4.8 3D Overlay Mode
While the <3> command (see "3D" Images (p. 106)) creates its image on a
blank screen, the <#> (or <shift-3> on some keyboards) command draws a
second image over an existing displayed image. This image can be any
restored image from a <R> command or the result of a just executed <3>
command. So you can do a landscape, then press <#> and choose spherical
projection to re-plot that image or another as a moon in the sky above
the landscape. <#> can be repeated as many times as you like.
It's worth noting that not all that many years ago, one of us watched
Benoit Mandelbrot and fractal-graphics wizard Dick Voss creating just
such a moon-over-landscape image at IBM's research center in Yorktown
Heights, NY. The system was a large and impressive mainframe with
floating-point facilities bigger than the average minicomputer, running
LBLGRAPH -- what Mandelbrot calls "an independent-minded and often very
ill-mannered heap of graphics programs that originated in work by Alex
Hurwitz and Jack Wright of IBM Los Angeles."
We'd like to salute LBLGRAPH, its successors, and their creators,
because it was their graphic output (like "Planetrise over Labelgraph
Hill," plate C9 in Mandelbrot's "Fractal Geometry of Nature") that
helped turn fractal geometry from a mathematical curiosity into a
phenomenon. We'd also like to point out that it wasn't as fast, flexible
or pretty as Fractint on a 386/16 PC with S-VGA graphics. Now, a lot of
the difference has to do with the incredible progress of micro-processor
power since then, so a lot of the credit should go to Intel rather than
to our highly tuned code. OK, twist our arms -- it IS awfully good code.