This avoids the 404 errors that would previously result.

A compact encoding is used, with `!` plus the face letter used to specify a
new face, `>` plus a base83-encoded number used to specify a new level, and a
list of base83-encoded numbers used to specify x and y tile coordinates, where
the base83 encoding uses the minimum number of characters to encode the
maximum tile number for the level in question. The base83 encoding is the same
as the one used for SHT hashes.

Latest version of pyshtools uses Meson for building and does not build
in 20.04.

It now no longer works with Python <3.2.

This probably also speeds up the calculation.

WebGL 1 doesn't support REPEAT clamp mode for non-power-of-two images, which
is needed to avoid some rendering artifacts for small previews.

Spherical harmonic transform (SHT) previews are display instead of a solid
background color before the base multires tiles are loaded. If a thumbnail is
provided, it will be displayed instead of the SHT preview. If the thumbnail is
provided as a Base64-encoded string, the SHT preview may be briefly displayed,
since image loading is asynchronous, while the SHT preview is loaded
synchronously.

* Upgrade dockerfile to ubuntu 20.04

* Delete apt list files

Previously, one could generate a tile set that had the second level resolution
equal to the tile resolution, so it only had one tile per face.

Signed-off-by: Vanessa Sochat <vsochat@stanford.edu>

Signed-off-by: Vanessa Sochat <vsochat@stanford.edu>

Change computation of cube size - taking haov into account

* support also partial cubemap/fallback images: backgroundColor for missing face(s)

* extend multires/generate.py to cylindrical input and partial panoramas

* fixed a few typos in new help strings of generate.py

* Missing cubemap faces now need to be defined as null in the configuration

* made generate.py strict again on existing output directory, printing descriptive error message

* replaced unsafe eval by ast.literal_eval in generate.py

* a couple of minor improvements regarding 'undefined' in libpannellum.js

* made generate.py allow existing output directory in debug mode

for convenience, no need to delete output directory every time while testing

Extra dot in front of paths like 'path' and 'fallbackPath' are not necessary and may cause unexpected errors.

Replaces the os.system call for nona with a subprocess.check_call call
to get informed about errors when calling nona instead of silently
ignoring them before failing with missing files.