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Re: [tor-bugs] #16005 [Tor Browser]: webgl.min_capability_mode might be too minimal

#16005: webgl.min_capability_mode might be too minimal
-------------------------+-------------------------------------------------
     Reporter:           |      Owner:  mikeperry
  mikeperry              |     Status:  needs_review
         Type:  defect   |  Milestone:
     Priority:  normal   |    Version:
    Component:  Tor      |   Keywords:  tbb-fingerprinting, tbb-usability-
  Browser                |  website, ff38-esr, tbb-5.0a-highrisk,
   Resolution:           |  TorBrowserTeam201506R, MikePerry201506,
Actual Points:           |  GeorgKoppen201506R
       Points:           |  Parent ID:
-------------------------+-------------------------------------------------

Comment (by mikeperry):

 Replying to [comment:15 gk]:
 > After some back and forth it seems there are some issues with my old OS
 X system using the ESR 38 based Tor Browser. Might be a more general bug
 in our toolchain or something only happening locally. I'll file a ticket
 as soon as we have an alpha I can point to. On Windows 7 on a different
 computer it is working fine for me.
 >
 > The code looks good, I think, but I have two questions:
 >
 > 1) I am a bit worried about not disabling the highp precision. Are we
 sure that all GPUs support it? It seems to be optional:
 https://community.arm.com/groups/arm-mali-graphics/blog/2013/05/29
 /benchmarking-floating-point-precision-in-mobile-gpus (while this post is
 mobile specific it might apply to the desktop world as well).

 Unfortunately highp precision seems to be required for this game to avoid
 the flickering. On my mobile and desktop CPUs,
 https://www.browserleaks.com/webgl lists the "Best Float Precision" for
 both vertex and fragment shaders as [-2^27, 2^27] (23). I am not sure if
 this is a function of highp or not, though. The browserleaks result didn't
 seem to change for me when toggling the pref or with the patch. Does it
 for you?

 > 2) Could you add a comment explaining what these *ALIASED*RANGE things
 are for (given that these are not existing in vanilla code) and what |1,
 MINVALUE_GL_ALIASED_LINE_WIDTH_RANGE| and |1,
 MINVALUE_GL_ALIASED_POINT_SIZE_RANGE| mean in this context? One might
 think that they make values in these ranges (1-5 and 1-255) acceptable
 which might depend on user configuration/hardware which is not the case I
 guess. Having some explanatory remarks might help understanding this part.

 Ok, I will add some comments to this code before merging.

--
Ticket URL: <https://trac.torproject.org/projects/tor/ticket/16005#comment:17>
Tor Bug Tracker & Wiki <https://trac.torproject.org/>
The Tor Project: anonymity online
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