Move the struct image_header and get_image_prop() into a header where we
can share these useful helpers between more test code. While doing that,
drop the unused field 'depth', rename into image_header_from(), and
introduce a helper to get u32 pointer to the beginning of a row. These
helpers should make pixel iterating code easier to read and safer (less
room for mistakes in address computations, and asserts).
Use the shared 'struct image_header' instead of the local one. The
intention is to make the code easier to read by using the same helpers
everywhere.
Width, height and stride use type 'int' because Pixman API uses that
too.
Signed-off-by: Pekka Paalanen <pekka.paalanen@collabora.com>
