[wayland HiDPI support, posible regression?]

[Jasper St. Pierre]

You misunderstood what pq said.

You work in "logical pixels". On a hi-DPI display, with twice the pixel
density, each "logical pixel" is backed by 4 device pixels. Your actual
backing surface containing the pixels is in "device pixels".

So, if you have an window that is 800x600 logical pixels, when you drag it
to a low-DPI display, your backing buffer is 800x600 device pixels. When
you drag it to a hi-DPI display, your backing buffer is 1600x1200 device
pixels.

When you submit your buffer, you tell the compositor what the ratio of
device pixels to logical pixels is, in the perhaps misnamed
"set_buffer_scale" request. So, for the low-DPI buffer, you submit "1",
since 800x600 / 800x600 = 1. When you submit your hi-DPI buffer, you submit
"2", since 1600x1200 / 800x600 = 2.

If you submit "1" and you are on a low-DPI display, it all matches and
things are fine. If you submit "1" and you are on a hi-DPI display, the
compositor scales up your buffer to match. If you submit "2" and you are on
a hi-DPI display, it all matches up and things are fine. If you submit "2"
and you are on a low-DPI display, the compositor scales down your buffer to
match.

On Mon, Mar 9, 2015 at 6:19 AM, microcai <microcai at fedoraproject.org> wrote:

> 在 2015年3月9日 Monday 10:39:20，您写道：
> > Hi,
> >
> > On Monday, March 9, 2015, microcai <microcai at fedoraproject.org> wrote:
> > > so we are forcing two code pathes in APP? or just support non-integer
> > > scale?
> >
> > Scaling is a specific fallback for legacy/non-DPI-aware clients, to get
> > them to show anything at all. Other clients will render at the
> appropriate
> > resolution already.
>
> That's not the story I was told. pg says scale is the *only way* to support
> HiDPI.
>
> >
> > Any plan that relies on integer scaling means you're wasting pixels on
> your
> > lovely dense display. Any plan that relies on non-integer scaling makes
> > your text blurry to the point of unreadable - again, a waste of pixels on
> > such lovely displays. Just render at the correct scale to begin with.
> >
> > Cheers,
> > Daniel
>
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>



-- 
  Jasper
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