[PATCH 00/15] weston scaling support

[John Kåre Alsaker]

On Tue, Jun 4, 2013 at 10:24 PM, Bill Spitzak <spitzak at gmail.com> wrote:

> John Kåre Alsaker wrote:
>
>      And I'm worried that high-resolution pointing devices will be
>>     ignored by clients that immediately round to the nearest buffer pixel.
>>
>> Presumably they wouldn't use the high-resolution for anything then. I'm
>> not sure how this relates to the topic either.
>>
>
> A client has to round event if it wants to do high-resolution, because it
> wants to align positions with things in the buffer. This gets pretty
> important with 3D modelling, lots of users and software assume that the
> mouse will stop on exactly the same fractional positions, and under your
> proposal this would change.
>
> For instance if there is a low-res device and a scale-3 output, then a
> client doing a hi-res display will get mouse positions of 1, 1.333..,
> 1.666..., in that window. If there is no low-res device and the hi-res one
> now has a scale of 1, then the client will get positions of 3,4,5.
>
> Multiplying the 24.3 fixed-point representation of 1.333.. by 3 gets
> 3.996. The client has to round this to 4 or it will align things slightly
> different on one system than the other. I can assure you that this
> difference is very annoying in 3D software.
>
> The only solution is to figure out the resolution of the pointing device,
> transform the fixed-point event positions to the buffer positions, and then
> round to the nearest multiple of the pointing device resolution. I think a
> lot of software will ignore the "figure out the resolution of the pointing
> device" step and just assume it is 1 pixel. Therefore any possible
> high-resolution pointing will be thrown away.
>
> Getting the events in buffer pixels would make it a lot easier as they
> could be used unchanged. Clients could then just assume any fraction is due
> to a high-resolution pointing device.
>
This is still a problem without any high-DPI stuff. You could just as
easily have an input device with a resolution 3 times higher than the
display.
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