[looping TUHS back in since I'm correcting a message I sent there] Hi Dave,
At 2025-05-06T08:36:55-0500, Dave Kemper wrote: > On Fri, May 2, 2025 at 7:35 PM G. Branden Robinson > <g.branden.robin...@gmail.com> wrote: > > I guess another way of saying this is that, as I conceive it, a line > > that is "adequately full" contributes to the page's uniformity of > > grayness by definition. > > For an example of less-than-ideal results if this is _not_ considered > the case (groff's behavior before this change), see > http://savannah.gnu.org/bugs/?60673#comment0 (the initial report that > precipitated the commit Doug is commenting on). Yes. In my reply to Doug I incorrectly characterized the resolution of this bug as a "2023" change of mine, but I actually landed the change in 2021. It simply took until 2023 to appear in a released _groff_. To make this message more TUHS-o-riffic, let's observe that input using DWB 3.3 troff and Heirloom Doctools troff (descended from Solaris troff, descended from DWB 2.0 troff [I think]), and both of which descend from Kernighan's device-independent troff circa 1980. $ DWBHOME=. ./bin/nroff groff-60673.roff | cat -s While the example in bug 57836's original report is somewhat contrived and a bit of an edge case in real life, there turns out to be a more innate bug in grotty's balancing algorithm. As mentioned before (and easily observable), when grotty adds spaces to a line in the process of justifying it, the algorithm it utilizes adds spaces from opposite ends of each line. But when it adds this space, it does not take into account lines with no adjustment at all required. Therefore if space only need be added to every other line of the text, all the space ends up being added to the same end of the line, degrading the uniform grayness of the output, as can be seen in this example. There is one fairly simple way to address this: grotty shouldn't "count" lines that don't need to be adjusted; instead, it should apply the alternation pattern only to those lines that do need adjustment. $ ./bin/nroff groff-60673.roff | cat -s While the example in bug 57836's original report is somewhat contrived and a bit of an edge case in real life, there turns out to be a more innate bug in grotty's balancing algorithm. As mentioned before (and easily observable), when grotty adds spaces to a line in the process of justifying it, the algorithm it utilizes adds spaces from opposite ends of each line. But when it adds this space, it does not take into account lines with no adjustment at all required. Therefore if space only need be added to every other line of the text, all the space ends up being added to the same end of the line, degrading the uniform grayness of the output, as can be seen in this example. There is one fairly simple way to address this: grotty shouldn't "count" lines that don't need to be adjusted; instead, it should apply the alternation pattern only to those lines that do need adjustment. They are the same, and differ from groff 1.22.4 and earlier only in that they adjust spaces starting from the right end of the line instead of the left. At the risk of tooting our own horn, here's how groff 1.23.0+ handles the same input. $ ~/groff-1.23.0/bin/nroff groff-60673.roff | cat -s While the example in bug 57836’s original report is somewhat contrived and a bit of an edge case in real life, there turns out to be a more innate bug in grotty’s balancing algorithm. As mentioned before (and easily observable), when grotty adds spaces to a line in the process of justifying it, the algorithm it utilizes adds spaces from opposite ends of each line. But when it adds this space, it does not take into account lines with no adjustment at all required. Therefore if space only need be added to every other line of the text, all the space ends up being added to the same end of the line, degrading the uniform grayness of the output, as can be seen in this example. There is one fairly simple way to address this: grotty shouldn’t "count" lines that don’t need to be adjusted; instead, it should apply the alternation pattern only to those lines that do need adjustment. Three observations: 1. One can find the input at Dave's URL above. 2. The input disables inter-sentence spacing. 3. The adjustment algorithm is a property not of grotty(1) (the output driver), but of GNU troff itself. Regards, Branden
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