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Hello again;

This is a quick-and-dirty test to try to get extra sprite colors by changing palettes between scanlines.

I probably won't use it for anything, but here it is, in case somebody is interested. :P

Github link: https://github.com/haroldo-ok/rpg-battle-poc

rpg_battle.png (1.62 KB)

Screenshot

rpg_battle-0.1.sms.zip (3.97 KB)

The ROM for version 0.1

rpg-battle-poc-0.1.src.zip (22.16 KB)

Source code for version 0.1

haroldoop wrote

Hello again;

This is a quick-and-dirty test to try to get extra sprite colors by changing palettes between scanlines.

I probably won't use it for anything, but here it is, in case somebody is interested. :P

Fera!

haroldoop wrote

Hello again;

This is a quick-and-dirty test to try to get extra sprite colors by changing palettes between scanlines.

I probably won't use it for anything, but here it is, in case somebody is interested. :P

How many Z80 cycles are there between scanlines. For some reason, when I heard that you could move the scanline right or left during this short time gap, I'd assumed that couldn't also color cycle nor do anything else useful at the same time.

I've been coming up with ideas for improving color, but I didn't know if there was enough time between lines.

Horizontal interrupts are quite inefficient, they fire early (or is it late?) so you have to waste a few cycles to align to the offscreen area, and then I think you only have time to update two colours per line without causing cram dots to be visible in the active area.

Maxim wrote

Horizontal interrupts are quite inefficient, they fire early (or is it late?) so you have to waste a few cycles to align to the offscreen area, and then I think you only have time to update two colours per line without causing cram dots to be visible in the active area.

So, in theory, with some really tight timing, someone cold change all of the 16 sprite colors in a spread of 8 scanlines with no visual artifacts?

I think so, yes. It’s not very practical though as there sprites have to avoid each other vertically :) but could be useful for a status area or split screen game.

Quote

So, in theory, with some really tight timing, someone could change all of the 16 sprite colors in a spread of 8 scanlines with no visual artifacts?

It's good to change the color palette, and that's occasionally needed (especially for color swapping to get flowing waterfalls, lava, animation, etc.), but the more important one is moving that horizontal line at a different rate than its contemporaries, giving us that all important parallax effect.

I'd also thought of using that interlude to update the audio, which can be done at 15.7KHz if done at the end of every scanline. That doesn't really need an interrupt sent to the processor, but it seemed handy, if the overhead of a line interrupt is to be accepted anyway.

We have only 60,000 cycles per frame and just 310 Z80A cycles per line, IIRC. Accounting for the line interrupt overhead, that only allows a couple of subroutines running about 60-100 instructions per line, depending on how the code is written.

Author	Message
haroldoop Joined: 25 Feb 2006 Posts: 874 Location: Belo Horizonte, MG, Brazil	Quick-and-dirty P.O.C. changing palettes between scanlines for extra sprite colors Posted: Fri Mar 04, 2022 11:57 pm Last edited by haroldoop on Sat Mar 05, 2022 9:32 am; edited 1 time in total
	Hello again; This is a quick-and-dirty test to try to get extra sprite colors by changing palettes between scanlines. I probably won't use it for anything, but here it is, in case somebody is interested. :P Github link: https://github.com/haroldo-ok/rpg-battle-poc rpg_battle.png (1.62 KB) Screenshot rpg_battle-0.1.sms.zip (3.97 KB) The ROM for version 0.1 rpg-battle-poc-0.1.src.zip (22.16 KB) Source code for version 0.1

EmuBoarding Joined: 06 Aug 2015 Posts: 149	Posted: Sat Mar 05, 2022 1:17 am
EmuBoarding Joined: 06 Aug 2015 Posts: 149	haroldoop wrote Hello again; This is a quick-and-dirty test to try to get extra sprite colors by changing palettes between scanlines. I probably won't use it for anything, but here it is, in case somebody is interested. :P Fera!

maxxoccupancy Joined: 05 Mar 2022 Posts: 129 Location: Seabrook, New Hampshire	Posted: Sat Mar 05, 2022 4:43 am
	haroldoop wrote Hello again; This is a quick-and-dirty test to try to get extra sprite colors by changing palettes between scanlines. I probably won't use it for anything, but here it is, in case somebody is interested. :P How many Z80 cycles are there between scanlines. For some reason, when I heard that you could move the scanline right or left during this short time gap, I'd assumed that couldn't also color cycle nor do anything else useful at the same time. I've been coming up with ideas for improving color, but I didn't know if there was enough time between lines.

Maxim Site Admin Joined: 19 Oct 1999 Posts: 14745 Location: London	Posted: Sat Mar 05, 2022 7:35 am
	Horizontal interrupts are quite inefficient, they fire early (or is it late?) so you have to waste a few cycles to align to the offscreen area, and then I think you only have time to update two colours per line without causing cram dots to be visible in the active area.

haroldoop Joined: 25 Feb 2006 Posts: 874 Location: Belo Horizonte, MG, Brazil	Posted: Sat Mar 05, 2022 11:13 am
	Maxim wrote Horizontal interrupts are quite inefficient, they fire early (or is it late?) so you have to waste a few cycles to align to the offscreen area, and then I think you only have time to update two colours per line without causing cram dots to be visible in the active area. So, in theory, with some really tight timing, someone cold change all of the 16 sprite colors in a spread of 8 scanlines with no visual artifacts?

Maxim Site Admin Joined: 19 Oct 1999 Posts: 14745 Location: London	Posted: Sat Mar 05, 2022 6:48 pm
	I think so, yes. It’s not very practical though as there sprites have to avoid each other vertically :) but could be useful for a status area or split screen game.

maxxoccupancy Joined: 05 Mar 2022 Posts: 129 Location: Seabrook, New Hampshire	Posted: Sat Mar 05, 2022 10:14 pm
	Quote So, in theory, with some really tight timing, someone could change all of the 16 sprite colors in a spread of 8 scanlines with no visual artifacts? It's good to change the color palette, and that's occasionally needed (especially for color swapping to get flowing waterfalls, lava, animation, etc.), but the more important one is moving that horizontal line at a different rate than its contemporaries, giving us that all important parallax effect. I'd also thought of using that interlude to update the audio, which can be done at 15.7KHz if done at the end of every scanline. That doesn't really need an interrupt sent to the processor, but it seemed handy, if the overhead of a line interrupt is to be accepted anyway. We have only 60,000 cycles per frame and just 310 Z80A cycles per line, IIRC. Accounting for the line interrupt overhead, that only allows a couple of subroutines running about 60-100 instructions per line, depending on how the code is written.

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