From:	"A.Appleyard" <A DOT APPLEYARD AT fs2 DOT mt DOT umist DOT ac DOT uk>
To:	DJGPP AT SUN DOT SOE DOT CLARKSON DOT EDU
Date:	Fri, 9 Jun 1995 16:03:15 BST
Subject:	Paintbrush or similar: anyone got a source for it?

  The `Paintbrush' package in Windows, or anything similar which can change
individual pixels: please has anyone got a complete source form of it?, so
that I can add to it some features of my own that I would like to add. I
suppose that I could write my own completely from scratch; but that would take
a lot of my time.

  With thanks to R DOT Exler AT jk DOT uni-linz DOT ac DOT at for useful information: here is how
to write your own black-and-white PCX file:-

int wide = <<desired width in pixels>>, high = <<desired height in pixels>>;
FILE*F <<must be opened in BINARY mode>>;
/* typedef struct {unsigned char r,g,b;} color; */
/*-----*/
struct PCXheader { /* 128 bytes */
    unsigned char ID,version,code,bitsperplane;
    unsigned short X0,Y0,X1,Y1,XDPI,YDPI;
    /* color color16[16]; */ char color[48]; /* palette */
    /* best declared that way to be sure that the compiler won't insert a
       4th byte after each set of 3 */
    unsigned char reserved,planes; short bytesperline,palettetype;
    char unused[58];} H;
/*-----*/
H.ID=10; H.version=5; H.code=H.bitsperplane=1; H.reserved=0; H.planes=1;
H.X0=H.Y0=0; H.X1=wide-1; H.Y1=high-1;
H.XDPI=300; H.YDPI=300; /* theoretical pixels per inch in X and in Y */
H.bytesperline=(wide+7)/8; H.palettetype=1;
for(j=0;j<3;j++) H.color[j]=255; for(j=3;j<6;j++) H.color[j]=0;
/* But I suspect that the palette is ignored */
for(i=0;i<58;i++) H.unused[i]=0;

fwrite(&H,1,128,F);

  Then a bitmap of each row left to right in turn from the top down. At the
end of each row, fill to right with unused bits to complete the last byte; but
it is best if `wide' is a multiple of 8. You must represent blank paper by a 1
bit, drawing by a 0 bit, not vice versa (else Word Perfect, Windows Write, etc
drawing the picture out will ink the background and not the drawing!) In this
mode, one byte represents 8 pixels.
  If n adjacent bytes are all the same (n < 64), they can be replaced by one
copy of that byte, preceded by the byte (0xc0+n). But don't use this repeating
to compress across the boundary between two lines.
  Therefore, if an unrepeated picture byte starts with two 1 bytes, (i.e.
(B&0xc0)==0xc0), to show that it is a picture byte and not a repeat counter,
you must insert the byte 0xc1 before it (= `repeat once').

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