Wikipedia:Reference desk/Archives/Computing/2017 December 3#Another level of 3D experience

Why is the RGB colour #00000080 interpreted as black at exactly 0.5 opacity (at least by Firefox)? #…7f is treated as 0.498 ≈ {{frac|127|255}} and #…81 as 0.506 ≈ {{frac|129|255}}, for what it's worth. Jc86035 (talk) (notify me) 14:01, 3 December 2017 (UTC)

:The answer is "it shouldn't be" - 0x80 should be 0.502 ({{frac|128|255}}). [https://drafts.csswg.org/css-color-3/#rgba-color This] is the official W3C specification, linked from [https://developer.mozilla.org/en-US/docs/Web/CSS/color_value this] page on the Mozilla site, and neither say anything about a special case for 0x80. See also RGBA color space. Perhaps a bug report to the Firefox developers is in order? Tevildo (talk) 20:18, 3 December 2017 (UTC)

:It's very likely that the implementation of Alpha compositing uses hardware-accelerated, low-bit-depth (e.g. 8 or 16 bits) math for intermediate results, which could yield all types of varieties of rounding or loss of precision. Here's some more on [https://wiki.mozilla.org/index.php?title=Gecko:Overview&mobileaction=toggle_view_desktop#Compositing layer compositing in Gecko], the engine used by Mozilla Firefox. Casually glancing at that system schematic diagram, I see about six zillion places where a minor math or rounding error might cause a small but non-zero error in the final pixel value.

:If I had a dollar for every time I've seen a professional image-software programmer make a single-bit- numerical error in a compositing- or color space conversion- operation that resulted in a user-visible effect, ...I'd have a lot of dollars. Attention, all programmers: today's a good day to review the mathematics in error analysis and error propagation!

:As Tevildo suggests, a bug-report is in order: [https://bugzilla.mozilla.org/buglist.cgi?component=Graphics&product=Core&bug_status=__open__ it won't be the first] - accelerating the graphical operations in Gecko creates havoc ranging from minor glitches to catastrophic layout problems to [https://bugzilla.mozilla.org/show_bug.cgi?id=1419264 total machine-failures] - and those are just my cursory samplings of the bugs reported this week!

:Nimur (talk) 02:50, 4 December 2017 (UTC)

(I posted this question at the Entertainment RD, but I'll continue it here.)

Looking for a digital 3D CGI animation video format where I can hover the animating object over (similar to ZygoteBody, but I can freely move to any angle including top and bottom). It will be great if it does not rely on Adobe Flash. JSH-alive/^{talk/cont/mail} 16:31, 3 December 2017 (UTC)

:Preview / Mac OS provides this function with some file formats (eg .dae / Collada). The WP article lists a few more. --Cookatoo.ergo.ZooM (talk) 16:47, 4 December 2017 (UTC)

Can anyone recommend me a Windows equivalent or web browser-based ones? And it should have a time bar, so I'm able to skip forward or go back. JSH-alive/^{talk/cont/mail} 17:10, 6 December 2017 (UTC)