As mentioned in F.2.1.5 - Inverse DCT (IDCT), the decoder needs to
perform a level shift by adding 128. This used to be done in
`ycbcr_to_rgb` after the conversion. Now, we do it in `inverse_dct` in
order to ensure that the task is done unconditionally.
Consequences of this are that we are no longer required to explicitly
do it for RGB images and also, the `ycbcr_to_rgb` function is exactly
like the specification.
When reading the stream, interpreted as a normal value 0xF0 means skip
15 values and assign the 16th to 0. On the other hand, the marker ZRL
- which has the value 0xF0, means skip 16 values. For baseline JPEGs,
ZRL doesn't need to be interpreted differently as writing the 16th value
has no consequence. This is no longer the case with refining scans.
That's why this patch implement correctly ZRL.
We used to skip over zero coefficient by modifying the loop counter. It
is unfortunately impossible to perform this with SOF2 images as only
coefficients with a zero-history should be skipped.
This induces no behavior change for the user of the function.
This commit is nonsense for anything else than SOF2 images with spectral
approximation. For this particular case, skips like EOB or ZRL only
apply to coefficients with a zero-history. This commit prepares the code
to handle this behavior.
This function has probably been added when we weren't as good with error
propagations as we are now. We can safely remove it and let future
calls to `read` fail if the file is corrupted.
This can be tested with the following bytes (already used in 9191829a):
ffd8ffc000000800080ef701101200ffda00030100
Some fonts (like the Bootstrap Icons webfont) have bogus glyph offsets
in the `loca` table that point past the end of the `glyf` table.
AFAICT other rasterizers simply ignore these glyphs and treat them as if
they were missing. So let's do the same.
This makes https://changelog.serenityos.org/ actually work! :^)
The spec tells us that for glyph offsets in the "loca" table, if an
offset appears twice in a row, the index of the first one refers to a
glyph without an outline (such as the space character). We didn't check
for this, which would cause us to render a glyph outline where there
should have been nothing.
Introduced in 2c98eff, support for non-interleaved scans was not working
for frames with a number of MCU per line or column that is odd. Indeed,
the decoder assumed that they have scans that include a fabricated MCU
like scans with multiple components.
This patch makes the decoder handle images with a number of MCU per line
or column that is odd. To do so, as in the current decoder state we do
not know if components are interleaved at allocation time, we skip over
falsely-created macroblocks when filling them. As stated in 2c98eff,
this is probably not a good solution and a whole refactor will be
welcome.
It also comes with a test that open a square image with a side of 600px,
meaning 75 MCUs.
The `read_image_data` function of each one of[PBM, PGM, PPM]Loader use
the same structure to read an image. This patch harmonizes the three
functions and use finite loops instead of reading until EOF. It allows
to quit early on bloated file, but it's mainly done for refactoring
purpose.
The function signature goes from:
`bool read_number(Streamer& streamer, TValue* value)`
to
`ErrorOr<u16> read_number(Streamer& streamer)`
It allows us to, on one hand use `ErrorOr` for error propagation,
removing an out parameter in the meantime, and on the other hand remove
the useless template.
This is mostly a simple grayscale bilinear scale, with an extra step
of computing the distance and alpha with a little smoothing. This
can be used to paint more scalable UI elements/icons from rather
small distance fields. A tiny 16x16 SDF seems to do a decent job
for simple icons.
The stored ValueRecord in the font file only contains the fields
specified in the valueFormat field of the PairPosFormat1 table.
This means we need to construct the ValueRecord dynamically at runtime
and cannot bit_cast it to a struct.
read_value_record(u16 value_format, FixedMemoryStream& stream) takes
a bitmask value_format that describes the available fields of
the ValueRecord and a FixedMemoryStream at the location of the
next ValueRecord. It then advances the stream and returns a complete
ValueRecord.
At the moment, we only understand lookup type 2 (pair adjustment)
so let's ignore lookup tables with other types.
This fixes an issue where we'd choke on Noto Sans versions that come
with a chained context positioning lookup table (type 8).
Fixes#17924
This commit replaces usages of `Color::interpolate()` with
`Color::mixed_with()` in image scaling functions. The latter
uses premultiplied alpha, which results in more visually
pleasing edges when images are scaled against a transparent
background.
These changes affect the SmoothPixels and BilinearBlend scaling modes
of `Painter::draw_scaled_bitmap()` as well as the `Bitmap::scaled()`
function.
Fixes#17153.
This patch parses enough of GPOS tables to be able to support the
kerning information embedded in Inter.
Since that specific font only applies positioning offsets to the first
glyph in each pair, I was able to get away with not changing our API.
Once we start adding support for more sophisticated positioning, we'll
need to be able to communicate more than a simple "kerning offset" to
the clients of this code.
