[whatwg] Enabling LCD Text and antialiasing in canvas

[James Robinson]

Fonts are not vector art and are not rendered as paths at commonly read
sizes.  I don't think anyone is using or would be tempted to use LCD
subpixel AA for anything other than text.

- James


On Wed, Apr 3, 2013 at 5:07 PM, Gregg Tavares <gman at google.com> wrote:

> On Wed, Apr 3, 2013 at 5:04 PM, Rik Cabanier <cabanier at gmail.com> wrote:
>
> >
> >
> > On Wed, Apr 3, 2013 at 9:04 AM, Gregg Tavares <gman at google.com> wrote:
> >
> >> On Wed, Apr 3, 2013 at 8:41 AM, Stephen White <senorblanco at 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 at google.com>
> >> wrote:
> >> >
> >> >> On Sun, Mar 17, 2013 at 1:40 PM, Robert O'Callahan <
> >> robert at ocallahan.org
> >> >> >wrote:
> >> >>
> >> >> > On Sat, Mar 16, 2013 at 5:52 PM, Gregg Tavares <gman at 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]
> >> >> >
> >> >>
> >> >
> >> >
> >>
> >
> >
>