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Atari demoscene BBS
| Re: About overscan/fullscreen |
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Posted by: evil
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Feb,09.2018-17:30
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There isn't a direct answer to this question as there are different methods to open the borders (left/right ones in particular).
Baseline:
Top border: Adds 29 scanlines
Bottom border: Adds 45 scanlines
Left border: Adds 48 pixels
Right border: Adds 48 pixels
SUM: 416*274
Double the width if in medium resolution.
But it is not that easy, there are some things that will reduce the number of pixels
1. Normally the first scanline is used for syncing the machine, reducing the line count to 273
2. ST machines (not STe) can start in four different states, each having slightly different lengths of the lines
3. The image is shifted four pixels left
4. At the end of each scanline there is something called stabilizer code (either a 71/50 Hz switch or MID/LOW switch)
After carefully using an OSSC to measure the output of my STfm and STe I came up with these dimensions of usable screen width:
<pre>
STfm WS1 total : 51+320+42=413 pixels
STfm WS2 total : 48+320+41=409 pixels
STfm WS3 total : 51+320+42=413 pixels
STfm WS4 total : 49+320+41=410 pixels
STe total : 51+320+40=411 pixels
</pre>
Then there is an STe-only overscan method that doesn't need the stabilizer code, most of our demos uses it as well as leonards. As it doesn't need any stabilizer and the STe doesn't have different wakestates.. It sure sounds like we would have a nice 416 pixels scanline! But no, this method shifts the screen 8 pixels to the right and we can actually see 49 pixels in the right border.
<pre>
STe total : 40+320+49=409 pixels
</pre>
For more details about my OSSC tests, here is what I found out:
http://ae.dhs.nu/hatari_overscan/
There are also illustrations how the image is shown in a full 512*313 window for the different wakestates and overscan methods.
--
Anders Eriksson
ae@dhs.nu
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