The man page needs to explain what it needs to explain, and nothing more. What you are talking about below is beyond the scope of the page.
ropers <rop...@gmail.com> wrote: > 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 > >> > >
