Wiper

WIPER


by Shimon Young





Nothing to do with windscreens or Andrex, Wiper by Shimon Young


(Shurely shome mishtake! Ed) reveals one of the 128K Speccy's


innermost secrets. The thing actually has two chunks of screen memory,


which can be swopped between at will. This means you can draw a


picture on one screen while innocently displaying the other and, when


it's finished, page in your masterpiece instantly - to the


bewilderment of onlookers. Wiper lets you do all this and (of course)


more ...





Pic 'n' Mix


Type in the short Basic loader which doubles as a demo of the


extraordinary power that is about to be unleashed. Save it onto tape


with SAVE "Wiper" LINE 1, and then hammer in the mercifully short hex


dump using the Hexloader (from Super Text Search). Save that after the


Basic part.





Now you'll need to find a couple of old saved screens from somewhere.


Having done so, reload the program which will then wait while you load


in the piccies. Finally, sit back and ogle as the two screens are


wiped between utterly smoothly and without any hint of colour clash.


Astounding. "Throw away your Quantel," as Shimes puts it.





Et Voila!


In order to make use of the routine in your own programs you'll need


the following info, all of which is alluded to in the demo.





To load a picture into the second screen area:


POKE 23388,23: LOAD "" CODE 49152.


You won't be able to see it, but it's there all right. Then to unveil


it, RANDOMIZE USR one of the following:


48946 - Wipe up


48966 - Wipe down


48983 - Boing!





You'll notice that while the second screen is paged in, all PRINTs,


PLOTs and the rest are still directed to the normal display, so you


can create your masterpiece in total secrecy and then wipe back to


reveal the results. Bear in mind, though, that every time you return


to the Basic editor the standard screen will reappear.