[Patch] Fix icon rendering

[michael2402]

[10827] introduced a bug where the coordinates were not computed correctly.

I fixed the sign error and also made the selection box rotate with the image (it looked odd if the image is rotated and that box is not).

[Don-vip]

In 10842/josm:

fix #13375 - Fix icon rendering (patch by michael2402) - gsoc-core

[Klumbumbus]

Ticket #13377 has been marked as a duplicate of this ticket.

[Klumbumbus]

The rendering is a bit buggy. See the following screencast. First I zoom with the keyboard and then with the mouse. See how the icon jumps around in the red box. Also the text changes its position.

[Klumbumbus]

Another problem is that the icon box is unsharp. However I alreaedy noticed this before r10827 on high zoom levels. Now it seems it is always unsharp.

[Klumbumbus]

URL:http://josm.openstreetmap.de/svn/trunk
Repository:UUID: 0c6e7542-c601-0410-84e7-c038aed88b3b
Last:Changed Date: 2016-08-18 19:51:12 +0200 (Thu, 18 Aug 2016)
Build-Date:2016-08-18 17:56:08
Revision:10842
Relative:URL: ^/trunk

Identification: JOSM/1.5 (10842 de) Windows 7 32-Bit
Memory Usage: 384 MB / 742 MB (88 MB allocated, but free)
Java version: 1.8.0_101-b13, Oracle Corporation, Java HotSpot(TM) Client VM
VM arguments: [-Djava.security.manager, -Djava.security.policy=file:<java.home>\lib\security\javaws.policy, -DtrustProxy=true, -Djnlpx.home=<java.home>\bin, -Djnlpx.origFilenameArg=C:\Program Files\josm-latest-bla.jnlp, -Djnlpx.remove=false, -Djava.util.Arrays.useLegacyMergeSort=true, -Djnlpx.heapsize=256m,768m, -Djnlpx.splashport=63865, -Djnlpx.jvm=<java.home>\bin\javaw.exe, -Djnlpx.vmargs=LURqYXZhLnV0aWwuQXJyYXlzLnVzZUxlZ2FjeU1lcmdlU29ydD10cnVlAA==]
Dataset consistency test: No problems found
}}

[michael2402]

The problem is with how we define the center / position of objects.

The definition currently used is:

• Center is exactly the middle of the map view
• Objects are placed on the exact position, if they are between two pixel, antialiasing gives us that nice line

The jumping during zoom is caused by rounding problems: (int) rounds towards zero. Since some parts of the code are using translated coordinates, we may get differences there. After switching that to Math.round(), I still got flickering images. This was caused by the map view center not being aligned to a pixel (map view has an odd width/height).

I changed the zoom code to not use the exact center but a center close to the exact one. The component still aligns to the exact center. So if you move the window around, rounding errors caused by this will not sum up.

I attached the patch, it should fix the issue. I have not had time to test if it works in all zoom situations.

[Don-vip]

In 10856/josm:

fix #13375 - Fix icon rendering (patch by michael2402) - gsoc-core + add unit test