[wayland HiDPI support, posible regression?]

[Jason Ekstrand]

On Tue, Mar 10, 2015 at 12:00 PM, Bill Spitzak <spitzak at gmail.com> wrote:
> On 03/09/2015 10:32 PM, Jasper St. Pierre wrote:
>>
>> Mouse input is reported in a 24.8 fixed-point format. Subpixel mouse
>> locations are entirely possible.
>
>
> Yes events are doing this which is ok.
>
> There is a problem that clients must round to the correct pixel. If the
> rounding done by the client does not match the rounding used by the
> compositor to position the mouse cursor there may be annoying misalignment
> of the graphics. However this problem exists for high-precision mice
> irregardless of high dpi settings, so it is probably best to just document
> the rounding that must be used to position cursors: to convert a 24.8 mouse
> position to a pixel use (x*scale+127)>>8, the offset must be 127 (not 0 or
> 128) and you must use right shift, not divide by 256 (because that will
> shift negative values in the wrong direction).
>
> Events seem to be ok, but my complaint is that a large number of coordinates
> in the api other than events are in integer logical pixels, not in high dpi
> or in fixed-point. The offsets to attach are the biggest culprits. There are
> also integer clip rectangles in the subsurface and scaling apis. Except for
> compatibility there is no reason positions in messages cannot be in buffer
> pixels.

Please do not take a thread started by someone who is obviously
confused and side-track it into a discussion of things that you think
are design-flaws in the current protocol.  This is not the appropriate
place for a discussion of wl_surface.attach (x, y) coordinate systems
and bringing that up only adds to the confusion.
--Jason

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