Re: [matplotlib-devel] Comparing pdf output in tests

[Andrew S. <str...@as...>]

Michael Droettboom wrote:
> Jouni K. Seppänen wrote:
>   
>> I am thinking about adding pdf comparison ability to compare_images. One
>> simple way to do this would be to convert pdf files to pngs using
>> Ghostscript: if we store reference pdf files, and both the reference
>> file and the result of the test are converted using with exactly the
>> same version of gs, there should be no font-rendering or antialiasing
>> mismatches.
>>
>> Can we assume that all test computers will have some version of
>> Ghostscript installed and callable as "gs"?
>>   
>>     
> We can probably standardize the version of gs on the buildbot machines, 
> but it's been very useful up to now to have tests that can run on a 
> variety of developer machines as well. 
>
> I don't know how different the output will be from different versions of 
> gs -- maybe we should just try it and see.  I have a pretty old version 
> of gs on my RHEL4 box (7.07).  If you want me to send you a png of a 
> particular pdf to directly compare with yours before you even start with 
> the test infrastructure, I'm happy to do that.
>   
I understood Jouni's idea to be to save the .pdfs as baseline images --
then the same version of gs would be used to generated the rasterized
images for the baseline and test result -- the version on your computer.
I think this is the way to go (either that or compare the PDFs directly
somehow).

Anyhow, allowing the test infrastructure to support testing multiple
backends is why I removed file extensions from the test image name in
the first place, so anything along these lines should hopefully be quite
doable. We could add a keyword arg to the image comparison decorator
that specified which image formats to test. Alternatively, it could
perform comparisons based on the presence baseline images of known
extensions.

-Andrew