Chapter 8

Not too shabby for rank amateurs.

Here’s what happens:

Line 10 clears the screen.

Line 20 selects the “low memory” HIRES page. This part of memory is used for high-resolution graphics, while text is stored on a different ‘page’ of memory.

48K disk users have two different chunks of memory that can be used for HIRES graphics. If we wanted, we could store 2 different pictures at the same time. Refer to the Apple Programming Reference Manual for more information.

Line 30 selects a color.

Lines 40 and 70 set up a loop for plotting a figure.

Line 50 calculates the radius as a function of the angle. We are using polar coordinates in case you hadn’t guessed. If you don’t really care, it doesn’t really matter - the picture is still pretty.

Line 60 converts from polar to rectangular coordinates and plots a single point. Whew! It’s a good thing computers don’t require a good math background.

Why All This Math?

Using Math equations to create graphics is easier than by doing it the hard way, point-by-point. They do, however, restrict us to graphs or plots of natural phenomena, and who among us will claim credit for creativity in that area‘?

Type:

TEXT

to return back to the TEXT page. Even though we can’t see it, the picture remains stored in the HI-RES page of memory.

We can play with line 50 to get different figures. Try:

50 R=3 * A

and

72