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Pixel 250->256 change
http://forums.nesdev.com/viewtopic.php?f=3&t=9690
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Author:  tepples [ Sat Jan 12, 2013 8:52 pm ]
Post subject:  Re: Pixel 250->256 change

I've used the terminology "at x=256". Is that unambiguous?

Author:  tokumaru [ Sat Jan 12, 2013 10:01 pm ]
Post subject:  Re: Pixel 250->256 change

tepples wrote:
I've used the terminology "at x=256". Is that unambiguous?

That would be the 257th pixel, right?

Author:  rainwarrior [ Sat Jan 12, 2013 10:38 pm ]
Post subject:  Re: Pixel 250->256 change

I kinda wondered why we didn't start numbering at the left edge of the screen/signal. I don't know exactly what clock it's on, but there's a region at the start of the line before it starts rendering any sprite or nametable pixels that it will output the background colour.

Author:  tepples [ Sat Jan 12, 2013 11:03 pm ]
Post subject:  Re: Pixel 250->256 change

Probably because the earliest we can detect within the scanline with sprite 0 is x=0 (the first rendered pixel).

Author:  Dwedit [ Sun Jan 13, 2013 3:52 am ]
Post subject:  Re: Pixel 250->256 change

Because of NMI, that's what defined pixel 0.

Author:  thefox [ Sun Jan 13, 2013 4:15 am ]
Post subject:  Re: Pixel 250->256 change

Yeah, the left border of the very first rendered scanline is the hblank of the pre-render scanline.

Author:  Zepper [ Sun Jan 13, 2013 6:52 am ]
Post subject:  Re: Pixel 250->256 change

That's the point I disagree. Anyway, here my last $0.02:

a) Is there a special reason for using the word "dot" instead of "cycle"?
b) The word "pixel" would count effective pixels from 1, and not from zero.

I suggest to abandon the usage of "dot" as "ppu cycles"; just "cycle" is good enough, and it counts from zero. When saying "pixel", it's always from 1.

tepples wrote:
I've used the terminology "at x=256". Is that unambiguous?


Since x can be zero, you mean the 257th rendered pixel.

Author:  tepples [ Sun Jan 13, 2013 7:16 am ]
Post subject:  Re: Pixel 250->256 change

Does "cycle" refer to CPU cycles (1.8 MHz), PPU cycles (5.4 MHz), or master clock cycles (21.5 MHz)? "Dot" is less ambiguous. I seem to remember someone finally nailing down the terminology as "cycles" for the CPU, "dots" or "pixels" for the PPU, and "clocks" for the master clock. As for "dot" vs. "pixel", I'll look into that too.

EDIT: It was this post by blargg.
The term "dot clock" is used in an X server HOWTO.

Author:  blargg [ Sun Jan 13, 2013 10:14 am ]
Post subject:  Re: Pixel 250->256 change

To me dots are the timebase of the PPU, while pixels are the dots that actually paint something on screen, though I suppose that the video signal is always outputting something for every dot, like the background color, or the sync pulse. I think most people refer to only 256 of the 341 dots of a scanline as pixels.

The benefit of "dot" over "ppu cycle" is that the latter is more verbose, not entirely clear, and will be shortened to "cycle" in discussion, which might then be confused with the CPU.

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