[whatwg] Enabling LCD Text and antialiasing in canvas

[Rik Cabanier]

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...


>
>
> >
> > 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]
> >> >
> >>
> >
> >
>