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Old 02 July 2019, 16:03   #1
rsn8887
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Maximum number of Amiga scanlines?

What is the maximum number of scanlines the Amiga can display?

I am asking because Babeanoid just surprised me by displaying content on more than 270 scanlines.
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Old 02 July 2019, 16:31   #2
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Originally Posted by rsn8887 View Post
What is the maximum number of scanlines the Amiga can display?

I am asking because Babeanoid just surprised me by displaying content on more than 270 scanlines.
The question is incomplete because Amiga can display a variable number of lines.

If you are talking about a simple Amiga OCS in standard progressive PAL mode then the answer is 286 lines with visible data.
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Old 02 July 2019, 17:16   #3
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Thanks. I found another post here: http://eab.abime.net/showpost.php?p=565709&postcount=13

The maximum is 384x288 according to that post
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Old 02 July 2019, 18:24   #4
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Thanks. I found another post here: http://eab.abime.net/showpost.php?p=565709&postcount=13

The maximum is 384x288 according to that post
This is incorrect.

384x288 is only a theoretical PAL resolution, valid if we use exactly 50 lines for the vertical blank when interlaced
(therefore 25 lines in progressive mode) and 313 progressive lines (theoretically 625/2, but you can choose to use 312 or 313).
Many computers/consoles use a fixed value of 312, Amiga can use both.

At this point if you want to have perfectly square pixels in 4:3 you need to use a horizontal amount of pixels equal to 384.

This is why some old digital professional devices store square pixels with a frequency of 14.75MHz (768x576pixels), which corresponds to 7.375MHZ per pixel in low resolution (384x288).

BUT

From here you can immediately understand that with the basic Amiga frequency it is not possible to have such a horizontal resolution...
Anyway you can easily calculate how many max pixels you can have, no more square.. (and actually see them on screen on some monitors):
Amiga PAL base frequency is 7093790Hz, Denise can emit pixel for ~53us on a line of 64us (a little more that the default value of 52us, so on some device a few may not be displayed) = 376 lowres pixels.

So max overscan is 376x286 (yes, two lines, the first and the last are unusable).

[technicality: usable lines range from $1a to $137 inclusive ($138 on some early Amiga 1000)
$19 is the line where sprites POS/CTL are fetched, $138 can use only background color]

Last edited by ross; 02 July 2019 at 21:38. Reason: sprites POS/CTL
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Old 02 July 2019, 20:31   #5
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Thanks. I saw in the WinUAE code also the max lines is 286. This helped a lot. I made an improvement to UAE4all2 Vita/Switch to allow up to 286 lines (was 270 before). Babeanoid seems to use almost all of them, it uses 280 lines!!! Quite impressive for an AMOS game, I'd say. Also it is a really cool game.
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Old 02 July 2019, 21:59   #6
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Babeanoid seems to use almost all of them, it uses 280 lines!!! Quite impressive for an AMOS game, I'd say. Also it is a really cool game.
I didn't know Babeanoid, and yes, a nice Arkanoid clone
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