256 color PCX reader, 2

 BBS: Inland Empire Archive
Date: 11-21-92 (13:57)             Number: 394
From: HARRY GISH                   Refer#: NONE
  To: ALL                           Recvd: NO  
Subj: 256 color PCX reader, 2        Conf: (2) Quik_Bas

"Now we position at the 128th byte, which is where the data begins."

RECORD#2,128

"Read a byte"

"Decode a group"
READ#2,X$;1:X=ASC(X$):Bytes#=Bytes#+1

"Now we must see if the byte represents a single color value or if it is a"
"multiplier value. A quirk of 256 color PCX's is that a single value of the"
"top 64 colors must be encoded as a multiplier of 1 times
the color. You can't"
"say COLOR 255, you must say 1 times 255. This makes many 256 color PCX files"
"actually larger than a simple value dump. In this case if the byte value is"
"less than 193 then it is an actual value."

LONGIFX<193
COLORX:PLOTPointer,Line
Pointer=Pointer+1
ENDIF

"Otherwise we interpret it as a multiplier. Multiplier value can be as large"
"as 63."

LONGIFX>192
X=X-192:READ#2,X$;1:Y=ASC(X$):Bytes#=Bytes#+1
COLORY:PLOTPointer,LineTOPointer+X-1,Line
Pointer=Pointer+X
ENDIF

"Pointer notes the current position in the X line scan. When the line is done"
"Pointer gets reset to zero."

IFPointer<XResGOTO"Decode a group"
Pointer=0

"If we're at line end of now we need to see if all lines are decoded. If so"
"we end, otherwise we start processing the next line."

IFLine=YResGOTO"End"

Line=Line+1
GOTO"Decode a group"

"End"
WHILEINKEY$="":WEND
MODE3:COLOR15,1,4:CLS:END

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