Thanks for your reply. On 13/08/2021, Theo de Raadt wrote: > The vga(4) manual page takes no position on these details.
This is true. That's why the man page is TECHNICALLY correct. However, as currently put, it is also sufficiently misleading to have convinced multiple readers and Wikipedia editors that a naive arithmetic of the 80x25 standard VGA text mode with its 8-bit wide character definitions should yield 640 horizontal pixels (but it doesn't, because of each character's mode-inserted ninth column). You're quite right, THEY'RE jumping to conclusions, and man 4 vga does not state what the screen's pixel resolution is. That said, the vga(4) man page gives the uninformed and unaware plenty of rope to hang themselves with. This is what I propose addressing, but since I don't understand all the listed modes particularly well, I'm asking for help. Instead of: "Characters are 8 x 16 pixels large, and a font consists of 256 characters", would it suffice to say: "8x16-font characters are rendered in 9x16-pixel cells, and a font consists of 256 characters"? Or alternatively (and with context) maybe this? "This is the standard VGA text mode with 80 columns and 25 rows. 16 different colors can be displayed at the same time. Characters are defined in 8 x 16 fonts, but rendered in 9 x 16px cells, with an standard VGA adapter-inserted ninth column, for a total screen resolution of 720 x 400px. A font consists of 256 characters." Too clumsy? Can anyone do better? There's also the issue that a (potentially misleading) character size description shows up four times on the man page (the other four modes that don't mention one are the corresponding -bf variants). But I'm not actually sure if those modes that are not the standard VGA text mode really use 9 or 8-pixel wide cells. I certainly would not want to change vga(4) from correct but misleading to wrong! It appears the misleading language is originally from NetBSD. It looks like an earlier version of the vga(4) man page was present in NetBSD 1.4 (released May 1999)[0], from whence it found its way to OpenBSD 2.9 (released June 2001)[1]. The odd 40- and 24-line modes were also added in NetBSD, sometime between 1.4 and 1.5. I'm still unclear on which of these non-standard modes are 720px and which are 640px wide. But since I couldn't figure out where to look for enlightenment from source code, I did some practical experiments. The results were interesting: First I did some pixel-counting on an old OpenBSD laptop, and it seemed there were only 8 columns per cell, so I wondered, am I taking crazy pills? Then I hooked that laptop up to an external VGA monitor that can tell you the resolution via an On-Screen Display. I am not taking crazy pills, but it seems proper VGA support is on the wane. * When that laptop first boots its BIOS, its text mode is actually not the standard VGA text mode, but an approximation using 8x19cells, and though the monitor identifies the mode as 640x480/60Hz, it's actually 640x475, as the 5 lines at the bottom remain black, and so you get some kind of 80x25 text mode. * As soon as OpenBSD's first-stage biosboot(8) has control, the laptop switches to the real standard VGA text mode, i.e. 720x400/70Hz with 9x16cell 80x25; the real McCoy, the whole nine yards, the complete enchilada. * Once wsdisplay0 loads, the mode changes again; probably to something hi-rez or other. The long and the short of it is that, yes, vga(4) DOES in fact default to the real standard VGA text mode that's been around for donkey's years. WITH nine-column character cells. WITH 720x400px. I noticed that while I could switch the display from the laptop's screen to external VGA, I could not mirror it until wsdisplay0 was up. That's normal. Far weirder though was that if I switched back to the built-in screen while at the boot> prompt, the laptop rendered the text in that weird 640x475 mode again. Change to the external monitor again, and its VGA output is the entirely default and correct 720x400 mode. Of course some laptop's quirks don't have too much to do with OpenBSD, but what has something to do with OpenBSD is understanding what resolution these eight vga(4) modes actually are. I'm certain about the default 80x25 mode now. I would need to look into wsconscfg(8) etc. to figure out the rest, but that's for another day; I've gone on long enough. But any input, any assistance to make this actually yield an improvement would be very welcome! In the end of the day, I don't want some Wikipeejit to blame OpenBSD for their mode-ical misinformation: "But they said...", yadda, yadda, yadda. Thanks and regards, Ian (Ian Ropers) [0] https://man.netbsd.org/NetBSD-1.4/vga.4 [1] https://man.openbsd.org/OpenBSD-2.9/vga.4 c.f. https://www.openbsd.org/plus29.html > ropers wrote: > >> Privyet, >> >> On man 4 vga, it says: >> >> "This is the standard VGA text mode with 80 columns and 25 rows. (...) >> Characters are 8 x 16 pixels large (...)." >> >> To my understanding, that is borderline technically correct, but >> misleading: >> >> A naïve calculation of the screen's pixel resolution from these data >> would yield 640x400px. However, AFAIK, the VGA adapter still treats >> text mode like the MDA adapter did[0], which means that though each >> character's matrix is an eight pixel-wide bitmap (sometimes only seven >> pixels are actually used), the adapter itself always renders a ninth >> pixel for each text mode character (and scanline). Usually that pixel >> is blank, but for characters C0h–DFh, it is a copy of what was in the >> eighth pixel. This special-casing of characters C0h through DFh >> (where horizontal box-drawing characters and the like are usually >> located) can be turned off in VGA adapters[1], but is hardwired into >> MDA cards. The long and short of it is that with a total of nine >> pixel-columns being rendered for each character-column, the >> pixel-resolution of the standard VGA text mode is 720x400, not >> 640x400, as some have naïvely calculated. >> >> Why am I making noise about this, when the description on vga(4) is >> TECHNICALLY correct? >> Because I have noticed that ever since this edit[2], OpenBSD has been >> cited at Wikipedia as evidence for the incorrect assertion that the >> default VGA text mode was 640x400px. Evidently the editor in question >> has made exactly the naïve (mis)calculation noted above. (By this >> edit[3], the error had been propagated to the article's main text >> modes table, leaving it further entrenched.) >> >> I don't intend to get involved in correcting this at Wikipedia (which >> would probably lead to a life force-sucking edit war), but it bothers >> me that OpenBSD's man page appears to be misleading on this point. >> Though the page actually cited is from OpenBSD 3.9, the same wording >> is still present in 6.9 and -current, with minor differences in >> formatting. >> >> >> ======================================================================== >> Would people here be able to confirm that I'm not myself mistaken in >> what I'm saying? And could anyone suggest how to word an edit so as >> to concisely clarify the point and make the vga(4) man page less >> misleading? I'm not always good at being concise myself. >> ======================================================================== >> >> >> * I think the 80x25 & 80x25bf, as well as the 80x50 & 80x50bf modes >> all are 720x400px. If the 80x25 mode in particular is not 720x400px, >> then it is not the standard VGA text mode (as is claimed). >> >> * The 80x40 & 80x40bf modes confuse me. It's unclear to me if they >> render a ninth pixel-column and thus whether their screen width is 640 >> or 720. Arithmetically, 8x10px characters with an 80x40 text mode >> ought to yield 640x400px, but the only information I could find is >> here[4], and it suggests a display resolution of 640x480, which is >> neither here nor there. It would make sense with two extra blank >> scanlines per line of text, but then again, 480 instead of 400 could >> be a typo. I'm also confused by these modes because I'm much more >> familiar with 80x43 text modes and I'm low-key wondering whether 40 >> instead of 43 is an error. This page[5] makes no mention of an 80x40 >> text mode. I realise that is an altogether different project, but >> still. >> Second thought, I did find this[6], which suggests an 8x12px font for >> an 80x40 text mode, but then, this is again an altogether different >> project and may be nothing to do with OpenBSD's 80x40 text modes. I'm >> just wondering how VGA-typical are those? >> >> * If the only difference of the 80x24 & 80x24bf modes from their >> 25-line counterparts is the omission of the last row of text, then >> maybe these are 720x384px? I really don't know though. >> >> * I think the "bf" in the *bf modes is for "big font" or "bigger >> font", but I could not find confirmation of that. Also, if I'm >> reading this right, then it says under BUGS that these modes have not >> been tested and won't work with a monochrome monitor. (It's a little >> unclear to me how that's meant.) >> >> >> I have tried looking at source code, but I don't really know where to >> look, and at least in /src/sys/dev/ic/vga.c, I've not been able to >> identify anything that specifies the correct size of the actual >> default 720x400 VGA text mode, or that would account for the 9th >> pixel-column in each character. I've not been able to use the source >> to answer my own questions. >> >> Any help or clarifications would be great appreciated. >> >> Thanks and regards, >> Ian >> >> (Ian Ropers) >> >> >> PS: Btw., can anyone elucidate the etymology of the "ic" in >> /src/sys/dev/ic/? Is it because these devices all have integrated >> circuits, or does the "ic" stand for something else? >> >> >> [0] http://www.seasip.info/VintagePC/mda.html#memmap >> >> [1] "LGA - Line Graphics Enable >> This field is used in 9 bit wide character modes to provide >> continuity >> for the horizontal line characters in the range C0h-DFh. If this >> field >> is set to 0, then the 9th column of these characters is replicated >> from >> the 8th column of the character. Otherwise, if it is set to 1 then >> the >> 9th column is set to the background like the rest of the >> characters." >> >> --http://www.osdever.net/FreeVGA/vga/attrreg.htm#10 >> >> [2] >> https://en.wikipedia.org/w/index.php?title=VGA_text_mode&diff=950771231&oldid=950759222 >> >> [3] >> https://en.wikipedia.org/w/index.php?title=VGA_text_mode&diff=1022622974&oldid=1021428913#PC_common_text_modes >> >> [4] https://opencores.org/projects/interface_vga80x40 >> >> [5] http://www.columbia.edu/~em36/wpdos/videomodes.txt >> >> [6] http://javiervalcarce.eu/html/vhdl-vga80x40-en.html >> >
