FxMaterialShowroomApp demo doesn't work from a read-only directory

I configure; ninja; ninja install.
Then I try to run the demo program FxMaterialShowroomApp from the installation directory, which might be read-only, for example /usr/bin. I get errors like:
Failed to save image: "No such file or directory"

If I copy the executable to a writable directory, then it runs.

Solution: The assets should be downloaded into a directory under the OS-specific temp space. On Linux mktemp -d would solve the issue.