Fix PICT pixel decoding for 32-bit planar and cicn icons - #14
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Two decoding bugs in pict.py: 1. unpack4() used a 3-plane row stride (y*w*3) in the 4-plane (32-bit ARGB planar) branch, even though the buffer holds numplanes*w*h == 4*w*h bytes with rows 4*w wide. Any packtype-4 PICT with cmpcount==4 decoded with rows sliding out of alignment (scrambled colors/alpha). Use y*w*4 as the row base. 24-bit (3-plane) was already correct. 2. read_cicn() read the black-and-white icon bitmap using the mask bitmap's height (maskbm.height) instead of the B&W icon bitmap's own height. When the two BitMaps have different bounds, the unpacker advanced by the wrong byte count and the following read_colortable() read from the wrong offset, corrupting the palette. Use bwiconbm.height.
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Problem
Two decoding bugs in
pict.py:unpack4()uses a 3-plane row stride (y*w*3) in the 4-plane branch, even though the buffer holdsnumplanes*w*h == 4*w*hbytes with rows4*wwide. Any packtype-4 PICT withcmpcount == 4(32-bit ARGB planar) decodes with rows sliding out of alignment — colors/alpha bleed across rows. 24-bit (3-plane) was already correct.read_cicn()reads the black-and-white icon bitmap using the mask bitmap's height (maskbm.height) instead of the B&W icon's own (bwiconbm.height). When the two BitMaps have different bounds, the unpacker advances by the wrong byte count and the followingread_colortable()reads from the wrong offset, corrupting the palette.Fix
Use
y*w*4as the row base in the 4-plane branch, andbwiconbm.heightfor the B&W icon read.Prepared with Claude Fable 5 (Low effort mode). Automated finding, manually verified — please review before merging.