DeprecatedFlyString relies heavily on DeprecatedString's StringImpl, so
let's rename it to A) match the name of DeprecatedString, B) write a new
FlyString class that is tied to String.
Name Trees are hierarchical, string-keyed, sorted-by-key dictionary
structures in PDF where each node (except the root) specifies the bounds
of the values it holds, and either its kids (more nodes) or the
key/value pairs it contains.
This commit implements a series of lookup calls for finding a key in
such name trees. This implementation follows the tree as needed on each
lookup, but if that becomes inefficient in the long run we can switch to
creating a HashMap with all the contents, which as a drawback will
require more memory.
With the StandardSecurityHandler the Length item in the Encryption
dictionary is optional, and needs to be given only if the encryption
algorithm (V) is other than 1; otherwise we can assume a length of 40
bits for the encryption key.
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).
For flate and lzw filters, the data can be transformed by this
predictor function to make it compress better. For us this means that
we have to undo this step in order to get the right result.
Although this feature is meant for images, I found at least a few
documents that use it all over the place, making this step very
important.
Previously we would draw all text, no matter what font type, as
Liberation Serif, which results in things like ugly character spacing.
We now have partial support for drawing Type 1 glyphs, which are part of
a PostScript font program. We completely ignore hinting for now, which
results in ugly looking characters at low resolutions, but gain support
for a large number of typefaces, including most of the default fonts
used in TeX.
Since PDF version 1.5, a document may omit the xref table in favor of
a new kind of xref stream object. This is used to reference so-called
"compressed" objects that are part of an object stream.
With this patch we are able to parse this new kind of xref object, but
we'll have to implement object streams to use them correctly.
Security handlers manage encryption and decription of PDF files. The
standard security handler uses RC4/MD5 to perform its crypto (AES as
well, but that is not yet implemented).
This is a big step, as most PDFs which are downloaded online will be
linearized. Pretty much the only difference is that the xref structure
is slightly different.
