[PATCH 00/15] weston scaling support

Bill Spitzak spitzak at gmail.com
Tue Jun 4 18:11:54 PDT 2013

John Kåre Alsaker wrote:

> 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.

I am worried that most clients will work around the problem of the scale 
proposal by rounding all numbers from 3.5 to 4.5 to 4, thus throwing 
away the high resolution input device.

Lets assume a screen has scale 3 and there is a pointing device with a 
resolution of 1/2 of these pixels. And the client is drawing a full-res 

(note the numbers here looks strange but they are the closest decimal to 
the 24.8 fixed-point values. That is why it is .332, not .333):

Under your proposal a normal pointing device will return 1, 1.332, 
1.664, 2, ... as coordinates. If the client just blindly multiplies by 3 
they will get 3, 3.996, 4.992, 6. I think most clients will fix this by 
rounding to the nearest integer to get 3, 4, 5, 6.

Now the high-resolution device will return 1, 1.164, 1.332, 1.5, 1.664, 
1.832, 2. If the client blindly multiplies these by 3 they will get 3, 
3.492, 3.996, 4.5, 4.992, 5.496, 6. However if the client rounds 
(possibly because the author never saw a high-resolution pointer) they 
will get 3, 3, 4, 4, 5, 5, 6, thus losing the high-resolution.

In my proposal a normal pointing device will return 3, 4, 5, 6. The 
client will not need to round. The high-resolution device will return 3, 
3.5, 4, 4.5, 5, 5.5, 6. Since the client does not round, it will get 
these values correctly.

Of course the client could only round numbers that are "close" to 
integers, but I still feel my solution is simpler.

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