App 03

DOUBLE LO DEMO.

A tiny AppleSoft BASIC program to demonstrate the undocumented double lo-res graphics mode of the Apple //c. It was published in Nibble magazine.

The image is a screen capture of the program running in the GSSquared Apple emulator. You can download a .DSK image to run it yourself in an emulator if you'd like to see it in action.

The source code is below if you want to see how it works or make your own modifications. It was kindly updated by Stavros Karatsoriois to check for hardware compatibility before attempting to switch to double lo-res mode. He also typed in a TON of software so the complete library of Apple II software published in Nibble Magazine is available for download.

Download the .DSK image Get the emulator
App running
How it works
Check hardware
Determine if your machine is capable of showing double lo-res graphics`
→
Change Display Mode
Switch to double lo-res graphics mode
→
Make art
Draw lines on the screen to show off the new mode
Source code 
10  REM  **********************
20  REM  *   DOUBLE.LO.DEMO   *
25  REM  * BY CHRIS SCHUMANN  *
30  REM  * COPYRIGHT (C) 1986 *
40  REM  * BY MICROSPARC, INC *
50  REM  * CONCORD, MA 01742  *
60  REM  **********************
71  REM  MODIFIED FOR IIGS AND IIC PLUS BY S. KARATSORIOIS
75  GOSUB 500:GS = PEEK (788)
80  DEF FN FC(X) = INT ( RND (I) * X)
90  PRINT CHR$ (21); TEXT : HOME :D$ = CHR$ (4)
100 IF PEEK (64435) = 6 AND PEEK (64448) = 0 THEN 120
105 IF PEEK (64435) = 6 AND PEEK (64448) = 223 AND GS = 1 THEN 120
110 HOME : VTAB 12: PRINT "THIS PROGRAM ONLY WORKS ON THE //C, IIGS AND
    IIC PLUS!": END
120 IF PEEK (49248) < 128 THEN 180
125 IF GS = 1 OR PEEK (64447) = 5 THEN 180
130 HOME
140 PRINT "This program uses 80 columns. If you"
150 PRINT : PRINT "wish to use it, set the 80/40 switch to"
160 PRINT : PRINT "the UP position."
170 END
180 PRINT D$"PR#3": REM Turn on 80 Cols
190 PRINT : REM Make firmware ready
200 X = PEEK (49246): REM Double Mode
210 GR : REM Now in 80 X 40 mode
220 HOME : FOR I = 1 TO 7: PRINT TAB( I * 10 + 1);I,: NEXT
230 PRINT
240 FOR I = 1 TO 8: PRINT "0123456789"; NEXT
250 PRINT TAB( 30)"Press <RETURN> to quit."
260 XO = 0:XN = XO
270 XN = XO + 1: IF XN = 80 THEN XN = 0: REM Wrap-around
280 Z = PEEK ( - 16335): REM Click speaker
290 COLOR= 15: PLOT XN,39
300 COLOR= 0: PLOT XO,39:XO = XN
310 COLOR= FN FC(16)
320 ON ( FN R(2) > 0) GOTO 350
325 VLIN FN R(40), FN R(40) AT FN R(80)
330 GOTO 360
350 HLIN FN R(80), FN R(80) AT FN R(40)
360 IF PEEK ( - 16384) < 128 THEN 270: REM No key pressed
370 GET A$: REM Absorb key press
380 TEXT : HOME : PRINT CHR$ (21): REM 80 Cols off
390 X = PEEK (49247): REM Single Mode
400 END
500 REM DETECT IIGS ROUTINE
510 FOR AA = 0 TO 19: READ B$: POKE 768 + AA,B$: NEXT AA
520 CALL 768: RETURN
530 DATA 56,32,31,254,176,2,144,6,169,255,141,20,3,96,169,1,141,20,3,9,6