display errors with width greater than 32768 pixels (15bit)

[Philipp Gassmann]

When I open an image with more than 32'768 pixel in width, the won't display the pixels > 32'768
This is the case when combining multiple XX Megapixels images to a Panorama.
Tried wide image in tif and jpg format.

32768 is 2^15, 16bit.

Affects multiple tools. Shotwell is a special case, where it affects only certain zoom levels.

[Philipp Gassmann (phiphi.g)]

Problem identified on upstream bug report:
https://bugzilla.gnome.org/show_bug.cgi?id=163090#c18

Cyril Roussillon wrote on 2012-01-10 01:01:27 UTC

Very annoying for panoramas indeed.

I had a look, and the problem is in the scaling functions in
gdk-pixbuf/pixops/pixops.c : the constant SCALE_SHIFT which is set to 16.

So for instance in function pixops_process when you execute:

  run_end_x = (((src_width - filter->x.n + 1) << SCALE_SHIFT) -
scaled_x_offset);

with src_width > 32768 and run_end_x of type int, you get an overflow.

What I did as a temporary local workaround is to define SCALE_SHIFT to 12
instead of 16, but a cleaner fix would probably be to use gint64 variables
instead of int wherever it is necessary (as it only affects local variables).

Hope this could motivate a developer to fix it properly...