Loading of http:// images blocks user input. It should be done in background

[bastiK]

...continued from #6137.

At the moment, we load images in EDT. When there is delay in the network, the user interface may block for some time. Instead, we should fetch the images asynchronously in a background thread.

[bastiK]

Replying to ​cmuelle8:

• First the preliminary icon is shown on the map, but when loading is finished, no repaint is done.

This should be solvable.

• The ElemStyles are cached and the preliminary Image causes wrong hash value. Consequently the wrong icon may be shown.

This really sucks. There is a comment in StyleCache I suppose you are refering to: "StyleCache must not be changed after it has been added to the intern pool." This would mitigate all efforts to do asynchronous resource loading.

Since resources effect hashCode calculation and hashCodes must not be manipulated after intern pool is built, we would have to wait building the intern pool until all resources are fetched.

Would it not suffice to just hash the name of the image? After all, if images use the same icon-image value in a style sheet, they evaluate to the same hashCode, just as the name values should, if they are identical. There would only be deviations to current behavior if a style writer uses the same image under different names - a case highly improbable.

You are right, it can be fixed relatively easy. The name is not enough, because there can be multiple zip archives that contain icons with the same name. See MapPaintStyles.IconReference class for a full description. My point was, that the patch doesn't quite work like this, but there is more to do...

[bastiK]

Replying to ​cmuelle8:

Replying to ​bastiK:

• First the preliminary icon is shown on the map, but when loading is finished, no repaint is done.

In MapPainter.java, function drawNodeIcon(), line

icon.paintIcon ( nc, g,   [...]

nc is used as a Component implementing ImageObserver. Maybe we can leverage this and use AWT functionality for asynchronous image loading, no need to write code twice.

Sure, whatever works best. No need to force it, though.

[bastiK]

In [4822/josm]:

make identity of map icons depend on the name and not the image data (see #6797)

[bastiK]

In [4823/josm]:

forgot to add (see #6797)

[bastiK]

First version. Should work, but is there a better (simpler) way to do this?