/* Draw circles of radius 9, 8 and 7 with the colours shown around (0,0)

Draw the x and y axis

Draw the diagonal line

Draw the 12 by 6 quad around (0,0)

When the left mouse button is pressed the diagonal line moves as shown.

When the right button is pressed the diagonal line is reset to its

original position

The right button also toggles the direction from + to - x

Pressing Esc exits the program

*/-/* Draw circles of radius 9, 8 and 7 with the colours shown around (0,0)

　 Draw the x and y axis

　 Draw the diagonal line

　 Draw the 12 by 6 quad around (0,0)

　 When the left mouse button is pressed the diagonal line moves as shown.

　 When the right button is pressed the diagonal line is reset to its

　 original position

　 The right button also toggles the direction from+ to- x

　 Pressing Esc exits the program

*/