First post, by videogamer555
Here's a list of all the video modes that DOS is supposed to support (found on webpage http://stanislavs.org/helppc/int_10-0.html).
AL = 00 40x25 B/W text (CGA,EGA,MCGA,VGA)
= 01 40x25 16 color text (CGA,EGA,MCGA,VGA)
= 02 80x25 16 shades of gray text (CGA,EGA,MCGA,VGA)
= 03 80x25 16 color text (CGA,EGA,MCGA,VGA)
= 04 320x200 4 color graphics (CGA,EGA,MCGA,VGA)
= 05 320x200 4 color graphics (CGA,EGA,MCGA,VGA)
= 06 640x200 B/W graphics (CGA,EGA,MCGA,VGA)
= 07 80x25 Monochrome text (MDA,HERC,EGA,VGA)
= 08 160x200 16 color graphics (PCjr)
= 09 320x200 16 color graphics (PCjr)
= 0A 640x200 4 color graphics (PCjr)
= 0D 320x200 16 color graphics (EGA,VGA)
= 0E 640x200 16 color graphics (EGA,VGA)
= 0F 640x350 Monochrome graphics (EGA,VGA)
= 10 640x350 16 color graphics (EGA or VGA with 128K)
640x350 4 color graphics (64K EGA)
= 11 640x480 B/W graphics (MCGA,VGA)
= 12 640x480 16 color graphics (VGA)
= 13 320x200 256 color graphics (MCGA,VGA)
= 8x EGA, MCGA or VGA ignore bit 7, see below
= 9x EGA, MCGA or VGA ignore bit 7, see below
One of the first things I noticed when testing out these graphics modes (using some software I wrote myself using NASM assembler) is that mode 0E is not saving screencaps properly in DosBox. It is a 640x200 video mode. The real hardware monitor that receives the signal would be a specially designed monitor meant for this mode, and would have rectangular (not square) pixels and so would APPEAR to be displaying a 640x400 image, but the actual pixels are 640x200. DosBox's display mimics the appearance on a real monitor, and that's fine. However the screenshot you take with Ctrl+F5 is SUPPOSED TO save the actual pixels, meaning that it should be saving a 640x200 image. This will look distorted, but for accuracy of the image format, it should be saving the ACTUAL PIXELS. So imagine my dismay when I looked at the screencap it took and saw that it was a 640x400 image!
And that's not all. Mode 00 is supposed to be a text mode, just like Mode 01, except with black and white instead of 16 colors. But DosBox shows BOTH modes in color. Same thing with Mode 02 and 03. Mode 03 is supposed to be color, while Mode 02 is supposed to be 16 shades of gray grayscale. Again, DosBox makes the mistake of showing BOTH modes in color. There's several other problems like this in DosBox (one of them even has one of modes that is supposed to be a graphics mode, but DosBox is handling it as a text mode).
I highly encourage the developers of DosBox to go back over their code for emulating graphics modes, and use the list I've posted here as a reference for how the modes are SUPPOSED TO BE handled, and then correct any errors in their code for DosBox's display emulation, to make it so that from now on (whenever the next version of DosBox is released) DosBox will correctly render (and save screencaps from) each and every single one of these modes.