
    struct sockaddr_in remaddr; /* remote address */
    socklen_t addrlen = sizeof(remaddr);        /* length of addresses */
    int recvlen;            /* # bytes received */
    int fd;             /* our socket */
    unsigned char buf[BUFSIZE]; /* receive buffer */


#define SERVICE_PORT    9090 


int a2i(unsigned char *s)
{
 int sign=1;
 if(*s == '-')
        sign = -1;
 s++;
 int num=0;
 while(*s)
  {
    num=((*s)-'0')+num*10;
    s++;   
  }
 return num*sign;
}
// The robot arm is specified by (1) the angle that the upper arm makes
// relative to the x-axis, called shoulderAngle, and (2) the angle that the
// lower arm makes relative to the upper arm, called elbowAngle.  These angles
// are adjusted in 5 degree increments by a keyboard callback.
static int shoulderAngle = 0, elbowAngle = 0;

// Handles the keyboard event: the left and right arrows bend the elbow, the
// up and down keys bend the shoulder.
void special(int key, int, int) {
  switch (key) {
    case GLUT_KEY_LEFT: (elbowAngle += 5) %= 360; break;
    case GLUT_KEY_RIGHT: (elbowAngle -= 5) %= 360; break;
    case GLUT_KEY_UP: (shoulderAngle += 5) %= 360; break;
    case GLUT_KEY_DOWN: (shoulderAngle -= 5) %= 360; break;
    default: return;
  }
  glutPostRedisplay();
}

// wireBox(w, h, d) makes a wireframe box with width w, height h and
// depth d centered at the origin.  It uses the GLUT wire cube function.
// The calls to glPushMatrix and glPopMatrix are essential here; they enable
// this function to be called from just about anywhere and guarantee that
// the glScalef call does not pollute code that follows a call to myWireBox.
void wireBox(GLdouble width, GLdouble height, GLdouble depth) {
  glPushMatrix();
  glScalef(width, height, depth);
  glutWireCube(1.0);
  glPopMatrix();
}

// Displays the arm in its current position and orientation.  The whole
// function is bracketed by glPushMatrix and glPopMatrix calls because every
// time we call it we are in an "environment" in which a gluLookAt is in
// effect.  (Note that in particular, replacing glPushMatrix with
// glLoadIdentity makes you lose the camera setting from gluLookAt).
void display() {

  glClear(GL_COLOR_BUFFER_BIT);
  glMatrixMode(GL_MODELVIEW);
  glPushMatrix();

  // Draw the upper arm, rotated shoulder degrees about the z-axis.  Note that
  // the thing about glutWireBox is that normally its origin is in the middle
  // of the box, but we want the "origin" of our box to be at the left end of
  // the box, so it needs to first be shifted 1 unit in the x direction, then
  // rotated.
  glRotatef((GLfloat)shoulderAngle, 0.0, 0.0, 1.0);
  glTranslatef(1.0, 0.0, 0.0);
  wireBox(2.0, 0.4, 1.0);

  // Now we are ready to draw the lower arm.  Since the lower arm is attached
  // to the upper arm we put the code here so that all rotations we do are
  // relative to the rotation that we already made above to orient the upper
  // arm.  So, we want to rotate elbow degrees about the z-axis.  But, like
  // before, the anchor point for the rotation is at the end of the box, so
  // we translate <1,0,0> before rotating.  But after rotating we have to
  // position the lower arm at the end of the upper arm, so we have to
  // translate it <1,0,0> again.
  glTranslatef(1.0, 0.0, 0.0);
  glRotatef((GLfloat)elbowAngle, 0.0, 0.0, 1.0);
  glTranslatef(1.0, 0.0, 0.0);
  wireBox(2.0, 0.4, 1.0);

  glPopMatrix();
  glFlush();
}

// Handles the reshape event by setting the viewport so that it takes up the
// whole visible region, then sets the projection matrix to something reason-
// able that maintains proper aspect ratio.
void reshape(GLint w, GLint h) {
  glViewport(0, 0, w, h);
  glMatrixMode(GL_PROJECTION);
  glLoadIdentity();
  gluPerspective(65.0, GLfloat(w)/GLfloat(h), 1.0, 20.0);
}

// Perfroms application specific initialization: turn off smooth shading,
// sets the viewing transformation once and for all.  In this application we
// won't be moving the camera at all, so it makes sense to do this.
void init() {
  glShadeModel(GL_FLAT);
  glMatrixMode(GL_MODELVIEW);
  glLoadIdentity();
  gluLookAt(1,2,8, 0,0,0, 0,1,0);
}

// Initializes GLUT, the display mode, and main window; registers callbacks;
// does application initialization; enters the main event loop.
int main(int argc, char** argv) {



    /* create a UDP socket */

    if ((fd = socket(AF_INET, SOCK_DGRAM, 0)) < 0) {
        perror("cannot create socket\n");
        return 0;
    }

    /* bind the socket to any valid IP address and a specific port */

    memset((char *)&myaddr, 0, sizeof(myaddr));
    myaddr.sin_family = AF_INET;
    myaddr.sin_addr.s_addr = htonl(INADDR_ANY);
    myaddr.sin_port = htons(SERVICE_PORT);

    if (bind(fd, (struct sockaddr *)&myaddr, sizeof(myaddr)) < 0) {
        perror("bind failed");
        return 0;
    }


  glutInit(&argc, argv);
  glutInitDisplayMode(GLUT_SINGLE | GLUT_RGB);
  glutInitWindowPosition(80, 80);
  glutInitWindowSize(800, 600);
  glutCreateWindow("Robot Arm");
  glutDisplayFunc(display);
  glutReshapeFunc(reshape);
  glutSpecialFunc(special);
  init();
  glutMainLoop();

    /* now loop, receiving data and printing what we received */
    for (;;) {
        printf("waiting on port %d\n", SERVICE_PORT);
        recvlen = recvfrom(fd, buf, BUFSIZE, 0, (struct sockaddr *)&remaddr, &addrlen);
        printf("received %d bytes\n", recvlen);



        if (recvlen > 0) {
            buf[recvlen] = 0;
            printf("received message: \"%s\"\n", buf);
            int number = a2i( buf );
            if(number%2 ==0) {
            printf("pair message: \"%s\"\n", buf);





                    }
        }
    }
    /* never exits */

//*******************


}

Answer 1

glutMainLoop()永不返回:

glutMainLoop enters the GLUT event processing loop. This routine should be called at most once in a GLUT program. Once called, this routine will never return. It will call as necessary any callbacks that have been registered.

您有多种选择:

• 切换到非阻塞套接字并在 glutIdleFunc() 回调中为您的网络连接提供服务。
• 使用FreeGLUT的 glutMainLoopEvent() 和 friend 们来夺回对事件循环的一些控制权。请注意阻止等待网络流量的时间。
• 继续使用阻塞套接字并启动线程来服务网络连接；如何将状态更新从线程传递到主程序取决于您。