+#
+# -p uses PDF and the poppler library via pdftocairo for generating bitmaps,
+# simulating the output for Evince and other previewers using poppler.
+# pdftocairo may be contained in the poppler-utils package.
+#
+# -r can be used for specifying a rendering resolution. This
+# defaults to 101 for poppler and 300 for Ghostscript from PDF.
+#
+# -g uses Ghostscript for rendering a bitmap version from the PDF,
+# simulating the output from printing PDF files on a GNU system, so
+# use a resolution appropriate for print. Antialiasing is not enabled.
+#
+# -d changes the Ghostscript device used for creating PNG files
+# (usually png16m, but with -g you might prefer fewer colors for size
+# reasons, like png16).
+
+cpu_count=${CPU_COUNT:-1}
+backend_opt='--png ${resolution:+=-dresolution=$resolution} ${gsdevice:+=-dpixmap-format=$gsdevice}'
+resolution=
+gsdevice=
+
+png_generate()
+{
+ :
+}