🚀 go-pugleaf

Here it is.  (This came out on INFO-MAC several months ago).
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For those interested, here is a description of the format of MACpaint files.
This format is the common interchange format for full-page bitmap images on
the MACintosh.

The first 512 bytes of the file are the header. The first four bytes comprise
the version number, followed by 38*8 = 304 bytes of patterns.  The remaining
204 bytes of the header are reserved for future expansion. If the version
number is zero, the patterns are ignored. Hence, programs that wish to create
files to be read into MACpaint can just write out 512 bytes of zero as the
header.

Following the header are 720 compressed scanlines of data which form the 576
wide by 720 tall bitmap. The bitmap is compressed as follows ;

Any run of three or more equal bytes is compressed into a count byte and a
single data byte. Runs of unequal bytes are passed on literally, preceded also
by a count byte. I.E.

<count byte> <data byte>    count = -1..-127 --> replicate byte 2..128 times
<count byte> <n data bytes> count =  0.. 127 --> copy 1..128 bytes uncompressed
                            count = -128 ignored for backward compatibility

That's it. A nice simple scheme. Thanks to Bill Atkinson for providing this
info.