A new checkbox in the toolbar now allows users toggle image rendering. A
corresponding Config option makes this setting non-volatile. To void
clashing with the previous "show_clipping_paths" option when caching a
Page, we now use the RenderingPreferences.hash() and the pair_int_hash
funcitons to compute a unique key into the page cache map for a given
RenderingPreferences and zoom level.
After adding support for XObject Form rendering, the next was to display
XObject images. This commit adds this initial support,
Images come in many shapes and forms: encodings: color spaces, bits per
component, width, height, etc. This initial support is constrained to
the color spaces we currently support, to images that use 8 bits per
component, to images that do *not* use the JPXDecode filter, and that
are not Masks. There are surely other constraints that aren't considered
in this initial support, so expect breakage here and there.
In addition to supporting images, we also support applying an alpha mask
(SMask) on them. Additionally, a new rendering preference allows to skip
image loading and rendering altogether, instead showing an empty
rectangle as a placeholder (useful for when actual images are not
supported). Since RenderingPreferences is becoming a bit more complex,
we add a hash option that will allow us to keep track of different
preferences (e.g., in a HashMap).
Interpolation is needed in more than one place, and I couldn't find a
central place where I could borrow a readily available interpolation
routine, so I've implemented the first simple interpolation object. More
will follow for more complex scenarios.
