Wikipedia:Reference desk/Archives/Computing/2020 May 18

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May 18

GNU emacs isearch whitespace mystery

Suppose I have a text file containing lines like this:

    <widget>
        <property name="title">
            <string>Hello, world!</string>
        </property>
    </widget>

Obviously this is XML (specifically a Qt ui file). I want you to imagine that the indentation is being done with ordinary spaces, specifically 8, 12, and 16 spaces for the lines shown.

The question has to do with finding the closing </widget> tag, which can get hard if there are dozens of enclosed elements. I know emacs has at least one major mode for XML, and there's certainly a handy command somewhere for finding matching tags, but I've never learned what it is. (And, please, let's not get sidetracked by that question; that's not the question here.)

What I'll normally do is type control-S, control-J, eight space characters, a '<' character, and if necessary a '/' and a 'w'. That should skip over every line that's indented by more than 8 spaces, and find the first line that's indented by exactly 8 spaces. And indeed that used to work fine.

Recently an OS upgrade got me to emacs 26.1, however, and something has changed. Now, when I try the search, it finds the first line that's indented by any number of spaces, not exactly 8 spaces. I suspect there's some new "convenient" mode where a space in a search automagically matches any number of spaces. But if so, this is puzzling and annoying, because the buffer in question is in Fundamental mode, which I thought should disable all such "conveniences".

Does anyone know what this mode is, and how to turn it off? Or, if my speculation about such a mode is incorrect, does anyone know why else my searches as described are failing? —Steve Summit (talk) 15:29, 18 May 2020 (UTC)

In the help for isearch-forward, I find the following:

Type M-s SPC to toggle whitespace matching.
In incremental searches, a space or spaces normally matches any whitespace
defined by the variable ‘search-whitespace-regexp’; see also the variables
‘isearch-lax-whitespace’ and ‘isearch-regexp-lax-whitespace’.

You may want to try setting search-whitespace-regexp to 'nil'. --Wrongfilter (talk) 15:42, 18 May 2020 (UTC)

@Wrongfilter: Thank you! Setting isearch-lax-whitespace to nil did the trick. (Thanks, too, for tolerating my laziness. I should have known that a trawl through the help screens would eventually limn the new feature, but frankly, I didn't have the energy today.) —Steve Summit (talk) 16:25, 18 May 2020 (UTC)

Four HD 1920x1080 screens from four computers on the same 3840x2160 4K screen.

I am looking for a large 4K monitor with four screen split (sometimes called picture-by-picture -- not to be confused with picture in picture). Here is an example of what I am talking about:

• https://www.lg.com/us/monitors/lg-43un700-b-4k-uhd-led-monitor
• https://www.lg.com/us/images/monitors/md07000640/gallery/zoom-01.jpg

That's four HD 1920x1080 screens from four computers on the same 3840x2160 4K screen.

My problem is that the LG linked to above has four HDMI inputs and my four computers all have DisplayPort outputs. I can try using four DisplayPort to HDMI Adapters[1], but what I would really like is a monitor with four DisplayPort inputs. Does such a monitor exist? Bigger is better, otherwise the 1920x1080 screens will be really hard to read. This will be installed on a factory floor, so any physical size will fit. --Guy Macon (talk) 15:35, 18 May 2020 (UTC)

The term of art for this is "quad view". I don't think you'll find quad view on consumer TVs, as it's not something consumers care about. You can get it on broadcast studio TVs (where a TV director has to look at multiple feeds), but these tend to be quite small (because the director is right in front of them) and, as professional equipment, they're very expensive (like $1500). You can get external tiler equipment quite cheaply (say $140) that tiles 4 HDMI feeds into one - but beware the max resolution. The consumer grades will mostly only output 1080p (so effectively you're getting 4x540p). If you're just intending to use the 4 computers as dynamic signage or cctv, that might be enough for your purposes. But if you need 4k out, conserving the 1080 from each display, again you'll probably need a piece of professional equipment. Companies like BlackBox make 4k in 4k out 4-pane multiviewer boxes (they're intended for higher end conference and education room applications) and again you're looking at $1500 or more. Given how cheap consumer TVs are these days, if cost is an issue then you're probably cheapest just buying 4 TVs. 87.112.77.203 (talk) 21:03, 18 May 2020 (UTC)

A TV and a computer monitor are similar (both typically accept HDMI inputs from a computer or a DVD player, for example) but typically have different features. I am looking for a computer monitor, not a TV. Security camera monitors (and their close cousins, car backup camera monitors0 typically accept BNC inputs. The security world calls four images on one screen "quad view" but as far as I can tell no computer monitor maker calls it that.

Saying I won't be able to find the feature right after I posted a link to a 43" computer monitor that has it[2] is less than helpful. --Guy Macon (talk) 02:51, 20 May 2020 (UTC)