PreviewJob: handle previews bigger than 1024 in size
This does two things:
- set a default thumbdir, when the size requested does not fit in others, we could instead not cache the preview in those cases arguably.
- adds a xxx-large thumbdir, for preview bigger than 1024 in width or height.
The 2056 image-cache occurs when the users uses 512x512 previews on 2 dpr and doubles the size to make sure to have a better rendering, ending-up with a preview size of 2056.
A bigger size than strictly necessary allows to use downscaling instead of upscaling when rendering the image, which brings a higher level of details.
cc @broulik as you might be the right person to have a clue about this.
Edited by Méven Car