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Old 01 September 2019, 19:24   #1
Retro1234
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256x224 MegaDrive and Snes

When games on the MegaDrive or Snes used 256*224 mode were they stretched horizontaly to fill the full width of the screen 320?

If yes why couldn't Amiga games like Toki that have a fairly small Horizontal width employee a similar technique to make the playing area appear larger?

this is a interesting video on the subject [ Show youtube player ]
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Old 01 September 2019, 20:12   #2
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Yep, this is why some SNES games look like crap if the developers didn’t design with this in mind during development i.e Super Mario World and Yoshi’s Island.

And yes this is something i did wonder about in the past, using hardware like the sdbl mode for doubling vertical pixels for cdxl video in the AA chipset, i know horizontal is different and i don’t know if its possible if its not built into the video display hardware, something computers didn’t really have due to monitors and 8-bit computers had the infamous borders around the screen, something Commodore should have included at the very least on its games console, i mean Chaos Engine is in a much higher resolution than the SNES one but looks worse side by side on a large screen because of the awful black screen estate.
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Old 01 September 2019, 20:59   #3
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Originally Posted by Retro1234 View Post
If yes why couldn't Amiga games like Toki that have a fairly small Horizontal width employee a similar technique to make the playing area appear larger?
No.
Amiga cannot stretch pixels because output is a fixed (sub)multiple of master clock (28.375160 MHz, PAL).
lores/hires/shires are multiple of this frequency, respectively /4, /2, /1.

Technicalities:
MD system master clock rate: 53.693175 MHz (NTSC), 53.203424 MHz (PAL)[
"H32"(256px) pixel clock = Master Clock / 10 = 5.3693175 Mhz (NTSC) or 5.3203424 Mhz (PAL)
"H40"(320px) pixel clock = Master Clock / 8 = 6.711646875 Mhz (NTSC) or 6.650428 Mhz (PAL)

So even at the 320px resolution, the pixel is wider than that of the Amiga.
A field large 320px on the console occupy the same 'space' of an Amiga overscanned screen.
Precisely 320*(7.093790/6.650428)= ~341 pixels.

Similar for SNES with two selectable frequency derived from master clock (21.28137 MHz, PAL))
"256x" pixel clock = Master Clock / 4 = 5.3203425 Mhz (PAL)
"512x" pixel clock = Master Clock / 2 = 10.640685 Mhz (PAL)
So also in this case the 256x occupy as an overscanned ~341px Amiga screen.

The consoles are designed just for gaming so it makes sense to create wider pixels to completely fill the screen (and use less pixels to speed-up operations).
The situation is different on home computers where a full 40c/80c terminal was the norm (without hidden pixels).
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Old 01 September 2019, 21:07   #4
Retro1234
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I have no idea what you what you just said Ross but I take your word for it

Shame obviously you can stretch a 200 vertical screen my choosing NTSC just wondered if it was possible horizontaly O well

@AmigaJay Chaos Engine CD32 is full screen in NTSC
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Old 01 September 2019, 21:12   #5
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To boil down ross's explanation into a single word... "no"

Which is why if you want to see a pixel perfect conversion of many 1980's arcade classics, you will end up with borders .... 256x224 is a very common screen resolution for arcade games back then (Black Tiger etc..)

Last edited by lilalurl; 01 September 2019 at 21:48.
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Old 01 September 2019, 22:20   #6
ross
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I have no idea what you what you just said Ross but I take your word for it

I forgot it but there is also a even lower resolution in Amiga which is the "hicolors copper-chunky mode" where the 'pixel' is at copper registers update frequency (lores/8) i.e. ~47px overscan.
A bit too low I think


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To boil down ross's explanation into a single word... "no"
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Old 02 September 2019, 03:09   #7
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I forgot it but there is also a even lower resolution in Amiga which is the "hicolors copper-chunky mode"
I could swear that I have seen some kind of artifact when using DBLPAL that seems to give you a 160x wide screen? Or is my memory totally shot?

For shits and giggles, load up PicCon and import a 256 wide picture and use the convert to SNES option.
Bascially showing superhires with 5 pixels repeated.
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Old 02 September 2019, 10:55   #8
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I could swear that I have seen some kind of artifact when using DBLPAL that seems to give you a 160x wide screen? Or is my memory totally shot?
I don't know how but you never know

Quote:
For shits and giggles, load up PicCon and import a 256 wide picture and use the convert to SNES option.
Bascially showing superhires with 5 pixels repeated.
Yep, the shres is used for tricks like that, there are demos that use it to do interesting things.
Unfortunately only AGA, difficult to manage and uses too much DMA
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Old 02 September 2019, 11:22   #9
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I could swear that I have seen some kind of artifact when using DBLPAL that seems to give you a 160x wide screen? Or is my memory totally shot?

For shits and giggles, load up PicCon and import a 256 wide picture and use the convert to SNES option.
Bascially showing superhires with 5 pixels repeated.
With double kHz modes, like DBLPAL, and VGA you need to set superhires bit on for 640x512@50 Hz and 640x480 @ 60 Hz. When using 640x256 and 640x240 you still need to have superhires bit on, and the system uses the other modulo register to repeat vertical lines twice. These modes are a real waste of bandwidth.

When we go to 320x256 and 320x240 with double kHz modes, you need to set hires bit and system uses other modulo register again to show double lines. Waste of bandwidth again.

So there is still lores bit left, and this gives 160x256 and 160x240 resolutions with double repeated vertical lines. You can also use 320x512 and 320x480, and 160x512 and 160x480 without repeat modulo.

So yes, resolutions like 160x256 and 160x240 are available under AGA, but they are not PAL modes.
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