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Update comments and fix some bugs

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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
This commit is contained in:
kris
2019-07-11 23:40:00 +01:00
parent 722e9c5d70
commit f3d03a1b87
13 changed files with 623 additions and 403 deletions
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601
transcoder/screen.py
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@@ -14,7 +14,7 @@ IntOrArray = Union[np.uint64, np.ndarray]
def y_to_base_addr(y: int, page: int = 0) -> int:
"""Maps y coordinate to base address on given screen page"""
"""Maps y coordinate to base address on given screen page."""
a = y // 64
d = y - 64 * a
b = d // 8
@@ -126,33 +126,44 @@ class MemoryMap:
class Bitmap:
"""Packed 28-bit bitmap representation of (D)HGR screen memory.
"""Packed bitmap representation of (D)HGR screen memory.
XXX comments
The memory layout is still page-oriented, not linear y-x buffer but the
bit map is such that 20 consecutive entries linearly encode the 28*20 =
560-bit monochrome dot positions that underlie both Mono and Colour (
D)HGR screens.
For Colour display the (nominal) colours are encoded as 4-bit pixels.
Maintains a page-based array whose entries contain a packed representation
of multiple screen bytes, in a representation that supports efficiently
determining the visual effect of storing bytes at arbitrary screen offsets.
"""
# NOTE: See https://github.com/numpy/numpy/issues/2524 and related issues
# for why we have to cast things explicitly to np.uint64 - type promotion
# to uint64 is broken in numpy :(
# Name of bitmap type
NAME = None # type: str
# Size of packed representation
# Size of packed representation, consisting of header + body + footer
HEADER_BITS = None # type: np.uint64
BODY_BITS = None # type: np.uint64
FOOTER_BITS = None # type: np.uint64
# How many bits of packed representation are necessary to determine the
# effect of storing a memory byte, e.g. because they influence pixel
# colour or are influenced by other bits.
MASKED_BITS = None # type: np.uint64
# How many coloured screen pixels we can extract from MASKED_BITS. Note
# that this does not include the last 3 dots represented by the footer,
# since we don't have enough information to determine their colour (we
# would fall off the end of the 4-bit sliding window)
MASKED_DOTS = None # type: np.uint64
# List of bitmasks for extracting the subset of packed data corresponding
# to bits influencing/influenced by a given byte offset. These must be
# a contiguous bit mask, i.e. so that after shifting they are enumerated
# by 0..2**MASKED_BITS-1
BYTE_MASKS = None # type: List[np.uint64]
BYTE_SHIFTS = None # type: List[np.uint64]
# How many bits of packed representation are influenced when storing a
# memory byte
MASKED_BITS = None # type: np.uint64
# XXX
# NTSC clock phase at first masked bit
PHASES = None # type: List[int]
def __init__(
@@ -176,18 +187,21 @@ class Bitmap:
shape=(32, 128), dtype=np.uint64) # type: np.ndarray
self._pack()
def _body(self) -> np.ndarray:
raise NotImplementedError
# TODO: don't leak headers/footers across screen rows. We should be using
# x-y representation rather than page-offset
@staticmethod
def _make_header(prev_col: IntOrArray) -> IntOrArray:
def _make_header(col: IntOrArray) -> IntOrArray:
"""Extract values to use as header of next column."""
raise NotImplementedError
def _body(self) -> np.ndarray:
"""Pack related screen bytes into an efficient representation."""
raise NotImplementedError
@staticmethod
def _make_footer(next_col: IntOrArray) -> IntOrArray:
def _make_footer(col: IntOrArray) -> IntOrArray:
"""Extract values to use as footer of previous column."""
raise NotImplementedError
def _pack(self) -> None:
@@ -195,17 +209,15 @@ class Bitmap:
body = self._body()
# XXX comments
# Prepend last 3 bits of previous main odd byte so we can correctly
# decode the effective colours at the beginning of the 28-bit
# tuple
# Prepend last 3 bits of previous odd byte so we can correctly
# decode the effective colours at the beginning of the 22-bit tuple
prev_col = np.roll(body, 1, axis=1).astype(np.uint64)
header = self._make_header(prev_col)
# Don't leak header across page boundaries
header[:, 0] = 0
# Append first 3 bits of next aux even byte so we can correctly
# decode the effective colours at the end of the 28-bit tuple
# Append first 3 bits of next even byte so we can correctly
# decode the effective colours at the end of the 22-bit tuple
next_col = np.roll(body, -1, axis=1).astype(np.uint64)
footer = self._make_footer(next_col)
# Don't leak footer across page boundaries
@@ -218,20 +230,27 @@ class Bitmap:
byte_offset: int,
old_value: IntOrArray,
new_value: np.uint8) -> IntOrArray:
"""Update int/array to store new value at byte_offset in every entry.
Does not patch up headers/footers of neighbouring columns.
"""
raise NotImplementedError
@staticmethod
@functools.lru_cache(None)
def byte_offset(x_byte: int, is_aux: bool) -> int:
def byte_offset(page_offset: int, is_aux: bool) -> int:
"""Map screen offset for aux/main into offset within packed data."""
raise NotImplementedError
@staticmethod
@functools.lru_cache(None)
def _byte_offsets(is_aux: bool) -> Tuple[int, int]:
"""Return byte offsets within packed data for AUX/MAIN memory."""
raise NotImplementedError
@classmethod
def to_dots(cls, masked_val: int, byte_offset: int) -> int:
"""Convert masked representation to bit sequence of display dots."""
raise NotImplementedError
def apply(
@@ -254,6 +273,7 @@ class Bitmap:
page: int,
offset: int,
byte_offset: int) -> None:
"""Fix up column headers/footers when updating a (page, offset)."""
if byte_offset == 0 and offset > 0:
self.packed[page, offset - 1] = self._fix_column_left(
@@ -272,6 +292,8 @@ class Bitmap:
column_left: IntOrArray,
column: IntOrArray
) -> IntOrArray:
"""Patch up the footer of the column to the left."""
# Mask out footer(s)
column_left &= np.uint64(2 ** (self.HEADER_BITS + self.BODY_BITS) - 1)
column_left ^= self._make_footer(column)
@@ -283,6 +305,8 @@ class Bitmap:
column_right: IntOrArray,
column: IntOrArray
) -> IntOrArray:
"""Patch up the header of the column to the right."""
# Mask out header(s)
column_right &= np.uint64(
(2 ** (self.BODY_BITS + self.FOOTER_BITS) - 1)) << self.HEADER_BITS
@@ -295,15 +319,19 @@ class Bitmap:
ary: np.ndarray,
byte_offset: int
) -> None:
"""Fix up column headers/footers for all array entries."""
# TODO: don't leak header/footer across page boundaries
# Propagate new value into neighbouring byte headers/footers if
# necessary
if byte_offset == 0:
# Need to also update the 3-bit footer of the preceding column
# Need to also update the footer of the preceding column
shifted_left = np.roll(ary, -1, axis=1)
self._fix_column_left(ary, shifted_left)
elif byte_offset == 3:
# Need to also update the 3-bit header of the next column
elif byte_offset == (self.SCREEN_BYTES - 1):
# Need to also update the header of the next column
shifted_right = np.roll(ary, 1, axis=1)
self._fix_column_right(ary, shifted_right)
@@ -340,22 +368,25 @@ class Bitmap:
cls,
data: IntOrArray,
byte_offset: int) -> IntOrArray:
"""Masks and shifts data into the MASKED_BITS range."""
"""Masks and shifts packed data into the MASKED_BITS range."""
res = (data & cls.BYTE_MASKS[byte_offset]) >> (
cls.BYTE_SHIFTS[byte_offset])
assert np.all(res <= 2 ** cls.MASKED_BITS)
return res
# Can't cache all possible values but this seems to give a good enough hit
# rate without costing too much memory
# TODO: unit tests
@functools.lru_cache(None)
@functools.lru_cache(10 ** 6)
def byte_pair_difference(
self,
byte_offset: int,
old_packed: np.uint64,
content: np.uint8
) -> np.uint16:
old_pixels = self.mask_and_shift_data(
old_packed, byte_offset)
"""Compute effect of storing a new content byte within packed data."""
old_pixels = self.mask_and_shift_data(old_packed, byte_offset)
new_pixels = self.mask_and_shift_data(
self.masked_update(byte_offset, old_packed, content), byte_offset)
@@ -368,15 +399,24 @@ class Bitmap:
source: "Bitmap",
is_aux: bool
) -> np.ndarray:
"""Compute edit distance matrix from source bitmap."""
return self._diff_weights(source.packed, is_aux)
# TODO: unit test
def _diff_weights(
self,
source_packed: np.ndarray,
is_aux: bool,
content: np.uint8 = None
) -> np.ndarray:
"""Computes diff from source_packed to self.packed"""
"""Computes edit distance matrix from source_packed to self.packed
If content is set, the distance will be computed as if this value
was stored into each offset position of source_packed, i.e. to
allow evaluating which offsets (if any) should be chosen for storing
this content byte.
"""
diff = np.ndarray((32, 256), dtype=np.int)
offsets = self._byte_offsets(is_aux)
@@ -384,63 +424,173 @@ class Bitmap:
dists = []
for o in offsets:
if content is not None:
source_packed = self.masked_update(o, source_packed, content)
self._fix_array_neighbours(source_packed, o)
compare_packed = self.masked_update(o, source_packed, content)
self._fix_array_neighbours(compare_packed, o)
else:
compare_packed = source_packed
# Pixels influenced by byte offset o
source_pixels = self.mask_and_shift_data(source_packed, o)
source_pixels = self.mask_and_shift_data(compare_packed, o)
target_pixels = self.mask_and_shift_data(self.packed, o)
# Concatenate 13-bit source and target into 26-bit values
# Concatenate N-bit source and target into 2N-bit values
pair = (source_pixels << self.MASKED_BITS) + target_pixels
dist = self.edit_distances(self.palette)[o][pair].reshape(
pair.shape)
dists.append(dist)
# Interleave even/odd columns
diff[:, 0::2] = dists[0]
diff[:, 1::2] = dists[1]
return diff
def _check_consistency(self):
"""Sanity check that headers and footers are consistent."""
headers = np.roll(self._make_header(self.packed), 1, axis=1).astype(
np.uint64)
footers = np.roll(self._make_footer(self.packed), -1, axis=1).astype(
np.uint64)
mask_hf = np.uint64(0b1110000000000000000000000000000111)
res = (self.packed ^ headers ^ footers) & mask_hf
nz = np.transpose(np.nonzero(res))
ok = True
if nz.size != 0:
for p, o in nz.tolist():
if o == 0 or o == 127:
continue
ok = False
print(p, o, bin(self.packed[p, o - 1]),
bin(headers[p, o]),
bin(self.packed[p, o]),
bin(self.packed[p, o + 1]), bin(footers[p, o]),
bin(res[p, o])
)
assert ok
# TODO: unit tests
def compute_delta(
self,
content: int,
old: np.ndarray,
diff_weights: np.ndarray,
is_aux: bool
) -> np.ndarray:
# TODO: use error edit distance
"""Compute which content stores introduce the least additional error.
diff = self._diff_weights(self.packed, is_aux, content)
We compute the effect of storing content at all possible offsets
within self.packed, and then subtract the previous diff weights.
Negative values indicate that the new content value is closer to the
target than the current content.
"""
# TODO: use error edit distance?
new_diff = self._diff_weights(self.packed, is_aux, content)
# TODO: try different weightings
return (diff * 5) - old
return (new_diff * 5) - diff_weights
class HGRBitmap(Bitmap):
"""Packed bitmap representation of HGR screen memory.
The HGR display is encoded in a somewhat complicated way, so we have to
do a bit of work to turn it into a useful format.
Each screen byte consists of a palette bit (7) and 6 data bits (0..6)
Each non-palette bit turns on two consecutive display dots, with bit 6
repeated a third time. This third dot may or may not be overwritten by the
effect of the next byte.
Turning on the palette bit shifts that byte's dots right by one
position.
Given two neighbouring screen bytes Aaaaaaaa, Bbbbbbbb (at even and odd
offsets), where capital letter indicates the position of the palette bit,
we use the following 22-bit packed representation:
2211111111110000000000 <-- bit position in uint22
1098765432109876543210
ffFbbbbbbbBAaaaaaaaHhh
h and f are headers/footers derived from the neighbouring screen bytes.
Since our colour artifact model (see colours.py) uses a sliding 4-bit window
onto the dot string, we need to also include a 3-bit header and footer
to account for the influence from/on neighbouring bytes, i.e. adjacent
packed values. These are just the low/high 2 data bits of the 16-bit
body of those neighbouring columns, plus the corresponding palette bit.
This 22-bit packed representation is sufficient to compute the effects
(on pixel colours) of storing a byte at even or odd offsets. From it we
can extract the bit stream of displayed HGR dots, and the mapping to pixel
colours follows the HGRColours bitmap, see colours.py.
We put the two A/B palette bits next to each other so that we can
mask a contiguous range of bits whose colours influence/are influenced by
storing a byte at a given offset.
We need to mask out bit subsequences of size 3+8+3=14, i.e. the 8-bits
corresponding to the byte being stored, plus the neighbouring 3 bits that
influence it/are influenced by it.
Note that the masked representation has the same size for both offsets (
14 bits), but different meaning, since the palette bit is in a different
position.
With this masked representation, we can precompute an edit distance for the
pixel changes resulting from all possible HGR byte stores, see
make_edit_distance.py.
The edit distance matrix is encoded by concatenating the 14-bit source
and target masked values into a 28-bit pair, which indexes into the
edit_distance array to give the corresponding edit distance.
"""
NAME = 'HGR'
# hhhbbbbbbbpPBBBBBBBfff
# 0000000011111111111111
# 1111111111111100000000
# Size of packed representation, consisting of header + body + footer
HEADER_BITS = np.uint64(3)
# 2x 8-bit screen bytes
BODY_BITS = np.uint64(16)
FOOTER_BITS = np.uint64(3)
# Header:
# 0000000010000011
# Footer:
# 1100000100000000
# How many bits of packed representation are necessary to determine the
# effect of storing a memory byte, e.g. because they influence pixel
# colour or are influenced by other bits.
MASKED_BITS = np.uint64(14) # 3 + 8 + 3
# How many coloured screen pixels we can extract from MASKED_BITS. Note
# that this does not include the last 3 dots represented by the footer,
# since we don't have enough information to determine their colour (we
# would fall off the end of the 4-bit sliding window)
#
# From header: 3 bits (2 HGR pixels but might be shifted right by palette)
# From body: 7 bits doubled, plus possible shift from palette bit
MASKED_DOTS = np.uint64(18) # 3 + 7 + 7
# List of bitmasks for extracting the subset of packed data corresponding
# to bits influencing/influenced by a given byte offset. These must be
# a contiguous bit mask, i.e. so that after shifting they are enumerated
# by 0..2**MASKED_BITS-1
BYTE_MASKS = [
np.uint64(0b0000000011111111111111),
np.uint64(0b1111111111111100000000)
]
BYTE_SHIFTS = [np.uint64(0), np.uint64(8)]
MASKED_BITS = np.uint64(14) # 3 + 8 + 3
HEADER_BITS = np.uint64(3)
# 7-bits doubled, plus possible shift from palette bit
BODY_BITS = np.uint64(15)
FOOTER_BITS = np.uint64(3)
# NTSC clock phase at first masked bit
#
# Each HGR byte offset has the same range of uint14 possible
# values and nominal colour pixels, but with different initial
# phases:
# even: 0 (1 at start of 3-bit header)
# odd: 2 (3)
PHASES = [1, 3]
def __init__(self, palette: pal.Palette, main_memory: MemoryMap):
@@ -448,10 +598,11 @@ class HGRBitmap(Bitmap):
@staticmethod
def _make_header(col: IntOrArray) -> IntOrArray:
# Header format is bits 5,6,0 of previous byte
# i.e. offsets 16, 17, 11
"""Extract values to use as header of next column.
# return (col & np.uint64(0b111 << 16)) >> np.uint64(16)
Header format is bits 5,6,0 of previous screen byte
i.e. offsets 17, 18, 11 in packed representation
"""
return (
(col & np.uint64(0b1 << 11)) >> np.uint64(9) ^ (
@@ -459,11 +610,13 @@ class HGRBitmap(Bitmap):
)
def _body(self) -> np.ndarray:
# Body is in order
# a0 a1 a2 a3 a4 a5 a6 a7 b7 b0 b1 b2 b3 b4 b5 b6
# so that a) the header and footer have the same order
# across the two byte offsets, and b) so that they
# can be extracted as contiguous bit ranges
"""Pack related screen bytes into an efficient representation.
Body is of the form:
bbbbbbbBAaaaaaaa
where capital indicates the palette bit.
"""
even = self.main_memory.page_offset[:, 0::2].astype(np.uint64)
odd = self.main_memory.page_offset[:, 1::2].astype(np.uint64)
@@ -474,133 +627,46 @@ class HGRBitmap(Bitmap):
@staticmethod
def _make_footer(col: IntOrArray) -> IntOrArray:
# Footer format is bits 7,0,1 of next byte
# i.e. offsets 10,3,4
"""Extract values to use as footer of previous column.
Footer format is bits 7,0,1 of next screen byte
i.e. offsets 10,3,4 in packed representation
"""
return (
(col & np.uint64(0b1 << 10)) >> np.uint64(10) ^ (
(col & np.uint64(0b11 << 3)) >> np.uint64(2))
) << np.uint64(19)
# # XXX move to make_data_tables
# def _pack(self) -> None:
# """Pack main memory into (28+3)-bit uint64 array"""
#
# # 00000000001111111111222222222233
# # 01234567890123456789012345678901
# # AAAABBBBCCCCDDd
# # AAAABBBBCCCCDd
# # DDEEEEFFFFGGGGg
# # dDDEEEEFFFFGGGg
#
# # Even, P0: store unshifted (0..14)
# # Even, P1: store shifted << 1 (1..15) (only need 1..14)
#
# # Odd, P0: store shifted << 14 (14 .. 28) - set bit 14 as bit 0 of next
# # byte
# # Odd, p1: store shifted << 15 (15 .. 29) (only need 15 .. 28) - set
# # bit 13 as bit 0 of next byte
#
# # Odd overflow only matters for even, P1
# # - bit 0 is either bit 14 if odd, P0 or bit 13 if odd, P1
# # - but these both come from the undoubled bit 6.
#
# main = self.main_memory.page_offset.astype(np.uint64)
#
# # Double 7-bit pixel data from a into 14-bit fat pixels, and extend MSB
# # into 15-bits tohandle case when subsequent byte has palette bit set,
# # i.e. is right-shifted by 1 dot. This only matters for even bytes
# # with P=0 that are followed by odd bytes with P=1; in other cases
# # this extra bit will be overwritten.
# double = (
# # Bit pos 6
# ((main & 0x40) << 8) + ((main & 0x40) << 7) + (
# (main & 0x40) << 6)) + (
# # Bit pos 5
# ((main & 0x20) << 6) + ((main & 0x20) << 5)) + (
# # Bit pos 4
# ((main & 0x10) << 5) + ((main & 0x10) << 4)) + (
# # Bit pos 3
# ((main & 0x08) << 4) + ((main & 0x08) << 3)) + (
# # Bit pos 2
# ((main & 0x04) << 3) + ((main & 0x04) << 2)) + (
# # Bit pos 1
# ((main & 0x02) << 2) + ((main & 0x02) << 1)) + (
# # Bit pos 0
# ((main & 0x01) << 1) + (main & 0x01))
#
# a_even = main[:, ::2]
# a_odd = main[:, 1::2]
#
# double_even = double[:, ::2]
# double_odd = double[:, 1::2]
#
# # Place even offsets at bits 1..15 (P=1) or 0..14 (P=0)
# packed = np.where(a_even & 0x80, double_even << 1, double_even)
#
# # Place off offsets at bits 15..27 (P=1) or 14..27 (P=0)
# packed = np.where(
# a_odd & 0x80,
# np.bitwise_xor(
# np.bitwise_and(packed, (2 ** 15 - 1)),
# double_odd << 15
# ),
# np.bitwise_xor(
# np.bitwise_and(packed, (2 ** 14 - 1)),
# double_odd << 14
# )
# )
#
# # Patch up even offsets with P=1 with extended bit from previous odd
# # column
#
# previous_odd = np.roll(a_odd, 1, axis=1).astype(np.uint64)
#
# packed = np.where(
# a_even & 0x80,
# # Truncate to 28-bits and set bit 0 from bit 6 of previous byte
# np.bitwise_xor(
# np.bitwise_and(packed, (2 ** 28 - 2)),
# (previous_odd & (1 << 6)) >> 6
# ),
# # Truncate to 28-bits
# np.bitwise_and(packed, (2 ** 28 - 1))
# )
#
# # Append first 3 bits of next even byte so we can correctly
# # decode the effective colours at the end of the 28-bit tuple
# trailing = np.roll(packed, -1, axis=1).astype(np.uint64)
#
# packed = np.bitwise_xor(
# packed,
# (trailing & 0b111) << 28
# )
#
# self.packed = packed
@staticmethod
@functools.lru_cache(None)
def byte_offset(x_byte: int, is_aux: bool) -> int:
"""Returns 0..1 offset in packed representation for a given x_byte."""
assert not is_aux
def byte_offset(page_offset: int, is_aux: bool) -> int:
"""Returns 0..1 offset in packed representation for page_offset."""
is_odd = x_byte % 2 == 1
assert not is_aux
is_odd = page_offset % 2 == 1
return 1 if is_odd else 0
@staticmethod
@functools.lru_cache(None)
def _byte_offsets(is_aux: bool) -> Tuple[int, int]:
"""Return byte offsets within packed data for AUX/MAIN memory."""
assert not is_aux
return 0, 1
@staticmethod
@functools.lru_cache(None)
def _double_pixels(int7: int) -> int:
"""Each bit 0..6 controls two hires dots.
# Input bit 6 is repeated 3 times in case the neighbouring byte is
# delayed (right-shifted by one dot) due to the palette bit being set.
# Care needs to be taken to mask this out when overwriting.
Input bit 6 is repeated 3 times in case the neighbouring byte is
delayed (right-shifted by one dot) due to the palette bit being set,
which means the effect of this byte is "extended" by an extra dot.
Care needs to be taken to mask this out when overwriting.
"""
double = (
# Bit pos 6
((int7 & 0x40) << 8) + ((int7 & 0x40) << 7) + (
@@ -608,32 +674,38 @@ class HGRBitmap(Bitmap):
# Bit pos 5
((int7 & 0x20) << 6) + ((int7 & 0x20) << 5) +
# Bit pos 4
((int7 & 0x10) << 5) + ((int7 & 0x10) << 4) + (
# Bit pos 3
((int7 & 0x08) << 4) + ((int7 & 0x08) << 3) +
# Bit pos 2
((int7 & 0x04) << 3) + ((int7 & 0x04) << 2) +
# Bit pos 1
((int7 & 0x02) << 2) + ((int7 & 0x02) << 1) +
# Bit pos 0
((int7 & 0x01) << 1) + (int7 & 0x01))
((int7 & 0x10) << 5) + ((int7 & 0x10) << 4) +
# Bit pos 3
((int7 & 0x08) << 4) + ((int7 & 0x08) << 3) +
# Bit pos 2
((int7 & 0x04) << 3) + ((int7 & 0x04) << 2) +
# Bit pos 1
((int7 & 0x02) << 2) + ((int7 & 0x02) << 1) +
# Bit pos 0
((int7 & 0x01) << 1) + (int7 & 0x01)
)
return double
@classmethod
def to_dots(cls, masked_val: int, byte_offset: int) -> int:
"""Convert masked representation to bit sequence of display dots.
Packed representation is of the form:
ffFbbbbbbbBAaaaaaaaHhh
where capital indicates the palette bit.
Each non-palette bit turns on two display dots, with bit 6 repeated
a third time. This may or may not be overwritten by the next byte.
Turning on the palette bit shifts that byte's dots right by one
position.
"""
# Assert 14-bit representation
assert (masked_val & (2 ** 14 - 1)) == masked_val
# Unpack hhHaaaaaaaABbbbbbbbFff
# --> hhhaaaaaaaaaaaaaabbbb (P=0, P=0, P=0)
# hhhaaaaaaaaaaaaaabbbb (P=1, P=0, P=0)
# hhhhaaaaaaaaaaaaabbbb (P=1, P=1, P=0)
# hhhhaaaaaaaaaaaaaabbb (P=1, P=1, P=1)
# Take top 3 bits from header (plus duplicated MSB) not 4, because if it
# is palette-shifted then we don't know what is in bit 0
h = (masked_val & 0b111) << 5
@@ -641,11 +713,11 @@ class HGRBitmap(Bitmap):
res = cls._double_pixels(h & 0x7f) >> (11 - hp)
if byte_offset == 0:
# Offset 0: hhHaaaaaaaABbb
# Offset 0: bbBAaaaaaaaHhh
b = (masked_val >> 3) & 0xff
bp = (b & 0x80) >> 7
else:
# Offset 1: aaABbbbbbbbFff
# Offset 1: ffFbbbbbbbBAaa
bp = (masked_val >> 3) & 0x01
b = ((masked_val >> 4) & 0x7f) ^ (bp << 7)
@@ -664,7 +736,6 @@ class HGRBitmap(Bitmap):
res ^= cls._double_pixels(f & 0x7f) << (17 + fp)
return res & (2 ** 21 - 1)
# XXX test
@staticmethod
def masked_update(
byte_offset: int,
@@ -694,37 +765,99 @@ class HGRBitmap(Bitmap):
class DHGRBitmap(Bitmap):
# NOTE: See https://github.com/numpy/numpy/issues/2524 and related issues
# for why we have to cast things explicitly to np.uint64 - type promotion
# to uint64 is broken in numpy :(
"""Packed bitmap representation of DHGR screen memory.
The DHGR display encodes 7 pixels across interleaved 4-byte sequences
of AUX and MAIN memory, as follows:
PBBBAAAA PDDCCCCB PFEEEEDD PGGGGFFF
Aux N Main N Aux N+1 Main N+1 (N even)
Where A..G are the pixels, and P represents the (unused) palette bit.
This layout makes more sense when written as a (little-endian) 32-bit
integer:
33222222222211111111110000000000 <- bit pos in uint32
10987654321098765432109876543210
PGGGGFFFPFEEEEDDPDDCCCCBPBBBAAAA
i.e. apart from the palette bits this is a linear ordering of pixels,
when read from LSB to MSB (i.e. right-to-left). i.e. the screen layout
order of bits is opposite to the usual binary representation ordering.
We can simplify things by stripping out the palette bit and packing
down to a 28-bit integer representation:
33222222222211111111110000000000 <- bit pos in uint32
10987654321098765432109876543210
GGGGFFFFEEEEDDDDCCCCBBBBAAAA <- pixel A..G
3210321032103210321032103210 <- bit pos in A..G pixel
3333333222222211111110000000 <- byte offset 0.3
Since our colour artifact model (see colours.py) uses a sliding 4-bit window
onto the dot string, we need to also include a 3-bit header and footer
to account for the influence from/on neighbouring bytes, i.e. adjacent
packed values. These are just the low/high 3 bits of the 28-bit body of
those neighbouring columns.
This gives a 34-bit packed representation that is sufficient to compute
the effects (on pixel colours) of storing a byte at one of the 0..3 offsets.
Note that this representation is also 1:1 with the actual displayed
DHGR dots. The mapping to pixel colours follows the DHGRColours
bitmap, see colours.py.
Because the packed representation is contiguous, we need to mask out bit
subsequences of size 3+7+3=13, i.e. the 7-bits corresponding to the
byte being stored, plus the neighbouring 3 bits that influence it/are
influenced by it.
With this masked representation, we can precompute an edit distance for the
pixel changes resulting from all possible DHGR byte stores, see
make_edit_distance.py.
The edit distance matrix is encoded by concatenating the 13-bit source
and target masked values into a 26-bit pair, which indexes into the
edit_distance array to give the corresponding edit distance.
"""
NAME = 'DHGR'
# 3-bit header + 28-bit body + 3-bit footer
BYTE_MASKS = [
# 3333333222222211111110000000 <- byte 0.3
#
# 3333222222222211111111110000000000 <- bit pos in uint64
# 3210987654321098765432109876543210
# tttGGGGFFFFEEEEDDDDCCCCBBBBAAAAhhh <- pixel A..G
# 3210321032103210321032103210 <- bit pos in A..G pixel
np.uint64(0b0000000000000000000001111111111111), # byte 0 int13 mask
np.uint64(0b0000000000000011111111111110000000), # byte 1 int13 mask
np.uint64(0b0000000111111111111100000000000000), # byte 2 int13 mask
np.uint64(0b1111111111111000000000000000000000), # byte 3 int13 mask
]
# How much to right-shift bits after masking to bring into int13 range
BYTE_SHIFTS = [np.uint64(0), np.uint64(7), np.uint64(14), np.uint64(21)]
# Packed representation is 3 + 28 + 3 = 34 bits
HEADER_BITS = np.uint64(3)
BODY_BITS = np.uint64(28)
FOOTER_BITS = np.uint64(3)
MASKED_BITS = np.uint64(13)
# Masked representation selecting the influence of each byte offset
MASKED_BITS = np.uint64(13) # 7-bit body + 3-bit header + 3-bit footer
# Masking is 1:1 with screen dots, but we can't compute the colour of the
# last 3 dots because we fall off the end of the 4-bit sliding window
MASKED_DOTS = np.uint64(10)
# 3-bit header + 28-bit body + 3-bit footer
BYTE_MASKS = [
# 3333222222222211111111110000000000 <- bit pos in uint64
# 3210987654321098765432109876543210
# tttGGGGFFFFEEEEDDDDCCCCBBBBAAAAhhh <- pixel A..G
# 3210321032103210321032103210 <- bit pos in A..G pixel
#
# 3333333222222211111110000000 <- byte offset 0.3
np.uint64(0b0000000000000000000001111111111111), # byte 0 uint13 mask
np.uint64(0b0000000000000011111111111110000000), # byte 1 uint13 mask
np.uint64(0b0000000111111111111100000000000000), # byte 2 uint13 mask
np.uint64(0b1111111111111000000000000000000000), # byte 3 uint13 mask
]
# How much to right-shift bits after masking, to bring into uint13 range
BYTE_SHIFTS = [np.uint64(0), np.uint64(7), np.uint64(14), np.uint64(21)]
# NTSC clock phase at first masked bit
# Each DHGR byte offset has the same range of int13 possible
#
# Each DHGR byte offset has the same range of uint13 possible
# values and nominal colour pixels, but with different initial
# phases:
# AUX 0: 0 (1 at start of 3-bit header)
@@ -733,19 +866,27 @@ class DHGRBitmap(Bitmap):
# MAIN 1: 1 (2)
PHASES = [1, 0, 3, 2]
@staticmethod
def _make_header(col: IntOrArray) -> IntOrArray:
"""Extract upper 3 bits of body for header of next column."""
return (col & np.uint64(0b111 << 28)) >> np.uint64(28)
def _body(self) -> np.ndarray:
"""Pack related screen bytes into an efficient representation.
For DHGR we first strip off the (unused) palette bit to produce
7-bit values, then interleave aux and main memory columns and pack
these 7-bit values into 28-bits. This sequentially encodes 7 4-bit
DHGR pixels, which is the "repeating unit" of the DHGR screen, and
in a form that is convenient to operate on.
We also shift to make room for the 3-bit header.
"""
# Palette bit is unused for DHGR so mask it out
aux = (self.aux_memory.page_offset & 0x7f).astype(np.uint64)
main = (self.main_memory.page_offset & 0x7f).astype(np.uint64)
# XXX update
# Interleave aux and main memory columns and pack 7-bit masked values
# into a 28-bit value, with 3-bit header and footer. This
# sequentially encodes 7 4-bit DHGR pixels, together with the
# neighbouring 3 bits that are necessary to decode artifact colours.
#
# See make_data_tables.py for more discussion about this representation.
return (
(aux[:, 0::2] << 3) +
(main[:, 0::2] << 10) +
@@ -753,11 +894,6 @@ class DHGRBitmap(Bitmap):
(main[:, 1::2] << 24)
)
@staticmethod
def _make_header(col: IntOrArray) -> IntOrArray:
"""Extract upper 3 bits of body for header of next column."""
return (col & np.uint64(0b111 << 28)) >> np.uint64(28)
@staticmethod
def _make_footer(col: IntOrArray) -> IntOrArray:
"""Extract lower 3 bits of body for footer of previous column."""
@@ -765,9 +901,10 @@ class DHGRBitmap(Bitmap):
@staticmethod
@functools.lru_cache(None)
def byte_offset(x_byte: int, is_aux: bool) -> int:
"""Returns 0..3 packed byte offset for a given x_byte and is_aux"""
is_odd = x_byte % 2 == 1
def byte_offset(page_offset: int, is_aux: bool) -> int:
"""Returns 0..3 packed byte offset for a given page_offset and is_aux"""
is_odd = page_offset % 2 == 1
if is_aux:
if is_odd:
return 2
@@ -781,6 +918,8 @@ class DHGRBitmap(Bitmap):
@staticmethod
@functools.lru_cache(None)
def _byte_offsets(is_aux: bool) -> Tuple[int, int]:
"""Return byte offsets within packed data for AUX/MAIN memory."""
if is_aux:
offsets = (0, 2)
else:
@@ -790,8 +929,11 @@ class DHGRBitmap(Bitmap):
@classmethod
def to_dots(cls, masked_val: int, byte_offset: int) -> int:
# For DHGR the 13-bit masked value is already a 13-bit dot sequence
# so no need to transform it.
"""Convert masked representation to bit sequence of display dots.
For DHGR the 13-bit masked value is already a 13-bit dot sequence
so no need to transform it.
"""
return masked_val
@@ -804,7 +946,6 @@ class DHGRBitmap(Bitmap):
Does not patch up headers/footers of neighbouring columns.
"""
# Mask out 7-bit value where update will go
masked_value = old_value & (
~np.uint64(0x7f << (7 * byte_offset + 3)))