Three Gfxs Modes 'GTIA Bug' on the same scanline(s) an idea...

[José Pereira]

The called 'GTIA Bug' like we have here on this screen in the Middle scanlines:

http://a8.fandal.cz/detail.php?files_id=6111

If I have an idea for a game that would have something around 192 scanlines use and:

LEFT SIDE: 8Bytes GR.8 hi-resolution Logo

MIDDLE PART: 24Bytes low-resolution GTIA Mode Playing Area

RIGHT SIDE: 8Bytes middle-resolution GR.15 Status Panel

What cpu would I have left to have some guys moving on the middle part GTIA Mode (static screen and no scrolling)?

If any free to use then the moving guys have to be PMGs only or 3, 4 small software sprites would be also be possible?

Edited September 4, 2013 by José Pereira

[Rybags]

For the part of the screen where the 3 modes is wanted, much of the CPU is tied up in doing the changes.

Most demos that do this switching just use a loop and waste the surplus cycles during the required time.

 

For a game it might be possible to interleave some of the game code with the mode change stuff, it would make for a bloated program that uses a lot of memory comparitive to what's needed but it can make use of some otherwise wasted cycles.

 

But even then the available cycles vs a standard graphics mode will still be significantly less so softsprite usage would have to be reduced.

[José Pereira]

Rybags just got what I want:

That screen using dimensions and moving stuff as PMGs only like this:

GUY1: P0+P1 Multicolour 3colours

GUY2: P2+P3 Multicolour 3colours

SHOT1: M0+M1 5th Player

SHOT2: M2+M3 5th Player

 

This way possible?

 

And there is an exact number of Bytes width for each one the three gfxs modes (here it seems the side ones have 10Bytes each but on mine I want them to have 8Bytes)?

Edited September 4, 2013 by José Pereira

[Creature XL]

The called 'GTIA Bug' like we have here on this screen in the Middle scanlines:

http://a8.fandal.cz/detail.php?files_id=6111

If I have an idea for a game that would have something around 192 scanlines use and:

LEFT SIDE: 8Bytes GR.8 hi-resolution Logo

MIDDLE PART: 24Bytes low-resolution GTIA Mode Playing Area

RIGHT SIDE: 8Bytes middle-resolution GR.15 Status Panel

What cpu would I have left to have some guys moving on the middle part GTIA Mode (static screen and no scrolling)?

If any free to use then the moving guys have to be PMGs only or 3, 4 small software sprites would be also be possible?

 

Wh yno tuse the titlepic of "Cave Heli" as an example? Kidding, Exin intenitionally left the GITA area black.

 

@topic

As Rybags said, the 192 scan-liones are more or less wasted. As you might want to change the color as well.

You might be able to color the PMG 2600-style.

 

Your effective ccles per frame would be (assuming PAL and blank lines other then the 192):

 

(312-192)*114=13680 cylces. Could be around C64 speed

As an example, a generic soft-sprite rouitne for 9x16 sprites takes around 1500 cycles.

 

As game logic must not be frame exact you should be able to make a game with it. A curern texample is the colision detection in "Heli Cave".

This runs in teh main loop, if there is time. So a very low percentage of collisions goes unnoticed. But better then a system crash. And then again, in real life bullets do not hit there target in every case either

 

 

 

EDIT:

The C64 has more then I thought:

 

 

http://www.lemon64.com/forum/viewtopic.php?t=2629&sid=39761578d872f12da4ce6b4d7d064234

The PAL C64 has 312 scanlines giving 63*312 = 19656 cycles. If the display is activated (without sprites), the VIC will steal 40 cycles for each badline which gives us 63*312 - (25*40) = 18656 cycles. Add some sprites and the free cycles will decrease even more.

 

Edited September 4, 2013 by Creature XL

[Rybags]

You have some scope as to where the mode changes can occur but the refresh and DMA cycle steals from Antic puts some extra limitation on them.

[Creature XL]

One IMPORTANT note!

As mentioned the title pic is in the mode you want to use for your game.

On one of my 800XLs the "GTIA area" got messed up after the XL run for 1 minute or so. So I guess it has to do with its temperatur.

If I turn it off, wait some seconds/minutes. Turn it on, the pic displayed Ok for some seconds. Then it went garbage again.

As your playfield is in this area, the game would be unplayable for me (and maybe others ).

 

 

Second note, you migh tknow the color register get shifted. Luckily this was fixed in G2F as far as I know

As far as I recall its like this:

PF0->PF1

PF1->PF2

...

COLBK->PF0

 

you can read the details in the Altirra HW-manual (as always)

Edited September 4, 2013 by Creature XL

[Tezz]

When I did the Chimera loading pic a few years ago, checking it on my 130XE there was a small glimmer in one part of the GTIA area. I'd be interested if anyone could check it out running on their machine.

chimera_n33.xex

[TMR]

If by "glimmer" you mean something constantly changing, i'm not seeing that on my 800XL here but i do have something closer to what A8Win produces than a perfect image like Altirra produces; on my screen, the longest vertical white line has a "hiccup" on it where the prow of the ship is and there's a black line mirroring it over the planet. What appears as white areas on the planet to the right of the white lines above that largest one come out as black:

 

 

Please excuse the terrible photo. =-)

[Tezz]

If by "glimmer" you mean something constantly changing, i'm not seeing that on my 800XL here but i do have something closer to what A8Win produces than a perfect image like Altirra produces; on my screen, the longest vertical white line has a "hiccup" on it where the prow of the ship is and there's a black line mirroring it over the planet. What appears as white areas on the planet to the right of the white lines above that largest one come out as black:

 

Chimera - bad grab.jpg

 

Please excuse the terrible photo. =-)

Thanks Jason, yes on my xe it had a slight glimmering flicker at one of the mode changes. ...I remember now that I'm home that I talked about it at the time with Avery (Feb 2011) and he kindly checked the results between emulation and a real 800xl and 130xe sending back some photos and the timing was then sorted in later builds. With the latest Altirra build it does show the image as it's displayed on the 800xl with those white lines. At the time g2f didn't visualise the raster changes so I was relying on emulation whilst I was working on it. Interesting to see that your XL displayed the black lines in the planet like the xe whareas Avery's xl didn't.

Edited September 4, 2013 by Tezz

[José Pereira]

Explain you've sirs whats in here but the start and idea is here:

 

 

Or I can explain you now.

This is an Arkanoid type but the same way GTIA Modes without the GTIA Bug I couldn't do the same way but it wouldn´t look so good/beautifull I think!...

Like I did and had the idea at X:8 with the mixing of Hi-Resolution and Middle Resolution then this is the another idea from me.

Maybe another crazy that ask first...

The center part is in GR.11 with the 'VAUS' beeing P0+P1 and P2+P3 Multicolour the two. We can have two ballls represented by those white balls as 5th Player 2Missiles in each ball taking the non-existance PF3 Colour Register.

If my DLIs at the Left side Hi-Resolution and the Right side GR.15 Bitmap Graphics Mode 3+1colours maybe too much then I would suggest that if anyone interested I could change this into none blocks 'Arkanoid type´and turn this into a Pong type with two Players isometric (each one moving top/bottom and isometric left and right)-

I think that maybe there's not much/any cpu to get those 3D/Isometric Blocks but we could be aware of this and just turn this into a Pong/squash game.

What do you you say?

Edited September 5, 2013 by José Pereira

[José Pereira]

P.s.- I asked first and this screen is based on the 'GTIA Bug idea' but it's amix of G2F/Emulators with PAINT P.C. Windows program.

The question and the meaning of this Topic/Thread is we can discuss/talking about this.

Thanks.

Greetings.

José Pereira.

[Heaven/TQA]

As long as you can squeeze the game logic into VBL timing there should be no problem with the 3 mode screen... CPU is locked for the screen Area but rest it can do the game?

[+Stephen]

It looks awesome! Similar to what Breakout 2000 was on the Jaguar. That game played at about 12fps (normal for the Jag - LOL). That would give you 5 frames to handle the logic, etc.

[Synthpopalooza]

An idea: How would the game look using Graphics 10?

 

To do this, you would have to hard code the graphics so that color pattern #1000 is used where the background would be. This would enable PMG's to work correctly. Also you need to use PF0-PF3 (color patterns #0100 to #0111) for the areas where you want the ball to show up. Maybe use PM colors #0000 to #0011 for the blocks.

 

This will also cause some banding at the top and bottom of the screen, there will be a band showing in the color of PM0 (which is the BG color in graphics 10).

[Rybags]

Looks good - the iso view helps to conceal the low horizontal resolution. And the game logic for a Breakout type affair is very minimal CPU requirement (a Breakout game was like my second or third game ever on the Atari).