Reshaping the Window in OpenGL

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Now as the window is reshaped, you may notice in the other programs,
that it might act a little weird, in this we add the 'reshape'
function. This sets up our View Port and our Perspective mode with
its parameters.
Our glViewport, starts at 0,0 the top left hand corner, and goes
until it reaches the height and width of our window. So from the top
left to the bottom right.
By setting our Matrix Mode to GL_PROJECTION we can play with the 'camera'.
We are setting up our 'camera' to a Perspective mode, this means that
things in the distance appear smaller than those closer to the 'camera'.
Now I will explain the line:
gluPerspective (60, (GLfloat)w / (GLfloat)h, 1.0, 100.0);
Our first value here is the angle of sight, so if you could stick your
arms out infront of you in a 60 degree angle and erase everything on the
outside, what is on the inside is what you would see. The next value determines
the aspect ratio of the field of sight in the x direction, where x is the
ratio of x(width) / y(height), then comes the value of 1.0, this is the near factor,
and this is the closest something can get to the 'camera' before dissappearing. Last
is the value 100, this is the far value and is how far the camera can see, so
anything further than 100 would not be drawn.

After this we switch back to our ModelView MatrixMode so we can edit our objects.

#include <GL/gl.h>
#include <GL/glut.h>

void cube (void) {
glutWireCube(2);
}

void display (void) {
glClearColor (0.0,0.0,0.0,1.0);
glClear (GL_COLOR_BUFFER_BIT);
glLoadIdentity();
gluLookAt (0.0, 0.0, 5.0, 0.0, 0.0, 0.0, 0.0, 1.0, 0.0);
cube();
glFlush();
}

void reshape (int w, int h) {
glViewport (0, 0, (GLsizei)w, (GLsizei)h);
glMatrixMode (GL_PROJECTION); //set it so we can play with the 'camera'
glLoadIdentity (); //replace the current matrix with the Identity Matrix
gluPerspective (60, (GLfloat)w / (GLfloat)h, 1.0, 100.0); //set the angle of view, the ratio of sight, the near and far factors
glMatrixMode (GL_MODELVIEW); //switch back the the model editing mode.
}

int main (int argc, char **argv) {
glutInit (&argc, argv);
glutInitDisplayMode (GLUT_SINGLE);
glutInitWindowSize (500, 500); //set the size of the window
glutInitWindowPosition (100, 100); //set the position of the window
glutCreateWindow ("A basic OpenGL Window");
glutDisplayFunc (display);
glutReshapeFunc (reshape);
glutMainLoop ();
return 0;
}

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