<AWT Dev> RFR: 8257414: Drag n Drop target area is wrong on high DPI systems [v3]

[Olga Mikhaltsova]

> Please, review this small fix for drag-n-drop on Linux with HiDPI turned on!
> 
> This bug is due to the following reason: while scaling Java recalculates resolution (W x H) according to sun.java2d.uiScale (W/SCALE x H/SCALE) and works inside these new coordinates but at the same time the events, that come from the system, continue reporting positions in the old coordinates (W x H).
> 
> The idea of the suggested fix is in division of coordinates on the scale when they come from the system to Java and multiplying them on the scale when they go back from Java to the system. It is similar to processing events from mouse and buttons. 
> 
> Testing is quite complicated because for reproducing this bug the following conditions should be met:
> 1.	HiDPI is turned on
> 2.	sun.java2d.uiScale.enabled = true and sun.java2d.uiScale != 100%
> 3.	the source of drag-n-drop is non-java application
> 
> The step-by-step guide how to reproduce this bug is added to https://bugs.openjdk.java.net/browse/JDK-8257414.

Olga Mikhaltsova has updated the pull request incrementally with one additional commit since the last revision:

  8257414: Drag n Drop target area is wrong on high DPI systems

-------------

Changes:
  - all: https://git.openjdk.java.net/jdk/pull/1907/files
  - new: https://git.openjdk.java.net/jdk/pull/1907/files/e4c1c73d..d8259bdf

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=1907&range=02
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=1907&range=01-02

  Stats: 32 lines in 1 file changed: 2 ins; 17 del; 13 mod
  Patch: https://git.openjdk.java.net/jdk/pull/1907.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/1907/head:pull/1907

PR: https://git.openjdk.java.net/jdk/pull/1907