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.
The existing try_create_from_serialized_byte_buffer function accepts a
ByteBuffer, but in reality it requires only a ReadonlyBytes, since
internally the only thing it does is calling buffer.bytes(). There is
thus no reason to have a function that simply accepts ReadonlyBytes, and
implement the former in terms of the newer.
Arrays of float numbers are common in many PDF objects, and thus to
avoid code repetition I'm introducing a new method to ArrayObject that
will return exactly that.
ColorSpaces now can tell users how many components they expect, and the
default decode array that should be used when converting unit bit
sequences into color space component input values during image
rendering.
