Pause after GL_LINE_STRIP

OpenGL OpenGL: Basic Coding
1

Hi,
I am new to OpenGL. I am working on a project where I need to read data from a input file, store coordinates in an array and then draw the image by using GL_LINE_STRIP and coordinates in the array. I also need to pause after each line is drawn so you can see the image being rendered line by line with about 0.3 second pause after each line.

I have everything finished, the problem I have is with the whole animation of lines. It hangs for a while and then draws the whole image at once, without any delay after each line.

void main(int argc, char** argv)
{
   	PromptFileName();
	CreateArray();
	ReadData();
    
    init_window(argc,argv);
    other_init(); 

    glutMainLoop();             
}

void init_window(int argc, char** argv)
{
    glutInit(&argc,argv);
	glutInitDisplayMode (GLUT_RGB); 
	glutInitWindowSize(500,400); 
	glutInitWindowPosition(0,0); 
	glutCreateWindow("2A"); 
}

void other_init()
{
	glClearColor(1.0, 1.0, 1.0, 1.0);    
    glColor3d(0.0,0.0,0.0);			    
	glMatrixMode(GL_PROJECTION);
	glLoadIdentity();
	glOrtho(-2026.0, 2026.0, -2026.0, 2026.0, -1.0, 1.0);
	glMatrixMode(GL_MODELVIEW);

    glutDisplayFunc(display); 
    glutKeyboardFunc(keyboard);
}

void display(void)
{
	glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
    glClearColor(1.0, 0.0, 1.0, 1.0);
	glClear(GL_COLOR_BUFFER_BIT);	

    for (int i=0; i<arraySize; i++){
        sleep( (clock_t) (0.3 * CLOCKS_PER_SEC ));

        glColor3f(i/10.0, 1.0, 0.0);      
//arrayPtr has the coordinates
        if (arrayPtr[i][3] == 1)    // if this row is marked as jump
        {
            if (i != 0)
                glEnd();
            glBegin(GL_LINE_STRIP);
        }
        // draw a line strip
        glVertex3f(arrayPtr[i][0], arrayPtr[i][1], 0.0);

        glFlush();                      // clear buffers
        sleep( (clock_t) (0.3 * CLOCKS_PER_SEC ));

    }

    glEnd();
    glFlush();
}

Thank you.
-Tom

2

It’s illegal to call glFlush between glBegin/glEnd.

You’ll need to draw the line segments one at a time with glBegin(GL_LINE_STRIP);glVertex3f();glVertex3f();glEnd() then sleep().

3

don’t sleep when rendering. sleep before or after. Otherwise it’s just like kicking in the air…

4

If you do not use double buffering, then you will have to use just GL_LINES and draw one line at a time, so glBegin/glVertex/glVertex/glEnd/sleep.

If you use double buffering, then you should draw entire line loop from beginning to current segment and call swapBuffers each time.

5

i guess the sleep function you are using is the one from unistd.h? in that case, the function takes only integers as arguments, and it is not possible to sleep for a fraction of a second.

you better try usleep. usleep takes an unsigned long argument, which is the number of microseconds. if you want a delay of 0.3 seconds, you need usleep(300000).

6

Maybe he’s using this sleep example from the MSDN
http://msdn.microsoft.com/library/default.asp?url=/library/en-us/vclib/html/_crt_clock.asp

7

Thank you all for your help.
Actually you are correct, I was using that sleep method. But now I am using the “Sleep(DWORD ms)” method from <windows.h>.

And my problem was trying to use glFlush() inside glBegin(…) and glEnd(). After I moved glFlush() after glEnd(), everything is working fine.

Thanks again.
-Tom

8

There’s a gem of a function in OpenGL called glGetError. If you place one of these calls after all significant blocks of GL code, you’ll have a real time saver in tracking down problems like this one. The errors themselves are pigeonholed into a handful of enums, but they’ll sure help you to confine your search. Look at gluErrorString (in glu.h) for a displayable string version of the enum returned by glGetError.

http://www.mevis.de/opengl/glGetError.html
http://www.mevis.de/opengl/gluErrorString.html