[cairo] CAIRO_DEBUG, take 2
ajohnson at redneon.com
Thu May 8 06:15:20 PDT 2008
Chris Wilson wrote:
> So far, through CAIRO_DEBUG, you can generate uncompressed pdf output,
> force the use of fallback images and fonts in the pdf/ps/svg backends
> and trigger a backtrace on a cairo_error(). (The backtrace now tries to
> use the better backtrace_symbols() from utils/backtrace-symbols.c.)
The ability to control PDF compression and enable/disable font
subsetters from an environment variable is something I've been wanting
to do for a long time. It is great to see the infrastructure coming
together so that it will be easy to these add options.
Quoting from README.debug:
> To enable the debugging output, one simply sets the CAIRO_DEBUG
> variable to the list of facilities desired.
> $ CAIRO_DEBUG=option1[,option2[,...]]; export CAIRO_DEBUG
> $ CAIRO_DEBUG=backtrace,abort; export CAIRO_DEBUG
> Alternatively, you can use any of " ,;:|" as the separator between
I think that allowing all these separators may create problems if in
future we want to have options that use various types of separators
within an option. For example "option=value1,value2",
"option_range=low:high" or "option_flags=foo|bar". I would prefer that
we choose only one separator. We can print a help message describing the
option syntax if there was an error parsing the options.
Carl mentioned on IRC is it would be useful to have "CAIRO_DEBUG=help"
print out a list of all the options so this would make it easy to find
out the correct use of the options.
For boolean options I prefer "option=true|false" (we could also accept
"0|1" and "t|f") instead of "disable-option", "enable-option", and
"force-option". It is less typing and allows an option in a script to be
toggled without needing the remove the option then remember what it is
called to put it back in again.
> force-fallbacks - Force the use of all fallbacks.
> force-fallbacks=image - Force the use of image fallbacks
> force-fallbacks=font - Force the use of font fallbacks
> force-fallbacks=image+font - Force the use of image and font fallbacks
> uncompressed - Prevent the pdf backend from compressing their
I would like to see more finer-grained control over the font subsetting
than this. For example a user may have a printer (or version of
ghostscript ) that has issues with TrueType fonts. It would be useful
to only disable the truetype subsetter for the PS backend without
affecting PDF fonts or PS Type 1 fonts. eg
Similarly with the compression it would be useful to set it per backend.
This would also be a good place to control the compression level as
originally proposed in . eg
to set the maximum zlib compression level on the PDF output. And
CAIRO_DEBUG=pdf.compression=0 or CAIRO_DEBUG=pdf.compression=false to
We could have "backend.option=value" to set an option on a backend and
"option=value" to set the same option on all backends. eg
"CAIRO_DEBUG=compression=0" to disable compression on all backends that
The option "force-fallbacks=image+font" isn't useful. If full page image
fallbacks are in use there will be no fonts to embed.
> [configure.in] Check release status (major.minor.micro)
> Define a CAIRO_RELEASE_STATUS in terms of micro/minor version and
> use it
> to set an enable debugging flag.
Not sure why this is useful. Isn't the point of the debug variable to
allow users using a release version to control options like the font
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