(v13) The showpage operator

This page applies to Harlequin v13.1r0 and later; and to Harlequin Core but not Harlequin MultiRIP.

While a job is executing, it usually calls the showpage operator (or very rarely the copypage operator) from time to time. showpage is the operator which initiates the rendering phase. (If the system parameter AutoShowpage is true, then the RIP automatically inserts a showpage at the end of a job if there is not one there already and the job has made marks on the page.) This simple action sets in train a complex sequence of events as follows.

• The page device EndPage procedure is executed.

This can be set up to do a wide variety of tasks, but it must leave a Boolean on the operand stack. If this is true the RIP proceeds to render the page; if not, the showpage is effectively cancelled and only the BeginPage procedure is then executed (see below) before the action of showpage is complete.

The default EndPage procedure simply returns true under these circumstances.

• Rendering begins.

The StartRender procedures from the page device, if any, are executed. See (v13) StartRender procedures.

%pagebuffer% device parameters, which can vary from page to page or differ for each separation, are delivered to the device using the setdevparams operator. PageBufferSetup from the page device is called.

A file is then opened on the %pagebuffer% device.

The rendering sequence is repeated for each separation (or group of separations positioned together) demanded by the page device.

• The page is delivered to the %pagebuffer% device file.

The pagebuffer device type’s implementations for the setfileposition , writestring (and possibly readstring if a partial paint was carried out earlier see below) operators are called repeatedly to pass on the completed raster data. The data is produced in bands: equal size (except possibly the last) horizontal stripes across the page. Bands are usually issued in order the exception concerns parallel (SMP) implementations of the RIP. The format of the data how it is to be interpreted by the receiving device is given by a combination of the device parameters.

In the event of a non-fatal error, the sequence is repeated.

• The %pagebuffer% file is closed.
• The initgraphics and erasepage operators are executed. This is required by the semantics of the showpage operator.
• The BeginPage procedure of the page device is executed. The default BeginPage procedure simply discards its operands.

showpage is then complete and execution continues from the calling job.