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841a95c56a
Save the tested release workflows, RAM media processing, program discovery, FLIRT library, and shared-object maintenance. Add Git exclusions, file attributes, and instructions for a later push using a forwarded SSH agent.
71 lines
3.3 KiB
Python
71 lines
3.3 KiB
Python
"""Bounded indexed DMD bitmap decoding, including keyframe-dependent delta frames.
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Grammar recovered from named GOT 1.37 functions (binary SHA-256 637acf6d...):
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image_alloc_and_decompress_{column,row}_whitespace, row_16, and
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image_get_keyframe_and_decompress_{column,row}_delta. See docs/decoder-evidence.md.
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Returns exact indices; palette/application compositing is separate.
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"""
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import struct
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FORMATS={0:'raw-indexed8',1:'column-whitespace',3:'column-delta',7:'row-whitespace',9:'row-delta',12:'row-indexed4'}
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def decode(record, keyframes):
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if len(record)<13:raise ValueError('truncated DMD record')
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identity,flags,width,height=struct.unpack_from('<IIHH',record)
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size=width*height;mode=record[12];pos=13
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if not 0<width<=4096 or not 0<height<=4096 or size>16777216:raise ValueError('DMD dimensions exceed bound')
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if mode not in FORMATS:raise ValueError(f'unsupported DMD encoding {mode}')
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base=None
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if mode in (3,9):
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base=next((keyframes[k] for k in ((identity-1)&0xffff,identity&0xffff) if k in keyframes and keyframes[k][0:2]==(width,height)),None)
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if base is None:raise ValueError('DMD delta lacks matching preceding keyframe')
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pixels=bytearray(base[2])
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else:pixels=bytearray(size)
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cursor=0
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def take(n):
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nonlocal pos
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if n<0 or pos+n>len(record):raise ValueError('truncated DMD packet')
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data=record[pos:pos+n];pos+=n;return data
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def write(values):
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nonlocal cursor
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if cursor+len(values)>size:raise ValueError('DMD packet exceeds pixel bounds')
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if mode not in (1,3):
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pixels[cursor:cursor+len(values)]=values;cursor+=len(values)
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else:
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start=0
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while start<len(values):
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count=min(height-cursor%height,len(values)-start)
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offset=(cursor%height)*width+cursor//height
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pixels[offset:offset+count*width:width]=values[start:start+count]
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cursor+=count;start+=count
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if mode==0:
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pixels[:]=take(size);cursor=size
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elif mode==12:
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packed=bytes(take((size+1)//2))
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pixels[0::2]=packed.translate(bytes(value&15 for value in range(256)))
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pixels[1::2]=packed[:size//2].translate(bytes(value>>4 for value in range(256)))
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cursor=size
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else:
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while True:
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token=take(1)[0]
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if token==0:break
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if mode in (3,9):
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if token>=128:
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cursor+=256-token
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if cursor>size:raise ValueError('DMD delta skip exceeds bounds')
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else:write(take(token))
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else:
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count=token>>2;kind=token&3
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if not count:raise ValueError('empty DMD whitespace packet')
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if kind==0:write(take(count))
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elif kind in (1,2):write(bytes([0 if kind==1 else 15])*count)
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else:write(bytes(take(1))*count)
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if cursor!=size:raise ValueError('DMD packet did not cover complete frame')
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result=bytes(pixels)
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if mode in (3,9):
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keyframes.pop((identity-1)&0xffff,None)
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keyframes[identity&0xffff]=(width,height,result)
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elif flags&4:
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keyframes[identity&0xffff]=(width,height,result)
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return {'pixels':result,'consumed':pos,'format':FORMATS[mode],'mode':mode,'width':width,'height':height,'record_id':identity,'flags':flags,'base_record':(identity-1)&0xffff if base else None}
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