W3C home > Mailing lists > Public > whatwg@whatwg.org > April 2013

Re: [whatwg] Enabling LCD Text and antialiasing in canvas

From: Gregg Tavares <gman@google.com>
Date: Wed, 3 Apr 2013 17:07:05 -0700
Message-ID: <CAKZ+BNpXH1G7gBmS=xEHtbmm56=KeRtn0tEw=MwVUfBqcs1-GA@mail.gmail.com>
To: Rik Cabanier <cabanier@gmail.com>
Cc: WHATWG <whatwg@lists.whatwg.org>, Stephen White <senorblanco@chromium.org>, Robert O'Callahan <robert@ocallahan.org>
On Wed, Apr 3, 2013 at 5:04 PM, Rik Cabanier <cabanier@gmail.com> wrote:

>
>
> On Wed, Apr 3, 2013 at 9:04 AM, Gregg Tavares <gman@google.com> wrote:
>
>> On Wed, Apr 3, 2013 at 8:41 AM, Stephen White <senorblanco@chromium.org
>> >wrote:
>>
>> > Would Mozilla (or other browser vendors) be interested in implementing
>> the
>> > hint as Gregg described above?
>> >
>> > If so, we could break out the LCD text issue from canvas opacity, and
>> > consider the latter on its own merits, since it has benefits apart from
>> LCD
>> > text (i.e., performance). Regarding that, if I'm reading correctly,
>> > Vladimir Vukicevic has expressed support on webkit-dev for the
>> > ctx.getContext('2d', { alpha: false }) proposal (basically, a syntactic
>> > rewrite of <canvas opaque>). Does this indeed have traction with other
>> > browser vendors?
>> >
>> > As for naming, I would prefer that it be something like
>> ctx.fontSmoothing
>> > or ctx.fontSmoothingHint, to align more closely with canvas's
>> > ctx.imageSmoothingEnabled and webkit's -webkit-font-smoothing CSS
>> property.
>> >  -webkit-font-smoothing has "none", "antialiased" and
>> > "subpixel-antialiased" as options. I think it's ok to explicitly call
>> out
>> > subpixel antialiasing, even if the platform (or UA) does not support it,
>> > especially if the attribute explicitly describes itself as a hint.
>> >
>>
>>
>> Why call it "Font" smoothing? Shouldn't a UA be able to also render paths
>> using the same hint?
>>
>
> I have not heard of anyone using sub-pixel antialiasing for vector art. It
> might look weird...
>

??? Fonts are vector art.  Why should this flag be specific to fonts?  So I
decide tomorrow that I want vector art to be prettier than the competition
in by implementing LCD anti-aliasing I'll have to lobby for a new flag to
turn it on? Why?




>
>
>>
>>
>> >
>> > Stephen
>> >
>> >
>> > On Sun, Mar 17, 2013 at 11:17 PM, Gregg Tavares <gman@google.com>
>> wrote:
>> >
>> >> On Sun, Mar 17, 2013 at 1:40 PM, Robert O'Callahan <
>> robert@ocallahan.org
>> >> >wrote:
>> >>
>> >> > On Sat, Mar 16, 2013 at 5:52 PM, Gregg Tavares <gman@google.com>
>> wrote:
>> >> >
>> >> >> Let me ask again in a different way ;-)  Specifically about LCD
>> style
>> >> >> antialiasing.
>> >> >>
>> >> >> What about a context attribute "antialiasRenderingQualityHint" for
>> now
>> >> >> with
>> >> >> 2 settings "default" and "displayDependent"
>> >> >>
>> >> >>    context.antialiasRenderingQualityHint = "displayDependent"
>> >> >>
>> >> >
>> >> > How would this interact with canvas opacity? E.g. if the author uses
>> >> > displayDependent and then draws text over transparent pixels in the
>> >> canvas,
>> >> > what is the UA supposed to do?
>> >> >
>> >>
>> >> Whatever the UA wants. It's a hint. From my POV, since the spec doesn't
>> >> say
>> >> anything about anti-aliasing then it really doesn't matter.
>> >>
>> >> My preference, if I was programming a UA, would be if the user sets
>> >> "displayDependent" and the UA is running on a lo-dpi machine I'd
>> >> unconditionally render LCD-AA with the assumption that the canvas is
>> >> composited on white. If they want some other color they'd fill the
>> canvas
>> >> with as solid color first. Personally I don't think that needs to be
>> >> specced, but it would be my suggestion. As I mentioned, even without
>> this
>> >> hint the spec doesn't prevent a UA from unconditionally using LCD-AA.
>> >>
>> >> Very few developers are going to run into issues. Most developers that
>> use
>> >> canvas aren't going to set the hint. Most developers that use canvas
>> dont'
>> >> make it transparent nor do they CSS rotate/scale them. For those few
>> >> developers that do happen to blend and/or rotate/scale AND set the hint
>> >> they'll get probably get some fringing but there (a) there was no
>> >> guarantee
>> >> they wouldn't already have that problem since as pointed out, the spec
>> >> doesn't specify AA nor what kind, and (b) if they care they'll either
>> stop
>> >> using the hint or they'll search for "why is my canvas fringy" and the
>> >> answer will pop up on stackoverlow and they can choose one of the
>> >> solutions.
>> >>
>> >>
>> >>
>> >> >
>> >> > Rob
>> >> > --
>> >> > Wrfhf pnyyrq gurz gbtrgure naq fnvq, “Lbh xabj gung gur ehyref bs gur
>> >> > Tragvyrf ybeq vg bire gurz, naq gurve uvtu bssvpvnyf rkrepvfr
>> nhgubevgl
>> >> > bire gurz. Abg fb jvgu lbh. Vafgrnq, jubrire jnagf gb orpbzr terng
>> nzbat
>> >> > lbh zhfg or lbhe freinag, naq jubrire jnagf gb or svefg zhfg or lbhe
>> >> fynir
>> >> > — whfg nf gur Fba bs Zna qvq abg pbzr gb or freirq, ohg gb freir,
>> naq gb
>> >> > tvir uvf yvsr nf n enafbz sbe znal.” [Znggurj 20:25-28]
>> >> >
>> >>
>> >
>> >
>>
>
>
Received on Thursday, 4 April 2013 00:07:33 UTC

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