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# 4.12 Overlay and Continue Modes

A typical PostScript file has a beginning, a middle, and an end. The beginning defines certain features (e.g., macros, origin, orientation, scale, etc.) which will be needed to create the plot. The middle has the commands which actually do the plotting. The end tells the graphics device to put out the plot (`showpage` in PostScript) and reset the graphics state. Many of the illustrations in this cookbook are built up by appending PostScript files together. If you do this, the first file needs a ``beginning'' and no ``end'', the last an ``end'' but no ``beginning'', and the middle files need only a ``middle''. You accomplish this automatically with the Overlay (-O) and Continue (-K) options. Overlay indicates that this plot will be laid on top of an earlier one; therefore the ``beginning'' is not included in the output. The default is always no overlay, i.e. write out the ``beginning''. Continue indicates that another plot will follow this one later; therefore the ``end'' is not included in the output. The default is to output the ``end''. If you run only one plot program, ignore both the -O and -K options; they are only used when stacking plots.

Next: 4.13 Specifying pen attributes Up: 4. General features Previous: 4.11 Landscape and Portrait Contents Index