GLUT timer loop stopping prematurely - c

Question

I've encountered a strange issue where glutTimerFunc seems to randomly stop working when I call it with a zero delay.
Here is my code:
#include <Windows.h>
#include <GL/gl.h>
#include <GL/glut.h>
int x = 0;
void init(void)
{
glClearColor(0.0, 0.0, 0.0, 1.0);
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
glOrtho(0.0, 1.0, 0.125, 0.875, -1.0, 1.0);
}
void display(void)
{
glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT);
glBegin(GL_POLYGON);
glColor3f(1.0, x ? 1.0 : 0.0, 0.0);
glVertex3f(0.25, 0.25, 0.0);
glVertex3f(0.75, 0.25, 0.0);
glVertex3f(0.75, 0.75, 0.0);
glVertex3f(0.25, 0.75, 0.0);
glEnd();
glFlush();
glutSwapBuffers();
}
void timer(int value)
{
x = !x;
glutPostRedisplay();
glutTimerFunc(0, timer, 0); // The line in question
}
int main(int argc, char** argv)
{
glutInit(&argc, argv);
glutInitDisplayMode(GLUT_DOUBLE | GLUT_RGB);
glutInitWindowSize(800, 600);
glutInitWindowPosition(200, 200);
glutCreateWindow("hello");
init();
glutDisplayFunc(display);
glutTimerFunc(0, timer, 0);
glutMainLoop();
return 0;
}
I expected this to show a flickering square, that is changing color as fast as the GPU can keep up.
That is what it actually does initially, but the timer loop seems to randomly stop, and the square stops changing color. Sometimes it doesn't flicker perceptibly at all, and sometimes it flickers for several seconds before stopping.
It doesn't stop if I set the delay to 1ms (glutTimerFunc(1, timer, 0);).
Why does the timer loop stop unexpectedly?
I don't really care about how to fix it, just why it happens.

Answer 1

Your GPU is changing the value faster than your monitor can draw it.
If you had a monitor with an extremely high refresh rate, you could probably see it, but unfortunately we're limited to 60Hz/120Hz/240Hz for now.
When you remove the 1ms forced delay, you are causing the system to become a non-deterministic system (based on the speed of other programs, rather than just yours), and that's why you're getting the random behavior.