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CGA Composite Mode under DOSBOX (Commited r3804)

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First post, by Jorpho

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Moderator note:
See the following post in this thread for info on recent composite CGA enhancements that have been committed to the DOSBox SVN: Re: CGA Composite Mode under DOSBOX
-- HunterZ

The Mobygames screenshots for Fooblitzky indicate that it can run in CGA Composite mode.

I notice that DOSBox 0.65 gives a little message about supporting Composite CGA if you change the machine type in dosbox.conf from VGA to CGA. However, even when running DOSBox in this mode, Fooblitzky comes up in black and white. The same thing happens in the CVS build.

Do I need to do something else to enable Compositie CGA, or is Fooblitzky doing something not supported by DOSBox?

Last edited by Jorpho on 2012-06-05, 16:44. Edited 2 times in total.

Reply 4 of 745, by Qbix

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well it's not very common, but it is possible. I would have to debug the game to see what it tries to set.

Water flows down the stream
How to ask questions the smart way!

Reply 6 of 745, by Great Hierophant

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Fooblitsky doesn't set anything special to enter composite color mode. If you connect it to a composite color monitor, you will see it in color. Othewise you will see it in 4-color CGA (even though the game only uses 2 colors.) DOSBox cannot handle this until it adds a composite CGA selection to the machine types. Actually, in my opinion, there should be a separate listing for monitor type, and support the following devices:

TTL Monochrome (for Hercules and EGA Mode 0Fh)
Composite Monochrome (for all 200 lines modes only)
VGA Monochrome (limited to 8-bit modes)
Composite Color (for all 200 line modes only)
RGB/VGA

Reply 8 of 745, by Harekiet

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If they want to output in composite they have to toggle a certain bit in the cga controller for the color burst. Dosbox detects that and switches to composite mode, seems to work for other composite mode games.

Reply 9 of 745, by Great Hierophant

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There are actually two graphic composite modes, DOSBox only implements the one Harekiet describes, which only works if the game is using a 640x200 resolution. The other composite mode uses the 320x200 resolution and is automatically selected if you the game uses Mode 4, whether the programmer intended it or not. If the game is using the cyan/magenta/white or red/green/brown palettes (and their intense versions), that game will display in color on a composite monitor. If the game uses Mode 5, with its cyan/red/white palette, the game will display in grayscale on a composite color monitor. The only difference in the CGA registers between Mode 4 and Mode 5 is that the color bit is set in the former and clear in the latter.

Reply 14 of 745, by Qbix

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perharps. but not for the next version, although that one will have a lot of new machine modes

Water flows down the stream
How to ask questions the smart way!

Reply 17 of 745, by KiyoteLockeWolf

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I might have solved this 4 year old (more?) problem.

I have a very old programming manual. It's been in my posession for years. It is really a xerox of a book, which was stapled together using carpet staples on the end.

From the previous posts, I gathered that setting CGA flags was correct.

On the very first page, (first one before got ripped off), it showed BASICA code to set the active graphics card between Monochrome Adaptor, and a CGA Adaptor in the computer at the same time.

I re-wrote the code in a QBasic wrapper, added my contact info as a 4 second msg, and compiled it into a single EXE. CMPOSITE.EXE

I tinkered with DOSBOX a bit, and it did indeed set the composite mode of the CGA (CGA video mode set of course) emulation.

Will it remain on in between various accesses of programs and other such processes? That depends.

I did a test of a CGA based Turbo Pascal program I wrote to see if the composite setting carried over. It did not. Maybe it's the way my program operates.

But, it did seem to work when running under BASICA at screen 1 & screen 2. (320x200x4) & (640x200x2) which are the composite modes of course.

This is obviously only a temporary fix, but MAYBE, it will work for your game(s).

I would love to see a list of which games this gets the composite flag working again on.

Love to chat about how I did composite CGA video graphics with my Tandy 1000HX, but I'm sure you guys wanna see the program I wrote.

Enjoy! Remember, this is only a homebrew patch that may or may not work.

BTW.. Try at your own risk. It only sets 2 low memory address values, so it won't even hurt a fly as far as I'm concerned.

Attachments

  • Filename
    CMPOSITE.EXE
    File size
    24.44 KiB
    Downloads
    883 downloads
    File comment
    Executable that may enable CGA Composite emulation for some DOSBOX games.
    File license
    Fair use/fair dealing exception

If it ain't borked, fix it 7 times.. Reinvent the wheel every day. Compile 8085/8086 code daily. Drink lots of instant coffee. Look both ways before cooking a turkey.

Reply 19 of 745, by KiyoteLockeWolf

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Since this is a luck of the draw, so to speak, I thought I'd show proof that my utility does do something to give some hope.

Here is a screenshot of Tandy EX Basic, running on a 640x200x2 screen, under composite emulation.

Upon running DOSBOX, I ran my utility, then the BASICA.EXE file.

GWBasic.EXE however, would not take this same method. It shows the composite screen for a second, then switches over to regular CGA with no colorburst.

I only have Dosbox .65 running on my computer right now, because I have bad drivers which crash .63 and .72 on me. I can't test this on other versions of DosBox right now.

Attachments

  • cgaproof.jpg
    Filename
    cgaproof.jpg
    File size
    27.52 KiB
    Views
    11904 views
    File comment
    CGA Composite emulation using CMPOSITE.EXE to enable it
    File license
    Fair use/fair dealing exception

If it ain't borked, fix it 7 times.. Reinvent the wheel every day. Compile 8085/8086 code daily. Drink lots of instant coffee. Look both ways before cooking a turkey.