[PATCH 0/2] Support for high DPI outputs via scaling

[John Kåre Alsaker]

On Tue, May 14, 2013 at 9:46 PM, Bill Spitzak <spitzak at gmail.com> wrote:

>
>
> John Kåre Alsaker wrote:
>
>>
>>     I expect a compositor to render deviations of the desired scaling
>>     factor without scaling windows. The range when this is allowed is
>>     reported to clients so they can try to render at a size which will
>>     avoid scaling.
>>
>>     For example a compositor may want to use a 1-1.2 range with 1.1 as
>>     the desired scaling factor. A clients which are only able to draw at
>>     integer scaling factor would round that up to 2 and let the
>>     compositor downscale it. When the range for which compositor won't
>>     scale is send to clients we can avoid this.
>>
>
> I don't think a range is necessary. The client can just claim that it's
> window is scaled at 1.1 even though it drew it at 1. Or at 2.2 even though
> it drew it at 2. Nothing stops the client from doing this so you might as
> well make that the way integer scales are done.
>
Then the user drags the window that claims to be draw at 1.1 over to a
monitor with scaling factor 1. It will be downscaled even though it's a
perfect match for the monitor.


>
> With the range, what happens to a surface with a scale of 1.3? Is it
> scaled by 1.3? Or should it be 1.3/1.2 times larger than the one scaled at
> 1.2, which is actually 1.191666? For this reason I think any scale wanted
> by the client should be obeyed literally.

It will be scaled by client_scaling_factor/output_scaling_factor, which is
1.3/1.1.


>
>  We may also allow scaling factors below 1.
>>
>
> I think scaling factors less than 1 are going to be a requirement.
> Otherwise the "units" have to be for the lowest-resolution device, which
> seems silly if you have a huge hi-res screen and a small lcd low-res
> display on your keyboard.
>
Perhaps, but I'd expect clients to do a lot of rounded up making the
scaling not very linear.
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