[NTG-context] Disable reuse of figures

[Hans Hagen]

On 2/19/2022 7:30 AM, Aditya Mahajan via ntg-context wrote:
> Hi,
> 
> This is related to a bug report for the filter module:
> https://github.com/adityam/filter/issues/60
> 
> Normally, when the same figure is included twice, context only includes the figure once and refers to the included figure the second time. The option `object=no` to externalfigure is supposed to prevent that, but it doesn't work. For example, consider the following example the bug-report uses graphviz as the external program, but I have changed that to context to keep things self contained)
> 
> \usemodule[filter]
> 
> \defineexternalfilter
>    [graphviz]
>    [
>      filter=context --purge,
>      output=\externalfilterbasefile.pdf,
>      readcommand=\ReadPDF,
>    ]
> 
> \def\ReadPDF#1%
>      {\externalfigure[#1][object=no]}
> 
> \starttext
> 
>    Circle:
>    \startgraphviz
>      \startMPpage
>        draw fullcircle scaled 1cm;
>      \stopMPpage
>    \stopgraphviz
> 
>    Square:
>    \startgraphviz
>      \startMPpage
>        draw fullsquare scaled 1cm;
>      \stopMPpage
>    \stopgraphviz
> 
> \stoptext
> 
> Behind the scenes, the first \startgraphviz ... \stopgraphviz environment writes the content to an external file (\jobname-temp-graphviz.tmp), runs `context --purge \jobname-temp-graphviz.tmp`, which creates `\jobname-temp-graphviz.pdf`. The `\ReadPDF` macro then includees the file (with object=no).
> 
> At the next \startgraphviz .. \stopgraphviz, the same process is repeated. The `\jobname-temp-graphviz.pdf` file is overwritten and the new file should have been included. But it is not. The output contains the first image twice.
> 
> I thought that object=no should have prevented the reuse. In fact, if I compile the file with luatex, I get an error message:
> 
> ! error:  (pdf inclusion): file has changed '12-two-outputs-temp-graphviz.pdf'
> mtx-context     | fatal error: return code: 256
> 
> Any idea why object=no is not working?
the pdf file is kept open, for various reasons:

- performance
- the might be different pages to fetch
- analysis happens when the image is placed, inclusion happens later

so you try to reopen an already open file (which has not been completely 
processed)

Hans

-----------------------------------------------------------------
                                           Hans Hagen | PRAGMA ADE
               Ridderstraat 27 | 8061 GH Hasselt | The Netherlands
        tel: 038 477 53 69 | www.pragma-ade.nl | www.pragma-pod.nl
-----------------------------------------------------------------