Help with Custom Display List

[91SNESplayer]

Hello! I’m trying to create a custom display list on Atari Basic with 20 lines of Graphics 3 on top and 2 lines of Graphics 2 on the bottom, alas with no success. Can someone point me in the right direction on how I could do this?

[vitoco]

What have you done so far?

[zbyti]

PEEK your actual DL (BASIC 0) address and start poking existing DL from that address.

 

 

 

Edited December 6, 2020 by zbyti
screenshot

[fenrock]

I use this site to help, it exports values (in many formats) and validates the list for you: https://bocianu.gitlab.io/fidl/

 

Here's an image for what I think you want:

 

 

You can adjust blank lines at the bottom/top as required.

 

Export of "BASIC" format is:

 

10000 DATA 70,70,70,48,40,9c,08,08,08,08
10010 DATA 08,08,08,08,08,08,08,08,08,08
10020 DATA 08,08,08,08,08,70,07,07,07,41
10030 DATA 20,9c

 

Edited December 6, 2020 by fenrock
Noticed it was basic needed

[TGB1718]

Also have a look at De-Re-Atari, section 2 give a good description of Display Lists and how to make a custom one.

 

There's also a good section later on if you need DLI's

[+David_P]

When in doubt, cheat.

 

Let BASIC do most of the hard work - call GRAPHICS 3.  Then, using the display list BASIC so generously called from the OS routines for you, search for the first GRAPHICS 0 line in the DL.  Replace it within the DL, and the following line as well, with GRAPHICS 2.  There will be two more GRAPHICS 0 lines; you can replace them with blank scanlines.

 

Or, my Sunday AM without enough coffee attempt at writing it in BASIC:

 

10 GRAPHICS 3

20 DL=PEEK(560)+256*PEEK(561)

30 FOR I=DL TO DL+40

40 IF PEEK(I)<>2 THEN 110

50 POKE I,7

60 POKE I+1,7

70 POKE I+2,0

80 POKE I+3,0

90 POP

100 GOTO 120

110 NEXT I

120 REM YOUR PROGRAM HERE

 

[91SNESplayer]

That’s a really nifty program Fenrock! I tried it out to generate the display list numbers.

However, instead of being greeted by black screen with a blue bar on top, I was greeted by this…

Screenshot from Altirria emulator

 

Here is the program that I used. 

 

5 GRAPHICS 3+16

6 RESTORE

10 DL=PEEK(560)+PEEK(561)*256

20 LET A=0

30 DATA 112,112,112,72,64,156,8,8,8,8,

8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,112,7,65

,32,156

40 FOR R=1 TO 30

50 READ B

60 POKE DL+A,B

70 LET A=A+1

80 NEXT R

90 POKE 87,3

100 COLOR 3

110 PLOT 0,0

120 DRAWTO 39,0

130 GOTO 130

 

Where did I go wrong?

[TGB1718]

Just had a play with this, your problem is where the screen is,

you need to tell the system where it is, here's your modded program, the main part is

to poke the display list with the actual screen address. (I only put the DATA on 2 lines due to the copy/paste into Altirra)

 

5 GRAPHICS 3+16
6 RESTORE 30
10 DL=PEEK(560)+PEEK(561)*256
20 REM LET A=0
30 DATA 112,112,112,72,64,156,8,8,8,8
31 DATA 8,8,8,8,8,8,8,8,8,8,8,8,8,8,8,112,7,65,32,156
40 FOR R=DL TO DL+29
50 READ B
60 POKE DL,B
80 NEXT R
90 POKE 87,3:POKE DL+4,PEEK(88):POKE DL+5,PEEK(89)
100 COLOR 3
110 PLOT 0,0
120 DRAWTO 39,0
130 GOTO 130

[91SNESplayer]

Great! Now just one more thing, how to I properly position and print text in the Graphics 2 “window”?

[TGB1718]

what you need to do (which I forgot) is before the mode 7 line is to put a new

Load Memory Scan instruction to tell the system where the line is located in memory so you need to

add something like 71,(low byte of line), (high byte of line) it can be anywhere in unused memory. 

 

71 is the LMS instruction for a mode 7 line

 

This is from the technical ref Notes

 

 

[Graham Dearsley]

One other thing about Atari BASIC, you don't need the LET. If your program line doesn't start with a keyword then LET is assumed so "10 A=5" will do. If you do use a LET then Atari BASIC will allow you to use a reserved keyword as a variable name but DON'T ?