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PostPosted: Sat Jun 22, 2013 7:57 am 
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Sik wrote:
RGB emphasis can be set separately for each of the components, so it's possible to end with a blue tint (I think there's a game that uses this to make translucent water).

Noah's Ark (E) is one game that does this.

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But yeah, as far as I know that's a PPU register and not something that can be modified from outside (it should affect the signal the PPU itself generates), so messing with the PCB shouldn't cause emphasis to kick in. Probably something else screwed up.

Yeah it's unlikely, because even if a bit got corrupted during one PPU_MASK write, most games rewrite this register every frame so the setting wouldn't stay enabled for long.

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PostPosted: Sat Jun 22, 2013 9:05 am 
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Drakon wrote:
Color emphasis makes everything look dark, like it's night time.

When all 3 bits are used, yes. What happens is that on the composite PPU, these bits actually de-emphasize the other colors (i.e. blue emphasis actually darkens red and green to make the blue stand out), so when you set all 3 bits, all 3 colors are de-emphasized equally, making the image darker. On the RGB PPU however, the emphasis bits increase the color components all the way up (i.e. blue emphasis puts blue at the maximum value and doesn't affect the other components), so when you blow all of them up you get white.

Sik wrote:
I think there's a game that uses this to make translucent water

From the top of my head, I can only think of Noah's Ark, which uses blue emphasis in combination with the grayscale bit to create the water effect. They could have used some sprites on the surface (like in the Sonic games - even the ones on the Master system & Game Gear, which have the same sprite limitations as the NES - but I'm sure you know that :lol:) to make it look better though, that black line doesn't look anything like water.


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PostPosted: Sat Jun 22, 2013 9:42 am 
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The Game Gear also has a much narrower screen, for 40% overdraw instead of 25%.

Doesn't Chemical Plant Zone act 2 in Sonic 2 rewrite the palette for the parts under polluted water? The NES can't really do that.


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PostPosted: Sat Jun 22, 2013 10:51 am 
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tepples wrote:
The Game Gear also has a much narrower screen, for 40% overdraw instead of 25%.

Sure, but the same games are on the Master System (OK, not Triple Trouble - officially at least), which has a display as wide as the NES.

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Doesn't Chemical Plant Zone act 2 in Sonic 2 rewrite the palette for the parts under polluted water? The NES can't really do that.

The great majority of water levels in Sonic games rewrite the palette. The one exception I can think of is the beginning of Hydrocity Act 1 in Sonic 3, because of the "water filling up the tunnel" gimmick. As for the 8-bit games, I'm fairly sure Sonic 1 and 2 on the SMS/GG also didn't rewrite palettes, but Chaos, Triple Trouble and Blast did.

Anyway, I was only questioning what Noah's Ark does for the surface of the water (black line?), what it does for the actual water is fine IMO (the grayscale bit makes the things look pretty bright though, but I understand that the blue emphasis alone without any sort of effect on the surface would have been too subtle), it doesn't need to rewrite the palette.


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PostPosted: Sat Jun 22, 2013 2:36 pm 
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mikejmoffitt wrote:
Just curious, do we have a database of games that use color emphasis? I've just never known if I am seeing it or not on a game; I don't think I've seen it enough to really know ...

A very good question and point. No, we do not have such a "database" -- and I hate the use of that word in this context (would prefer "a list of games that use it") -- so I have created exactly that:

http://wiki.nesdev.com/w/index.php/Colo ... asis_games

I urge folks to update this with games they know use the bits, and to please add short descriptions where in-game they're used; if you aren't sure what to say/how to say it, use the Tricky-to-emulate games page as a guide.

I also added a link to this in the NES reference guide section, as appropriate.


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PostPosted: Sat Jun 22, 2013 4:05 pm 
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You're missing at least Magician, Jungle Book and Lion King (I think both the official and pirate versions).


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PostPosted: Sat Jun 22, 2013 4:07 pm 
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Didn't James Bond Jr. use all 3 bits like, the whole time just to darken the entire screen?


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PostPosted: Sat Jun 22, 2013 5:21 pm 
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Grapeshot wrote:
You're missing at least Magician, Jungle Book and Lion King (I think both the official and pirate versions).

I'm not missing anything -- it's a wiki, which is why I urged folks to update it. :D


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PostPosted: Sat Jun 22, 2013 6:48 pm 
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Didn't realize that account creation was enabled again on the wiki.


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PostPosted: Sat Jun 22, 2013 10:07 pm 
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No way these $2001 writes could be filtered with some added hardware so that the top 3 bits were never set? D7 to PPU = D7 from CPU AND (address lines to PPU aren't 001)?


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PostPosted: Sat Jun 22, 2013 11:49 pm 
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blargg wrote:
No way these $2001 writes could be filtered with some added hardware so that the top 3 bits were never set? D7 to PPU = D7 from CPU AND (address lines to PPU aren't 001)?

A device similar to a Game Genie? I guess it could work...


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PostPosted: Sun Jun 23, 2013 5:47 am 
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blargg wrote:
No way these $2001 writes could be filtered with some added hardware so that the top 3 bits were never set? D7 to PPU = D7 from CPU AND (address lines to PPU aren't 001)?

That would be a cool device if it's not a pain to make. For now I'm content with romhacking. Yesterday I mentioned this to spikeman and handed him my progress. Spikeman went into turbo spikeman mode and fixed the brightman stage. According to the original author of this hack dr cossack stage 3 lower route also has color emphasis which it does in a playthrough video I found. I'm unsure if our current fix also fixed cossack stage 3 I'm waiting for someone to play to that stage in fceux and make a savestate we can use for debugging.


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PostPosted: Sun Jun 23, 2013 11:52 am 
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blargg wrote:
No way these $2001 writes could be filtered with some added hardware so that the top 3 bits were never set? D7 to PPU = D7 from CPU AND (address lines to PPU aren't 001)?
If you're willing to rely on bus conflicts, sure!

Use a 74'238 (active high one-of-eight selector) and 74'03 (open collector quad NAND) to make this:

M2 → 238.+G1
A15 → 238./G2A
A14 → 238./G2B
A2 → 238.C
A1 → 238.B
A13 NAND A0 → 238.A (use pull-up resistor)
238./Y0 NAND self → D7
238./Y0 NAND self → D6
238./Y0 NAND self → D5


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PostPosted: Mon Jun 24, 2013 8:45 am 
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After using spikeman romhacking + game genie codes I got to the spot in cossack stage 3 with color emphasis. I sent spikeman the savestate, he found the data, and it's changed. I wound up changing the rising / falling water from emphasis to grayscale. In the brightman stage the areas that you can't see are also changed from emphasis to grayscale. I burned the rom, plugged it into my mmc5 devcart, runs great on my rgb twin. I think this is done unless we find another part of the game that uses color emphasis. The author of this romhack only mentioned these two stages.


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PostPosted: Mon Jun 24, 2013 1:28 pm 
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thefox wrote:
Sik wrote:
RGB emphasis can be set separately for each of the components, so it's possible to end with a blue tint (I think there's a game that uses this to make translucent water).

Noah's Ark (E) is one game that does this.

Quote:
But yeah, as far as I know that's a PPU register and not something that can be modified from outside (it should affect the signal the PPU itself generates), so messing with the PCB shouldn't cause emphasis to kick in. Probably something else screwed up.

Yeah it's unlikely, because even if a bit got corrupted during one PPU_MASK write, most games rewrite this register every frame so the setting wouldn't stay enabled for long.


I am pretty sure that this is what I caused to happen, though. Here is a video of it happening by briefly touching a capacitor to a CPU pin(You can see it kick in at 0:33 right before the game crashes). If I find it, I have a video of a Famicom starting to act strange if I mash my palm on the underside of the PCB. It starts with the tint changing, the sync starting to waver, the jailbars becoming more pronounced, followed by usually a game crash, but occasionally just weird mis-writes that don't break it completely.


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