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Specification of LBA brick files (*.brk)
Abstract:the brick pixel data is run-length encoded and palette indexed.
Details:
*)***Run-length Encoding***
-the data is organized into rows
-every row is formed of several "runs"
a run is a sequence of pixels and defines what "comes
out" in the final pixel-based image.
-there are 3 forms of runs:
1. the skip run:
this run defines a sequence of pixels in the
final image which are NOT filled.
2. the color run:
this run defines a sequence of pixels in the
final image which are all set to the same color.
3. the copy run:
this run defines a sequence of pixels in the
final image which show no pattern an therefore
are copied directly.
now the actual algorithm:
for all rows do
read byte : number of runs
for number of runs do
read byte : run specification
extr. lowest 6 bits of run specification : run-length
run-length = runlength + 1
extr. bit #7 of run specification : color flag
extr. bit #8 of run specification : copy flag
if color flag is set
read byte : color
for run-length do
fill pixel with color
end for
else if copy flag is set
for run-length do
read byte : color
fill pixel with color
end for
else (both flags unset)
for run-length do
skip pixel
end for
end if
end for
end for
the run-lenth is always increased by one because a run-length of zero doesn't make sense.
*)***File Structure***
0. byte : offset X
1. byte : offset Y
2. byte : width
3. byte : height
following bytes: Run-length encoded data
(Specification provided by Omni)