opengl code compilation issue - opengl

Question

After drawing a shape am not been able to draw any more shapes in my display function. But it is being drawn perfectly in other methods but not in my glutidlefunction(myDispalay). Stuck here for about two days. can anyone help me out from here ?
Here is the code :
include < stdio.h>
include< math.h>
include < GL/glut.h>
define PI 3.1416
float x,y,r,y2,r2;
void drawCircle(float x, float y, float radius)
{
int i;
int triangleAmount = 1000; //# of triangles used to draw circle
float twicePi = 2.0f * PI;
glBegin(GL_TRIANGLE_FAN);
for(i = 0; i <= triangleAmount;i++)
{
glVertex2f( x + (radius * cos(i * twicePi / triangleAmount)),
y + (radius * sin(i * twicePi / triangleAmount)));
}
glEnd();
}
void drawthrower()
{
glClear(GL_COLOR_BUFFER_BIT);
glColor3f(0.0,1.0,0.0);
drawCircle(x,y,r);
glBegin(GL_LINES);
glVertex2i(x-12,y-28);
glVertex2i(x-12,y-70);
glVertex2i(x+12,y-28);
glVertex2i(x+12,y-70);
glEnd();
drawCircle(x,y2,r2);
glutSwapBuffers();
}
void myDisplay()
{
while ((x+r)<=1024)
{
x+=8;
drawthrower();
}
while ((x-r)>=0)
{
x-=8;
drawthrower();
}
}
void myInit()
{
glClearColor(1,1,1,1);
x=50,y=693,r=30,x=50,y2=623,r2=12;
}
void reshape(int w, int h)
{
glViewport(0, 0, (GLsizei) w, (GLsizei) h);
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
glOrtho(0.0, 1024.0, 0.0, 768.0, 0.0, 1.0);
glMatrixMode(GL_MODELVIEW);
}
int main(int argc, char** argv)
{
glutInit(&argc, argv);
glutInitDisplayMode(GLUT_DOUBLE | GLUT_RGB);
glutInitWindowSize(1024,768);
glutInitWindowPosition(0, 0);
glutCreateWindow("Graphics_Project");
myInit();
glutReshapeFunc(reshape);
glutIdleFunc(myDisplay);
glutMainLoop();
return 0;
}

Answer 1

When using GLUT drawing code should be isolated to the display callback function. You're currently have the display function registered as idle function. To make the program call the display function continuously call glutPostRedisplay from the idle function (or register glutPostRedisplay as the idle function). The reason why you should limit drawing code to the display callback is, that depending on the OS when the redraw event is sent certain special state may be set.
Also, while not technically wrong, but a stylistic issue is, that the glutSwapBuffers should be moved into the display function, so that when maintaining the program one does not go hunting for details like in which subroutine the buffer swap is carried out.