Clip path ignored except by pdfwrite

The Generic Mapping Tools (GMT; gmt.soest.hawaii.edu) uses PostScript for plotting. For some contour labels and texts we set up clip paths based on bounding boxes around each text item to ensure that later plot items do not overwrite the labels. We then turn clipping off. However, we believe we have found a bug in gs affecting this situation.

The attached file both2.ps illustrates the problem. The top panel places two rectangular text boxes as clip paths and the bottom places two rounded rectangles as clip paths [we are not showing the texts in either case]. Both panels are then overwritten by a rectangular hachure image, and due to clipping the boxes should be visible in page white. Converting the PS file to PDF works: gs, Preview, Distiller, and PS printers all render the correct result. However, when we use gs to produce a raster file (JPG, TIFF, PNG, etc) or use gv (which presumably needs to produce a raster as well) the clipping is absent and no errors are reported. We thus suspect there is a bug in the function that rasterizes the PS.

My particular gs version is 9.10 installed from macports under OS X 10.9.2, but reports from Linux and Windows are similar. I have reduced the PS file down as much as I could to minimize unnecessary code.

Sincerely, Paul Wessel

From:	Paul Wessel
Subject:	Clip path ignored except by pdfwrite
Date:	Tue, 6 May 2014 17:31:24 -1000