One additional fix for the gimp-channel-combine-masks procedure,
it needs both the combined *and* combined-to buffer in
gimp_gegl_mask_combine_buffer() to be treated specially.
Storing selections and layer masks as linear grayscale, but channels
as whatever-the-layers-are caused severe problems in images with
gamma-corrected layers: when combining channels with the selection,
they would go thorugh a gamma conversion before being combined, giving
unexpected results.
This commit changes all channels to always be linear, except in 8-bit
images, where they continue to be "Y' u8", for compatibility with old
XCF files, and because linear 8-bit can't really be used in
compositing (channels can be visible too).
To fix channel -> selection combinations also for these images, add a
small hack to gimp_gegl_mask_combine_buffer() which makes sure the
to-be-combined channel's pixels are always read as-is, without any
gamma conversion. After changing channels to linear, this makes no
difference except in the 8-bit images where we need this hack.
- don't include <gdk-pixbuf/gdk-pixbuf.h> in headers in app/
- instead, include it in many .c files instead of <glib-object.h>,
finally acknowledging the fact that app/ depends on gdk-pixbuf almost
globally
- fix up includes as if libgimpbase depended in GIO, which it soon will
The new by-row iteration doesn't re-write the length
value for each row. In general it is not safe to modify
the iterator data because the internal logic depends
on the public data, but this specific case is new.
