[Matplotlib-devel] On testing with other FreeType versions

Sandro Tosi morph at debian.org
Mon Dec 11 12:30:08 EST 2017

Debian is also interested in this duscyssuib, we have a local patch to
increase the RMS of several tests, but i agree with Elliot the number
of failing tests is getting bigger and bigger and just bumping the
threshold is not always the best way (as we risk to make the testsuite
pass just to not feel bad, without actually spotting real issues).

I remember a similar conversation in the past, and the idea of
providing multiple sets of reference images, built with different
freetype versions, and to release them as an additional tarball the
downstream distribution can download and bundle up with the python
code release (remember debian dont want to download stuff during the
build, which is where we run the test suite).

i also like a lot Thomas' idea of having AI/ML actually inspect the
image and say if they are alike "enough" for the test to pass instead
of a pixel-by-pixel comparison, but it may be a long time effort (GSOC
maybe?) and we should also keep an eye on how long the test suite run
time it will be (mpl is already long enough to build as is lol)

On Mon, Dec 11, 2017 at 11:32 AM, Thomas Caswell <tcaswell at gmail.com> wrote:
> There may also be an interesting machine learning problem here to use a more
> intelligent criteria for determining if an image has failed.
> By changing the freetype version we have a bunch of images that do fail
> pixel comparison that should not and by slightly modifying tests or
> shuffling the test <-> result image  mapping we can generate as many do fail
> and should fail cases as we need.
> Tom
> On Mon, Dec 11, 2017 at 1:40 AM Antony Lee <antony.lee at berkeley.edu> wrote:
>> Hi,
>> 1. Sticking to testing with the old FreeType.
>> Injecting an older FreeType version is "relatively" easy to do (the
>> question is whether you want to do it...).  Naively, one could just set
>> LD_PRELOAD to /path/to/libfreetype.so, but that will also affect
>> subprocesses such as imagemagick, which (IIRC) don't like that, so instead
>> the correct way is to ensure that the Python process calls
>> `dlopen('/path/to/libfreetype.so', RTLD_GLOBAL)` which forces symbol
>> resolution *in this process* to first check the given path, but does not
>> affect subprocess (alternatively, one could remove LD_PRELOAD from the
>> environment before calling the subprocess but that seems messier).
>> Fortunately, dlopen is "effectively" available under the name of
>> `ctypes.CDLL` in Python.
>> I have a proof of principle somewhere that patches the testing framework
>> to 1) ensure that an old freetype is built (basically moving the
>> local_freetype implemenation from setupext to the main lib), and 2) loads it
>> as above.
>> Another relevant issue is the manylinux wheels, which must somehow embed a
>> libfreetype.  Currently I believe this is done via static linking.  This is
>> not so great if you also want to load freetype for other reasons; for
>> example mplcairo (which loads freetype via cairo) currently cannot work with
>> local_freetype builds due to symbol conflicts.  I believe that switching to
>> the standard manylinux approach (which is to include the shared object in a
>> hidden folder and set RPATH appropriately) would work better (and allow us
>> to strip out the static linking code).
>> 2. Switching to newer FreeTypes.
>> I don't think committing all test images to the main repo is really a
>> viable option: FreeType is also making new releases every once in a while
>> and different Linuxes have different versions
>> (https://pkgs.org/download/freetype gives 2.8.1 (Arch, Debian Sid), 2.8
>> (Fedora 27, Ubuntu 17.10), 2.6.3 (Debian 9, OpenSUSE 42.3), 2.6.1 (Ubuntu
>> 16.04 LTS) and that's only a few).
>> I do believe that adding tooling that generates the test images to a side
>> repo for each tag + FreeType version (say, using the FT versions of the
>> major distros at the time of the tag) may be reasonable.
>> 3. Side note.
>> If #9763 (or #5414) gets accepted (new FT wrappers), they will also
>> require a new generation of the test images: ft2font currently generates
>> "wiggly baselines" in certain cases (see example in #5414), and try as I
>> might (i.e. not so much) I could not reproduce them in the new wrapper :-)
>> Antony
>> 2017-12-10 21:44 GMT-08:00 Elliott Sales de Andrade
>> <quantum.analyst at gmail.com>:
>>> Hi all,
>>> Downstream in Fedora (and maybe Debian), they are running into issues
>>> with testing and text. Fedora 26 has FreeType 2.7.1 and Fedora 27 & Rawhide
>>> has FreeType 2.8. Fedora 25 uses 2.6.5, but it will be EOL in the next week.
>>> Many other distros are also transitioning to these newer FreeType as well
>>> [1] and I think anaconda recently added 2.8 too.
>>> With 2.7.1, a few tests fail (rms < 1) and it is straightforward to patch
>>> that [2]. With 2.8 though, over 800 tests fail [3] ranging up to ~80 rms
>>> [4]. This is a bit harder to paper over.
>>> I see a few ways to mitigate the problem, with varying
>>> advantages/disadvantages:
>>> 1. Bundle the older version in the Matplotlib package like we do with
>>> tests. I don't really believe this to be a viable option for downstream, but
>>> I'm just mentioning it to be thorough. There are already a few (minor)
>>> security issues in the one we test against.
>>> 2. Inject older FreeType just to run tests on the package. Again I don't
>>> like this idea. The point of running tests is to be sure that the version in
>>> a distro works *in that distro*. Testing with something a user could never
>>> install seems useless.
>>> 3. Re-create all our current and future test images with 2.8. While this
>>> is most future-proof, adding over 800 images is going to bloat the repo
>>> quite a bit.
>>> 4. Create some sort of side repo with test images for other FreeType
>>> releases. This would reduce bloat in the main repo but be somewhat more
>>> work. Thus I'd only suggest doing so for tags.
>>> I dislike the first two options as they would be repetitive across
>>> distros (unless they just stopped testing altogether), but the last two are
>>> not without work for us.
>>> Opinions? Alternative ideas?
>>> [1] https://repology.org/metapackage/freetype/versions
>>> [2]
>>> https://github.com/QuLogic/matplotlib/commit/cfdc835923407810bd087f60332cdc8cdcb23f05
>>> [3]
>>> https://kojipkgs.fedoraproject.org//work/tasks/3137/23623137/build.log
>>> [4] https://gist.github.com/QuLogic/477055a847a44cd444a0932432acffd1
>>> --
>>> Elliott
>>> _______________________________________________
>>> Matplotlib-devel mailing list
>>> Matplotlib-devel at python.org
>>> https://mail.python.org/mailman/listinfo/matplotlib-devel
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Sandro "morph" Tosi
My website: http://sandrotosi.me/
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