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First post, by PlaneVuki

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Hi.

Few questions about dosbox and cga after reading this: https://www.dosbox.com/wiki/Configuration:DOSBox

1. when setting machine to cga, does it emulate cga as it would look on rgbi monitor or composite monitor? Is there a way to fix the output to only one?

2. when machine is set to cga, scaler doesn't seem to work? What's the problem? (if there is a problem)

3. when machine is set to cga, it seems to work slower, there seems to be a lag when text scrolling and etc. What is happening?

Thanks in advance.

Last edited by PlaneVuki on 2022-03-15, 10:06. Edited 1 time in total.

Reply 2 of 11, by Jo22

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Hi there! 🙂

Yes, should be moved into DOSBox forum.
But I'm just an user, too. 😅

Here's what comes to my mind right now.
I'm speaking under correction. Might be wrong, thus.

1) DOSBox does try to detect the best mode for output.
Normal CGA modes are displayed as RGBI (with all palettes).
Composite CGA "modes" are displayed as Composite CGA.

2) The resolution can different to VGA emulation sometimes.
VGA emulation either uses 320x200 (4col CGA) or 640x200 (CGA hires in mono).
So it will use 200/400 line modes which are always line-doubled to 400 lines on a real VGA.

However, CGA emulation also supports these awkward CGA modes that are based on a hacked text-mode
These might be not line-doubled thus.

The DOSBox scaler normally only doubles resolutions like 320x200, unles forced.
So it might fail in certain native CGA modes.

"Time, it seems, doesn't flow. For some it's fast, for some it's slow.
In what to one race is no time at all, another race can rise and fall..." - The Minstrel

//My video channel//

Reply 5 of 11, by _Rob

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As mentioned, with "machine=cga", DOSBox defaults to RGBI, unless it detects that a game is trying to use artefact graphics in which case it will switch to CGA composite.

There are some key combinations that allow you to change some settings, once the game is started.

F12 = cycle between Auto, Composite and RGBI output modes.
F11 = decrease Hue
Alt-F11 = increase Hue
Ctrl-Alt-F11 = cycle between early or late IBM CGA composite emulation (conflicts with the key combination of switching to a TTY on Linux)

The DOSBox-X fork has some additional machine types to force RGBI or composite mode directly (but note that the above default key combinations have changed).

Reply 7 of 11, by zyga64

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Re: CGA Composite Mode under DOSBOX (Commited r3804)

1) VLSI SCAMP /286@20 /4MB /CL-GD5422 /CMI8330
2) i420EX /486DX33 /16MB /TGUI9440 /YMF718+GUS
3) i440BX /P!!!750 /256MB /MX440 /SBLive!+Vibra16s

Reply 8 of 11, by _Rob

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I tried it with dosbox-svn (development build), but I'm fairly sure it should also work with the standard dosbox 0.74-3.

Did you use "machine=cga"? Because it will not work otherwise. You also want to do it after you start the game.

There is no on-screen indicator when you press F12, and depending on the game there may not be a lot of difference. One way to know if the key presses are doing something, is to start dosbox from a windows command prompt. This way there will be some debug output on the console when you press the keys.

Reply 9 of 11, by PlaneVuki

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Rob, yes, I set machine=cga.
F12 works for me with one of the executables on r3804 commit page. But not on plain 0.74-3. Can you please check 0.74-3 and verify that it works? I would prefer to use a stable mainstream version rather than pick one of many other builds.

Reply 10 of 11, by _Rob

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@PlaneVuki, I am not one of the dosbox developers and will not test this for you on plain 0.74-3. You are free to use a SVN build or one of the forks or not, it's your choice.