Bottom margin vs. descenders question

[Peter Flynn]

On 27/06/2020 10:37, Philip Taylor wrote:
> Peter Flynn wrote:
> 
>> I had to do it for display math once, so I invented an environment 
>> which set the equation, measured it, and output it vertically-centered 
>> in a vbox to an integer number of lines. Not elegant, but it helped.
> 
> I think you would agree, Peter, that if one is required to typeset on a 
> grid, then TeX's normal line-spacing ("leading") behaviour is useless 

Yes, once you leave the beaten track of type set solid, 
it's...umm...flexible, if I may put it politely :-)

But a very large amount of what I set is simply solid text, set to a 
depth which is an integral multiple of lines, with occasional section 
headings.

> With those parameters in effect, I have never found it possible to use a 
> \vbox with height an integral multiple of \baselineskip to achieve what 
> you were setting out to do, because said \vbox has only one reference 
> point. 

I think it only needed one. But it was some decades ago.

> This is why I formulated and proposed my \leaders solution.  
> Could I ask you to post a short fragment of code in which you 
> demonstrate how your idea would work, given the line-spacing parameters 
> above ?

I think yours is probably much more accurate. I don't think I have the 
code, but it was rough :-) Basically, set a displayed equation in a 
\vbox. Take the \ht and work out how many whole \baselineskips it needs. 
Set a \vbox to that height with the equation vertically-centred.

It was needed because the authors knew a lot about mathematics and as 
much about LaTeX as they needed to be dangerous. Because they didn't 
know how to lay out equations, they stuffed each one into a box and then 
used \scalebox to make it fit the page. The publisher thought it might 
"look wrong" but didn't know what to do with it, except that they could 
see that the line-alignment was going to be wrong on almost every page.

I can't remember what I charged, but it wasn't enough to do a decent 
job. Not a book we were proud of, alas.

Peter