How to draw real time 2D graph using OpenGL in MVS

Question

I am writing a code that receives heart sound from a hardware device using comports and plots the signal received. I am using OpenGl to plot the signal received. I am able to plot when I receive the complete data. But I want the graph to update with the updating of data received Here is my code:

    int num_samples = 100000;


long samples[100000];
DWORD        bytes_read    = 0;    // Number of bytes read from port


/* Function plotting func */
void draw( float x1, float x2, float y1, float y2, int N)
{
    float x, dx = 1.0/N; 
glPushMatrix(); /* GL_MODELVIEW is default */

glScalef(1.0 / (x2 - x1), 1.0 / (y2 - y1), 1.0);
glTranslatef(-x1, -y1, 0.0);
glColor3f(1.0, 1.0, 1.0);

glBegin(GL_LINE_STRIP); 
int k =0;
for(x = 0; x < num_samples; x += dx)
{
    glVertex2f(x, samples[k]);
    k=k+1;
}

glEnd();

glPopMatrix();

glFlush();
};

/* Redrawing func */
void redraw(void)
{
    glClearColor(0, 0, 0, 0);
    glClear(GL_COLOR_BUFFER_BIT);
    glMatrixMode(GL_MODELVIEW);
    glLoadIdentity();
    //long buf = getBuffer(samples);
    draw(0, num_samples,-693554432, 693554432, 1);
    //  draw(func, 0, 1000,0, 5000, 1);

    glutSwapBuffers();
    //glFlush();
};

/* Idle proc. Redisplays, if called. */
void idle(void)
{
    glutPostRedisplay();
};

/* Key press processing */
void key(unsigned char c, int x, int y)
{
    if(c == 27) exit(0);
};

/* Window reashape */
void reshape(int w, int h)
{
    glViewport(0, 0, w, h);
    glMatrixMode(GL_PROJECTION);
    glLoadIdentity();
    glOrtho(0, 1, 0, 1, -1, 1);
    glMatrixMode(GL_MODELVIEW);
};
/*
long putBuffer(long[] buffer)
{
    return buffer;
}*/

 //Main function 

int j =0;
unsigned long size = 400000;

int main(int argc, char* argv[])
{
    unsigned char INBUFFER[400000];

    char OUTBUFFER[20];
    DWORD        bytes_read    = 0;    // Number of bytes read from port
    DWORD        bytes_written = 0;    // Number of bytes written to the port
    HANDLE       comport      = NULL;  // Handle COM port
 int   bStatus;
    DCB          comSettings;          // Contains various port settings
    COMMTIMEOUTS CommTimeouts;
    strcpy(&OUTBUFFER[0], "The quick brown fox jumped over the lazy dog. \n\r\0");
    // Open COM port
    if ((comport = 
         CreateFile("\\\\.\\COM44",                // open com5:
                    GENERIC_READ | GENERIC_WRITE, // for reading and writing
                    0,                            // exclusive access
                    NULL,                         // no security attributes
                    OPEN_EXISTING,              
                    FILE_ATTRIBUTE_NORMAL,
                    NULL)) == INVALID_HANDLE_VALUE)
    {
       // cout<<"Port can't be opened"<<endl;
    }
    // Set timeouts in milliseconds
//  cout<<"Port opened"<<endl;
    //DCB dcb;
    CommTimeouts.ReadIntervalTimeout         = 0; 
    CommTimeouts.ReadTotalTimeoutMultiplier  = 0; 
    CommTimeouts.ReadTotalTimeoutConstant    = 100;
    CommTimeouts.WriteTotalTimeoutMultiplier = 0;
    CommTimeouts.WriteTotalTimeoutConstant   = 100;
    bStatus = SetCommTimeouts(comport,&CommTimeouts);
    if (bStatus != 0)
    {
        // error processing code goes here
    }
    // Set Port parameters.
    // Make a call to GetCommState() first in order to fill
    // the comSettings structure with all the necessary values.
    // Then change the ones you want and call SetCommState().
    GetCommState(comport, &comSettings);
   // memset(&dcb,0,sizeof(dcb));

    comSettings.fBinary = 1;
    comSettings.fDtrControl = DTR_CONTROL_ENABLE;
    comSettings.fRtsControl = RTS_CONTROL_ENABLE;
    comSettings.fOutxCtsFlow = 1;
    comSettings.fRtsControl = DTR_CONTROL_HANDSHAKE;


    comSettings.BaudRate = 921600;
    comSettings.StopBits = ONESTOPBIT;
    comSettings.ByteSize = 8;
    comSettings.Parity   = NOPARITY;
    comSettings.fParity  = FALSE;

    bStatus = SetCommState(comport, &comSettings);
    ofstream outdata;
     outdata.open("hsm.txt"); // opens the file
   if( !outdata ) { // file couldn't be opened
      cerr << "Error: file could not be opened" << endl;
      exit(1);
   }
    if (bStatus == 0)
    {
        // error processing code goes here
    }
    int flag = 1;
    int fl =1;
    glutInit(&argc, argv);
    glutInitWindowSize(500,500);
    glutInitWindowPosition(500,200);
    glutInitDisplayMode(GLUT_RGB | GLUT_DOUBLE);


    //glutMainLoop();

  while(flag<120)
   {

        bStatus = ReadFile(comport,   // Handle
                &INBUFFER,            // Incoming data
                size,                  // Number of bytes to read
                &bytes_read,          // Number of bytes read
                NULL);
        if (bStatus != 0)
        {
            //cout<<"Error receiving"<<endl;
        }
//  long samples[100000];

 for (int i=0; i<bytes_read; i++)
 {
    if((unsigned char)INBUFFER[i]==0x99&&(unsigned char)INBUFFER[i+4]==0x99)

    {
    samples[j] = 0x00|(unsigned char)INBUFFER[i+1]<<8|(unsigned char)INBUFFER[i+2]<<16|(unsigned char)INBUFFER[i+3]<<24;
    if(samples[j]!=0)
         {
          outdata << samples[j] <<"\n";
          j++;
         }      
    }


 } 

    flag++;
    glutCreateWindow("Graph plotter");
    glutDisplayFunc(redraw);
    glutReshapeFunc(reshape);
    glutIdleFunc(idle);
    glutMainLoop();

  }
  CloseHandle(comport);
outdata.close();


 return 0;
}

Basically when the samples buffer gets updated, the graph should also update. But the graph is plotted in first iteration and then nothing happens. Can anyone tell me how to fix it?

Answer 1

When you call glutMainLoop, it will draw the screen, handle window events, and call the idle function repeatedly. Since all your idle function does now is to ask for the screen to be redrawn, it will not be reading additional samples from your input serial port.

You should try reading from the serial port and populating additional samples when your idle function is called.