Re: Novel use of .char

[Deri]

On Wednesday, 18 December 2024 12:36:13 GMT Tadziu Hoffmann wrote:
> > I wrote "pdf: pdfpic" to mimic the behaviour of .PSPIC,
> > render image down from current point, [...]
> > The above difference means this works for pdf:-
> > 
> >   .char \[gnu] \v'-9p'\X'pdf: pdfpic GNU-head-small.pdf -L 10p'\h'10p'
> >   A GNU head \[gnu] image.
> 
> Thanks for the feedback!  This solution is perfectly workable.
> However, I had to change the -9p to -8.8p (which is the
> aspect ratio of the image times 10p) to get the baseline of
> the text to the right of the image to be aligned with the
> text on the left.
> 
> Interestingly, I also get a vertical shift if I wrap the sequence
> \v'...'\X'...' in \Z'...' which is supposed to restore the
> horizontal and vertical position after outputting the contents.
> Does that mean that the pdfpic special does not restore the
> graphics state (with q/Q) after inserting the image file?
> In that case there might be a discrepancy between what troff
> and gropdf consider to be the current output position.

Hi Tadziu,

Mea culpa (again!) although I was aware of this faux pas for a while. I 
mistakenly add the height of the image to gropdf's Y position after rendering 
the image. While this means that the sequence - up height of image : image : 
right width of image - as in Peter's code, works, it is clearly "wrong", as 
your \Z experiment shows. If I corrected this the sequence required would 
become - up height of image : image : down height of image : right width of 
image.

I have not done anything yet, (a) no one has reported it as bug, and (b) I 
hate changing existing behaviour which may affect users documents. Given what 
I discovered yesterday regarding grops rendering up from the base line and 
this aberrant behaviour of mine, I am gradually coming round to the view that 
a new "pdf: inline" (I did not like "pdf: pdfpicup", sounds like some sort of 
road vehicle!) is required, which would sit the image on the baseline as "ps: 
import" and leave the Y position well alone!! I would appreciate guidance on 
whether this is a good idea or not.

The reason why this behaviour has not been reported sooner is probably because 
.PDFPIC includes a break after the image so the grout file includes new H and 
V commands which reset the position for gropdf.

Cheers 

Deri