[patch] prevent zoom level from jumping after click on slider

[Adrian]

What steps will reproduce the problem?

1. Load some OSM data
2. Zoom out by a factor of 8 or more using the scroll wheel. Note that the zoom slider does not move.
3. Drag the zoom slider

What is the expected result?

The zoom level changes one step at a time

What happens instead?

The zoom jumps back to where it was before step 2

Please provide any additional information below. Attach a screenshot if possible.

This is a regression since (probably) r11826 or r12039. The zoom slider used to move when zooming with the scroll wheel.

URL:http://josm.openstreetmap.de/svn/trunk
Repository:UUID: 0c6e7542-c601-0410-84e7-c038aed88b3b
Last:Changed Date: 2017-07-03 00:44:07 +0200 (Mon, 03 Jul 2017)
Build-Date:2017-07-02 23:26:36
Revision:12450
Relative:URL: ^/trunk

Identification: JOSM/1.5 (12450 en) Mac OS X 10.11.6
OS Build number: Mac OS X 10.11.6 (15G1510)
Memory Usage: 597 MB / 3641 MB (245 MB allocated, but free)
Java version: 1.8.0_131-b11, Oracle Corporation, Java HotSpot(TM) 64-Bit Server VM
Screen: Display 69680256 1366x768
Maximum Screen Size: 1366x768

Plugins:
+ ImportImagePlugin (33372)
+ InfoMode (33004)
+ PicLayer (33385)
+ apache-commons (32994)
+ cadastre-fr (33392)
+ download_along (32946)
+ editgpx (33004)
+ ejml (32680)
+ geotools (33380)
+ imagery_offset_db (33316)
+ jts (32699)
+ log4j (32699)
+ measurement (33088)
+ opendata (33358)
+ poly (33004)
+ reverter (33088)
+ turnrestrictions (33088)
+ undelete (33374)
+ utilsplugin2 (33328)
+ waydownloader (33167)

[Adrian]

The same problem arises after using the various View > Zoom to... functions (shortcuts 1 to 6, 8 and 9).

[Adrian]

This was broken by r12072. I spent many hours trying to understand what was going on, before I stumbled upon r12072. Patch attached.

Adrian

[Don-vip]

In 13201/josm:

fix #15039 - prevent zoom level from jumping after click on slider (patch by ar2988-os)

[Don-vip]

thanks for the patch! :)