read_orientation_helper() mapped the irot/imir properties to an EXIF
orientation with a list of conditions that misses several combinations,
e.g. a 90 degrees counterclockwise rotation followed by a mirroring,
which is how iPhone front-camera photos are stored. For those it still
returned true, so libheif was told to ignore the transformations while
Qt got no orientation either, and the image was shown sideways.
The orientation is now chosen by a switch on the rotation and, in each
case, on the mirroring, which is applied after the rotation as MIAF
requires. Other rotation values are left to libheif.
The new read tests cover the twelve rotation and mirroring combinations,
named like the AVIF ones. All of them display the same picture (colored
corners and an "F"): the stored pixels are that picture with the
transformations undone, written as uncompressed HEIF with libheif. Four
of them fail without this change.
