[jbosstools-issues] [JBoss JIRA] (ERT-755) Device#getDPI method can return incorrect values [EBZ#545953]

[Friendly Jira Robot (Jira)]

Friendly Jira Robot created ERT-755:
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             Summary: Device#getDPI method can return incorrect values [EBZ#545953]
                 Key: ERT-755
                 URL: https://issues.jboss.org/browse/ERT-755
             Project: Eclipse Release Train
          Issue Type: Task
          Components: Platform
            Reporter: Friendly Jira Robot


Since the fix for Bug 535064 there is an issue with Device#getDPI method that can under some unclear conditions return an incorrect DPI. Since my comment in the original bug went unnoticed I'm creating a new bug to raise this issue.

Here's my comment in the original bug:

I'm noticing a strange behavior of Device#getScreenDPI on my system (Ubuntu 18.04 with latest updates, and GTK version 3.22.30). The returned DPI value is {102, 102} instead of {96,96} as it should be. I've tried to debug the issue and here are the values used for DPI calculation:
widthMM=480,scaleFactor=1,monitorGeometry={0, 0, 1920, 1080}

This gives 254*1920/(480*10.0) = 101.6, value then rounded to 102.

I've tried to reproduce this issue with VirtualBox with a clean 18.04 install but couldn't. Although it's the same system, returned widthMM is different:

widthMM=503,scaleFactor=1,monitorGeometry={0, 0, 1920, 988}

Which gives 254*1920/(503*10.0) = 96.0, which is correct.

Is this a bug? Running $ xrandr --query gives
Screen 0: minimum 320 x 200, current 1920 x 1080, maximum 8192 x 8192
VGA-1 connected primary 1920x1080+0+0 (normal left inverted right x axis y axis) 480mm x 270mm

So the 480mm value is there, but I am not sure what this means. The result is that Eclipse 4.9 and onward return and incorrect DPI value on my system.

"xrdb -query | grep dpi" gives the correct DPI as follows:
Xft.dpi:	96



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