WIN: Show Focus Point display has unsharp/blurry image or even aborts ("Export to disk failed. No thumbnail received").

[capricorn8]

On Windows, when the plugin is invoked in Develop mode (File -> Plugin Extra -> Show Focus Point), it can happen that

1. the focus point is displayed on an unsharp/blurry image, or
2. the focus point window does not even come up but an error message instead "Export to disk failed. No thumbnail received"

Reason:
The windows implementation of the plugin uses a function of the Lightroom SDK (photo:requestJpegThumbnail) that returns a preview image of the selected photo. Previews get created / loaded only in Library module.

1. When Lightroom is started with empty caches, and the plugin is invoked for a photo in Develop module, for which the preview has not been created but not yet loaded, the Focus Point Viewer will display a blurry image.
2. When an image is cropped and a new preview has not been created, invoking the plugin in Develop module will cause an error message: "Export to disk failed. No thumbnail received"

Workaround:

• if any of the two situation happens, switch to Library module for a short moment (preview gets created) then back to Develop module.

Alternatively, you can avoid these issues altogether if you do not invoke the plugin in Develop module but only in Library module.