11 January 2009, 00:13 | #1 |
Registered User
Join Date: Mar 2008
Location: Poland
Posts: 159
|
Swiv undocumented score feature
This question seems to be addressed to Toni.
Swiv uses 4-plane display (16 colours) except the scan lines where the score is displayed. During lines $34-$3A the 5th bitplane is switched on. But it's not ordinary 32-colour display. When a bit in the 5th plane is set the output colour is colour #16 regardless of the bits in planes 1-4. The question is: what are the conditions to achieve such display? I can't find anything relevant: bplcon0 = $5200 ($4200 outside lines $34-$3A), bplcon1 = $0000 and bplcon2 = $003F |
11 January 2009, 09:29 | #2 |
WinUAE developer
Join Date: Aug 2001
Location: Hämeenlinna/Finland
Age: 49
Posts: 26,570
|
It happens when BPLCON2 has "illegal" priority value, http://eab.abime.net/showpost.php?p=206345&postcount=5
|
11 January 2009, 12:21 | #3 |
Registered User
Join Date: Mar 2008
Location: Poland
Posts: 159
|
Thanks. I was searching for that post but couldn't find it.
|
22 January 2009, 03:18 | #4 |
FPGAmiga rulez!
Join Date: Dec 2007
Location: South of France
Age: 50
Posts: 155
|
|
22 January 2009, 13:24 | #5 |
Registered User
Join Date: Mar 2008
Location: Poland
Posts: 159
|
That's why I was asking. But haven't done it yet.
|
23 January 2009, 01:58 | #6 |
Registered User
Join Date: Apr 2006
Location: Sydney / Australia
Posts: 113
|
Nifty trick.
I'm wondering, suppose you wanted to create this effect but you couldn't use this bug. How would you go about it? Is there a better way than blitting it onto the 4 regular bitplanes, which would be a PITA when the screen scrolls and you need to restore those sections of the planes... Just curious... |
23 January 2009, 05:17 | #7 |
Join Date: Jul 2008
Location: Sweden
Posts: 2,269
|
If you're not using sprites in that part of the screen you could just set the upper 16 colors in the palette to the same value, and change them all on each line (if there's enough time) if you want the same coloring effect as in SWIV.
|
23 January 2009, 08:15 | #8 | |
WinUAE developer
Join Date: Aug 2001
Location: Hämeenlinna/Finland
Age: 49
Posts: 26,570
|
Quote:
Last edited by Graham Humphrey; 23 January 2009 at 09:51. Reason: Fixed quote tag |
|
07 March 2017, 20:16 | #9 | ||
Registered User
Join Date: Sep 2015
Location: Germany
Posts: 260
|
Quote:
Quote:
As I learned from Toni's post, Agnus and Denise behave different, if we have BPU>6. What about Alice and Lisa. Do they have the same behaviour if BPU>8? The next question is, why the BPLCON2-trick and the 7th-plane-trick don't work on the AGA chipset. Is it only because the number of planes has been increased upto 8 with four BPU0-3-bits? For the 7th-plane-trick this is obvious but also for the BPLCON2-trick? It would be interesting what really happens here, if PF2P>5. What is the logic behind it? And even more interesting, how did the programmers found out this effect for SWIV in 1991? They seemd to be the second ones, as Kefrens already used this trick in their Megademo7/Dragons-Part in 1989. They also worked with the value $3f for BPLCON2. I suppose this "error" wasn't removed by the designers of the AGA chipset. This means that it could still work, if we adapt this logic to a higher number of planes. What do you think about this, Toni? |
||
07 March 2017, 20:35 | #10 |
WinUAE developer
Join Date: Aug 2001
Location: Hämeenlinna/Finland
Age: 49
Posts: 26,570
|
It does not work in AGA. Also >8 planes = confirmed to always cause blank screen (= 0 planes)
|
Currently Active Users Viewing This Thread: 1 (0 members and 1 guests) | |
Thread Tools | |
Similar Threads | ||||
Thread | Thread Starter | Forum | Replies | Last Post |
Undocumented Amiga hardware stuff | Toni Wilen | Coders. Asm / Hardware | 342 | 09 June 2024 23:02 |
Action Replay Undocumented Features | deicidal | support.Hardware | 0 | 01 March 2010 17:15 |
EAB's High Score Chase : SWIV | TCD | EAB's competition | 25 | 20 September 2009 22:41 |
SWIV-feature request | Bamiga2002 | project.WHDLoad | 0 | 22 March 2008 09:40 |
Games missing high score saving feature | Shoonay | project.WHDLoad | 5 | 21 May 2006 18:56 |
|
|