Improve state of the art for screenshot testing

[hmaarrfk]

port of pygfx/pygfx#827

[hmaarrfk]

hmm i guess i need to take WPGU_FORCE_OFFSCREEN a little further too.

[Korijn]

@hmaarrfk you want me to merge this or does it need some work?

[hmaarrfk]

i think this is fine as is right?

I'm not sure if the testing was improved since Aug 24, but i just wanted to keep them in sync. that is finding the "small difference" and the tuning parameters for the tolerance.

[hmaarrfk]

hmm i guess i need to take WPGU_FORCE_OFFSCREEN a little further too.

ohhh with this comment...

[hmaarrfk]

yeah give me som etime... you know... one day..

[hmaarrfk]

I think i remember my concern. there was an other very similar environment variable in this project, and I needed time to figure out the interaction (and I still need time to do so)

[hmaarrfk]

Ok at the time, I just had a hard time choosing a variable name.

I think I didn't want to propagate the documentation of 3 variables:

• WGPU_ADAPTER_NAME (which doesnt seem to work)
• PYGFX_WGPU_ADAPTER_NAME -- pygfx only
• WGPUPY_WGPU_ADAPTER_NAME wgpu, so I guess pygfx can use this (this is likely where I got stuck mentally)

Anyway, corrupting an example and running the new instructions in the readme yields:

[hmaarrfk]

needless to say, #659 needs to be resolved first

[Korijn]

LGTM. @almarklein I'll let you merge if you're okay too.