requiring callers to keep track of it
- stop trying to cache content_deltas, I think it results in losing
deltas. Instead just recompute the deltas for each page as we need
it. This is fast enough in practice.
- track the average fill rate for the additional offsets we emit.
This should be close to 3 if we're succeeding in finding enough
collateral work
- overhaul how we pass in the target memory maps. The previous way
didn't make sense: we weren't actually encoding for the target video
frame, but were using an inconsistent mix of old and new frames. I
think this was causing image artifacting because we were aiming for
the wrong thing.
- Add some debugging assertions that were used to track this down.
requiring callers to keep track of it
- stop trying to cache content_deltas, I think it results in losing
deltas. Instead just recompute the deltas for each page as we need
it. This is fast enough in practice.
- track the average fill rate for the additional offsets we emit.
This should be close to 3 if we're succeeding in finding enough
collateral work
- overhaul how we pass in the target memory maps. The previous way
didn't make sense: we weren't actually encoding for the target video
frame, but were using an inconsistent mix of old and new frames. I
think this was causing image artifacting because we were aiming for
the wrong thing.
- Add some debugging assertions that were used to track this down.
For some reason playback speed is only about 1.6x (probably due to
slowing down accesses to the I/O page to 1MHz, so as not to mess up
hardware timings), but happily this comes within 3% of being 44100/2.
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
It doesn't functionally matter since I'm not using any conditional
opcodes in the fast path anyway, but STA removes these side-effects.
Earlier I had mistakenly thought that STA absolute did a
read-before-write on 6502, but this is not the case
(verified with visual6502.org)
- 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.
- For HGRBitmap introduce a packed representation in the form
hhHaaaaaaaABbbbbbbbFff where capitals indicate the location of the
palette bit. i.e. for header and footer we include the neighbouring
2 data bits as in DHGR but also the palette bit from that byte, which
is necessary to understand how these data bits unpack into dots.
The nonstandard ordering of the palette bit for the odd data byte (B)
is so that the masking by byte offset produces a contiguous sequence
of bits, i.e. the 14-bit masked representation is still dense.
- Introduce a to_dots() classmethod that converts from the masked bit
representation of dots influenced by a screen byte to the actual
sequence of screen dots. For DHGR this is the identity map since
there are no shenanigans with palette bits causing dots to shift
around.
- Add a bunch more unit tests, and add back the Sather tests for HGR
artifact colours from palette bit interference, which now all pass!
- Reduce the size of the precomputed edit distance matrix by half by
exploiting the fact that it is symmetrical under
i << N + j <-> j << N + i where N is the size of the masked bit
representation (i.e. transposing the original (i, j) -> dist
metric matrix).
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
