[Interest] curve’s width in inch on different displays

[Rutledge Shawn]

On 23 Jan 2014, at 11:00 AM, Portale Alessandro wrote:

>> From: 梁伟钟 [lwz at xdt-inc.com]
>> Sent: Thursday, January 23, 2014 10:05
>> Subject: [Interest] curve’s width in inch on different displays
>> 
>> Hello,  I would like to set curve's width in inch and make sure it shows the same size on different 
>> displays with different resolutions.  How to do it ? Please help ,it's important. Thanks!
> 
> Qt reports a screen's dpi value:
>   http://qt-project.org/doc/qt-5/qscreen.html#logicalDotsPerInch-prop

http://qt-project.org/doc/qt-5/qscreen.html#physicalDotsPerInch-prop

The logical dots-per-inch value is more likely to be wrong, because of the convention of pretending that every HiDPI display is twice as dense as a regular-resolution monitor (on Mac OSX, these are set to 144 and 72 respectively, even though it's usually more in reality).

There are also displays that don't report correct values in the EDID info, which is where physicalDotsPerInch comes from on desktop platforms, assuming your operating system reads that info.  But it can usually be overridden in the OS (except on MacOS), so if Qt doesn't report correct values in physicalDotsPerInch it can be corrected.