simple graphic pipeline in OpenGL - opengl

Question

I am reading Schaum's outlines COMPUTER GRAPHICS. Book says that a simple graphic pipeline is something like this: geometric representation --> transformation --> scan conversion
(though the author has decided to teach scan conversion chapter before transformation chapter). I wish to learn this simple pipeline through an example in openGL. suppose I wish to create a line with end coordinates (150,400) and (700,100) in window of size (750,500). Below code works very well. All I am asking to experts is to explain the 'steps in sequence' when is transformation happening and when scan conversion. I know it may sound stupid but I really need to get this straight. I am just an adult beginner learning graphics at my own as a hobby.
My guess is that scan conversion is not happening here in program. it is done by openGL automatically between glBegin and glEnd calls. Am I right?
#include <GL/glut.h>
void init(void)
{
glClearColor (0.5, 0.2, 0.3, 0.0);
glClear (GL_COLOR_BUFFER_BIT);
glColor4f(0.5,0.7,0.3,0.0);
glLineWidth(3);
}
void display(void)
{
glBegin(GL_LINES);
glVertex2i(50, 400);
glVertex2i(700, 100);
glEnd();
glutSwapBuffers();
}
void reshape(int w, int h)
{
glViewport(0, 0, (GLsizei) w, (GLsizei) h);
glMatrixMode(GL_PROJECTION);
glLoadIdentity();
gluOrtho2D(0.0, (GLdouble)w, 0.0, (GLdouble)h);
}
int main (int argc, char *argv[])
{
glutInit(&argc, argv);
glutInitDisplayMode (GLUT_RGBA | GLUT_DEPTH);
glutInitWindowPosition(100,150);
glutInitWindowSize(750,500); // aspect ratio of 3/2
glutCreateWindow (argv[0]);
init();
glutDisplayFunc(display);
glutReshapeFunc(reshape);
glutMainLoop(); // this is when the frame buffer is displayed on the screen
return (0);
}

Answer 1

All stages done within OpenGL implementation (mostly in hardware). You specify states and data, then GL will - if speaking in terms of old GL 1.0 - assemble data into vertices, pass every vertex through transformation stage, rasterize resulting primitives into fragments, perform per-fragment tests (that may discard some fragments), and update resulting pixels on render target.
There is no point in user code that may be on 'one stage' in pipeline - it doesn't have callbacks, and usually as many as possible stages working at the same time.