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PostPosted: Sun Nov 20, 2005 4:13 am 
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It was discussed a while back, on the old forums.
http://nesdev.com/cgi-bin/wwwthreads/showpost.pl?Board=nesdev&Number=1312

Here's the (old) source, if anyone wants the newer version let me know and I'll retest it. I think it mostly worked at that point, but was slightly broke.
http://mywebpages.comcast.net/memblers/fautest.zip
latest test version (July 2004):
http://mywebpages.comcast.net/memblers/fau.nes

There's not enough time in hblank to do much, so it shuts the screen off early. Even then, since it has to set and reset $2006 and $2005 there's only enough time for one $2007 write. If it blanked every odd scanline and displayed the even ones it could change the palette a lot more, I bet. Though it would halve the vertical resolution and put in horizontal bars..

So the current code for each scanline switches between changing a palette entry and changing an attribute byte. Changing the attribute byte like this was supposed to allow for more color varations. But I don't know if that part of the program even worked (the test data doesn't seem to do much with it).


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PostPosted: Sun Nov 20, 2005 11:23 am 
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Man, this looks to be damn OLD !!! Before I even enteren in NESDev scene.
I remember trying to understand how your FAU works, and I never got it at all. What advantages does it exactly features ? More colors, but how exactly ? What's up with attribute tables, I can't see much interest by modifying them ? Will gabarage show up on the rightmost border of the screen ? How fine works to set-up scrooling regs every scanline ?
How could this format be used in an actual game ? To enhance portrait or cutscenes ? Could this be converted to work on a PAL system ?

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PostPosted: Sun Nov 20, 2005 11:27 am 
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Hrm... I take it it's not supposed to jerk around like it does in my emu and Nintendulator?


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PostPosted: Sun Nov 20, 2005 12:26 pm 
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I'm particulary interested in the "blank every odd scanline" thing. The blank lines are not such an ugly thing to look at, and a full scanline will give you enough time to change all the palettes, I suppose. 13 unique colors per scanline! Can you imagine that? The images would look great. Of course, we'd still have the limitation where every run of 16 pixels has to share the same palette, and the ammount of data needed for such a picture would be huge.

Maybe if we cut some of the left AND right side of the screen (without the blank lines) we'd be able to change 1 full palette, that would be great. It seems useless for the in-game parts, but is very usefull for cutscenes.


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PostPosted: Sun Nov 20, 2005 12:58 pm 
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I'd imagine writing to the palette mid-frame would be difficult, since when the PPU is off and the PPU address is in the palette range (3Fxx) it will render whatever color is stored at the current address (not always the color at 3F00)


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PostPosted: Sun Nov 20, 2005 1:23 pm 
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Oh yeah... I forgot about that detail... so, no blank scanlines!


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PostPosted: Sun Nov 20, 2005 10:37 pm 
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The effect would be useful for a game if it was simplified more, actually I was inspired by Chris C.'s stretch demo to make a racing game with ramps, hills, mountains.. heheh. The trick lets you scale the background vertically. That got me wanting to figure out how to use $2006 mid-frame without glitches. I never wrote any of that game though, just the FAU-mode test. The palette and attrib table changing was just to see how far I could push it.

see the fau.txt file in the zip for what I wrote about it, it's not real useful though.

The attribute thing was supposed to allow certain blocks to be as small as 16x2.

Yeah, there is some garbage on the right border. You can see the variations in the timing, and also there's a black comb-like thing on the edge.

I think it does jerk around sometimes on a real NES. Resetting would fix or break it, I can't recall if I fixed that in the last version.


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PostPosted: Mon Nov 21, 2005 11:38 am 
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This remember how the text boxes work in the SNES game Tales of Phantaia, where the SNES background color is changed every sacnline with a tricky trick. In menu, there is sometimes some more tricky tricks combinating transparent sprites and background color to allow this effect only available on a small horizontal block of the screen.

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