How to have ConTeXt ignore any `\externalfigure[]` code when a graphic is missing?

Question

I am using \externalfigure[filename.png] to display PNG files in my document in ConTeXt, e.g.:

\starttext
    \externalfigure[001.png]
\stoptext

Sometimes the file is not found. In this case, ConTeXt compiles, but displays a large gray space on the page where the image would be.

How can I get ConTeXt to print absolutely nothing there in the place where an image should be, in the event that the image file is missing?

Answer 1

I could not find an option for that, so the only alternative is to just delete the low-level command's body.

\unprotect
\def\grph_include_replacement#1#2#3{}
\protect

\starttext
\externalfigure[nop]
\stoptext

Output is empty page (as expected).

You can also use \doifelsefigure. The advantage over \doiffileexistselse is that this honours the resolver settings for images.

\setupexternalfigures[location={local,global,default}]
\starttext

\doifelsefigure{nop}{\externalfigure[nop]}{}

\stoptext

Answer 2

You could use the \doiffileexistselse command (or \doifelsefileexists which does exactly the same thing), which has the syntax

\doiffileexistselse{file name}{true code}{false code}

Thus your MWE becomes

\starttext

\doiffileexistselse {001.png} {\externalfigure[001.png]} {}

\stoptext

You could define a wrapper around it, for example I've defined a \tryexternalfigure command which seems to work alright. Then in the main text you can use it with the same syntax as \externalfigure, and it is smart enough to handle the 1 to 3 arguments \externalfigure expects.

\def \tryexternalfigure {\dotripleempty \dotryexternalfigure}
\def \dotryexternalfigure [#1][#2][#3]{%
  \iffirstargument
    \doiffileexistselse{#1} {\externalfigure[#1][#2][#3]} {}%
  \fi
}

\starttext

\tryexternalfigure[001.png]

\tryexternalfigure[002.png][scale=2000]

\stoptext