[PATCH] The image viewer for Geotagged images should not clear between pictures

[taylor.smock]

Expected behavior:
Screen does not flash between images

Current behavior (JOSM 14507):
Screen flashes "Loading <PICTURE>"

While the current behavior is OK when looking at very few images, when video mapping is used (​https://wiki.openstreetmap.org/wiki/Video_mapping), it can be hard on the eyes when quickly flipping through images.

Possible alternatives:
1) Leave currently loaded image up until the next image is ready, displaying a "Loading <picture>" below or in place of the current metadata, possibly ignoring further input (for the image viewer) until the image is ready.
2) Preload the next <n> images to avoid loading from disk

[Don-vip]

2) is addressed by #4172

[zlavergne]

Replying to Don-vip:

2) is addressed by #4172

Has this had any headway? It looks like it's been inactive for 5 years.

[taylor.smock]

Don't clear set image to null when the next entry is not null

[taylor.smock]

So I finally got around to looking into this more, and it turns out we (a) always set the new image to null when a new image is set and then (b) immediately call repaint(). This patch only sets the image to null if the new ImageEntry is null.

So far, in my usage, it seems to be working well.

[taylor.smock]

TODO:

• Get the error messages showing up with an appropriate background. See ​https://github.com/JOSM/Mapillary/commit/ba2ef1d0deb78a1436e320663db3ade6de237919 and ​https://github.com/JOSM/Mapillary/commit/9ea9106015b08bd167d0c3c82f3a197380237774 .

[taylor.smock]

Add option to have background of error text show up (disabled by default -- can be hard on the eyes), properly show loading/error text

[taylor.smock]

What the new patch does:

• Does not set the image to null when the new ImageEntry (in setImage) is not null. This avoids clearing the screen (thus causing a white flash, since the next image is almost always immediately loaded).
• Adds a new setting geoimage.message.error.background, which defaults to false to avoid a flashing white section of the screen. This affects how the error messages are displayed.
• Adds a field to keep track of the old ImageEntry so that an appropriate message can be shown (does oldImageEntry == imageEntry? If so, we have loaded the image and don't have to show a loading message)
• Draw the image first and the messages second (otherwise, the image would overwrite the error text)

[taylor.smock]

Patch ping

[taylor.smock]

Patch ping.

[simon04]

In 17783/josm:

fix #17072 - Geotagged images viewer should not clear between pictures (patch by taylor.smock)