make_edit_distance
- use MASKED_DOTS since it does not have a simple relationship to the
HEADER_BITS/BODY_BITS for HGR
- try disabling transposition distances for Damerau-Levenshtein, this
may give better quality
screen
- introduce separate notion of MASKED_DOTS which is the number of
(coloured) pixels we can extract from MASKED_BITS. For HGR this is
not the same.
- fix bug in _fix_array_neighbours that was not fixing headers for HGR
- don't cache everything in byte_pair_differences, it's effectively
unbounded. Using 1M for LRU size seems to work just as well in
practise, without leaking memory.
- fix bug in _diff_weights when comparing content, we want to evaluate
the effect of storing content byte in each offset separately, not
cumulatively.
- add a consistency check function (not currently wired up) to assert
that headers/footers are in sync across columns
- HGR should have 16 body bits, this was causing headers not to
propagate correctly to/from neighbouring column
- add test case for this bug
video
- Use 8 random bits consistently, using 16 in some places may have
introduced bias
- ignore palette bit when comparing 0x00 and 0x7f in sanity check
- Only compute the upper triangle since the matrix is symmetrical and
we can reconstruct the rest cheaply at load time
- Compute edit distances for HGR as well by making use of the fact that
the masked representation is 14-bit but still sparse.
- Add sanity checks for various invariants of the edit distance matrices.
packed representation (diff, apply etc). This allows the (D)HGRBitmap
classes to focus on the bitmap packing and share common logic.
Numpy has unfortunate long-standing bugs to do with type coercion of
np.uint64, which leads to spurious "incompatible type" warnings when
e.g. operating on a np.uint64 and some other integer type. To work
around this we cast explicitly to np.uint64 everywhere.
Get tests working again - for now HGR tests in screen_test.py are
disabled until I finish implementing new packing.
HGRBitmap is still incomplete although closer.
- naive version of NTSC artifacting, it uses a sliding 4-bit window to
assign a nominal (D)HGR colour to each dot position. A more
sophisticated/correct implementation would model the YIQ signal
directly.
- Switch DHGRBitmap implementation to use a 34-bit representation of
the 4-byte tuple, comprised of a 3-bit header and footer, plus
4*7=28-bit body. The headers/footers account for the influence on
neighbouring tuples from the 4-bit NTSC window.
- With this model each screen byte influences 13 pixels, so we need to
precompute 2^26 edit distances for all possible (source, target)
13-bit sequences.
- Checkpointing not-yet-working HGR implementation.
- Add new unit tests but not yet all passing due to refactoring
IIGS palettes.
Move the palette diff_matrix generation into make_data_tables.py since
that is the only place it is used.
Demand-load the edit distance matrices when transcoding.
(3-pixel) sequences that may be modified when storing bytes to the
DHGR display.
This relies on producing an efficient linear representation of the
DHGR framebuffer in terms of a packed 28-bit representation of (Aux,
Main, Aux, Main) screen bytes.
