With this fix combined with fix to libsixel:
https://github.com/saitoha/libsixel/pull/170
browsing on slow machines (e.g., when floating-point calculation is
emulated by kernel) gets significantly speed up.
Note that if i->cache->a_width (i->cache->a_height) is zero, width
(height) should be set to zero. Otherwise, image in screen boundary
(i.e., partially displayed) becomes strangely resized.
Rin Okuyama