A painted relief did not survive closing the project: nothing about the feature
was written to the .3mf, so the layers, their textures and the paint mask were
all lost on save. The layer struct's cereal save()/load() serve the undo/redo
stack only, which is one session and one binary stream.
Write the layer stack and the per-volume options as JSON in the archive, and
each layer's texture as the image file it was loaded from, both referenced by
path - the same split EmbossShape already makes for its SVG. The image stays
out of the XML deliberately: it is binary and routinely megabytes, and base64
in an attribute would bloat the one file every reader parses just to list the
objects. JSON rather than the cereal stream next to it because that one is
positional and unversioned, which would make every future field a
project-breaking change; an unknown key is ignored and a missing one keeps its
default, so a project written by either side keeps loading.
The paint masks go in as one attribute per layer slot, mirroring paint_color.
Older readers ignore attributes they do not know, so a project written here
still opens in a build without the feature - it loses the relief, which is all
it could have done with it anyway.
The layers are restored while the volume is being built rather than after the
archive is walked: volumes are constructed only once the whole archive has been
read, so a hook placed after the walk ran before any volume existed and
restored nothing.
ExPikaPaka
fcb1f62bd9