Screenshot size in vgaonly mode \ VOGONS

Screenshot size in vgaonly mode

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First post, by MrFlibble

Posted on 2014-02-19, 08:40

MrFlibble Offline

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I'm sorry if this has been asked (and dealt with before), but I searched the forums and haven't found anything that would address this particular issue.

Basically, when I run a game that has a 320x200 VGA mode with the default DOSBox settings and take screenshots, they retain the original dimensions (320x200). However if I switch to the vgaonly mode the screenshots are scaled up to 640x400. The scaler is set to normal2x in both cases. Is that the correct behaviour? If not, why does this happen?

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Reply 1 of 5, by h-a-l-9000

Posted on 2014-02-19, 19:13

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That's how it should be, because the real number of lines is still 400. The lines are put out twice each with identical data. Certain demo programs switch this duplication on and off to produce special effects. To support these, we need the high resolution.

1+1=10

Reply 2 of 5, by MrFlibble

Posted on 2014-02-20, 16:31

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Thanks for the explanation! I'm not sure I understood everything (I should look up some reference on how the real VGA mode works), but the fact that this is intended behaviour is enough for me. Thanks!

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Reply 3 of 5, by leileilol

Posted on 2014-02-21, 01:40

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VGA introduced doublescanned <350 height modes. Makes sense to me...

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Reply 4 of 5, by realnc

Posted on 2019-10-31, 00:06

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This is an old thread, but this recently came up in another place.

Why is this behavior only done with "vgaonly"? "svga_s3" for example does not do this. I thought SVGA is compatible with VGA so shouldn't it also do doublescan? Right now it doesn't. If the game runs at 320x200, you get an output of 320x200.

Reply 5 of 5, by xjas

Posted on 2019-10-31, 00:14

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AFAIK: VGAonly is scanline-level emulation to accommodate demoscene-style precision timing & beam racing effects. SVGA_S3 (etc.) emulate things at the video card firmware level.

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