[wayland HiDPI support, posible regression?]

[microcai]

在 2015年3月9日 Monday 08:59:35，您写道：
> 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.

So mouse input is reported in logical pixels, and the logical pixels is not 
floating point numbers, resulting lost information when the surface are on 
hidpi display.

> 
> 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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