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PostScript graphics files

In theory, any PostScript file can be incorporated into any other, so long as each obeys certain rules concerning what they are allowed to do to the `PostScript engine' producing the output. The full collection of these rules is called the `Adobe Document Structuring Conventions' (DSC) and while the phrase is widely-used, very little of this document is practically useful for day-to-day document preparation. The main points to note are:

Does the file to be incorporated have a %%BoundingBox: comment somewhere near the top? If not, then one must be calculated. If the file is printable by itself, then the simplest way to do this is to print it out, draw around the diagram the smallest rectangle which contains it, and convert the dimensions of this rectangle to `points'. For all practical purposes, there are 72 points to the inch, and 2.835 to the millimetre. Bear in mind that the printer's accuracy in grabbing a piece of paper from the feed tray is only around 1-2mm in any direction, and try not to become obsessed with accuracy.

All the utilities mentioned above can generate %%BoundingBox: comments in the right circumstances. However, PostScript appears on this site from all sorts of places, and it is wisest not to leave this to chance-check!

Diagram origin
Occasionally, utilities which generate PostScript do so in `egotistical' fashion, assuming that the user cannot possibly want anything else on the page with its graphics, and the output is rotated, scaled and centred on the page. This is all very well, but what is desirable for inclusion in is a diagram whose lower-left %%BoundingBox corner is at the PostSript origin. With most printers, this means that on printout of the file on its own, the lower left corner of the diagram will be `off the page' at the bottom left, because they are designed to believe that they are printing on an American 8.5''x11'' page, rather than European A4 (210x297mm).

Usually, persuading the file to produce its output at the origin involves finding the PostScript translate operator responsible and commenting it out. Then, it may be necessary to `translate' the %%BoundingBox comment to suit. xfig, xgraph and MacDraw can all be persuaded to produce `origin graphics'; xpr will need a little strategic commenting.

Graphics context
It is perfectly possible for a postScript graphic to leave the PostScript engine in a state in which it cannot continue, or to `mess about' with the state so that it is pointless to continue. The obvious example of this is the showpage operator. If the file has been produced with a view to printing it out alone, then somewhere at the tail of the file a showpage will appear, which to the PostScript engine means `this page description is complete; print it out'. In the case of a figure in a document, we would prefer the rest of the page, after the figure, to be added before that page is printed. Spurious showpages can be safely commented out.

Complications can also be caused by save/restore and gsave/grestore appearing in the included file. This is an area best avoided if possible, where, to use the time-honoured phrase, `experience and informed courage count for much'. Access to various PostScript manuals [Adobe85b][Adobe85a] is also useful here.

xfig, xgraph and idraw will produce showpageless code; xpr, again, may need some help.

Next: Incorporating the image Up: Generating graphics Previous: Generating graphics