PsL Monthly 1993 December/PSL Monthly Shareware CD-ROM (December 1993).iso/prgmming/dos/pascal/pcxkit.exe/PCX.PAS

Pascal/Delphi Source File | 1992-03-26 | 23.0 KB | 628 lines

unit PCX;

(* version 3.1
                             by Peter Donnelly
                              1301 Ryan Street
                                Victoria BC
                               Canada V8T 4Y8

   ╒══════════════════════════════════════════════════════════════════════╕
   │    May be copied freely. If you make practical use of this unit,     │
   │         a contribution of $10 or more would be appreciated.          │
   ╘══════════════════════════════════════════════════════════════════════╛

   This is a unit to read .PCX files and put them in displayable form. The
   actual work of decoding the file and moving the data into memory is done
   in assembler. Version 6 of Turbo Pascal is required for compilation.

   The following display modes are supported:

          Mode      TP GraphMode     Resolution    Colors
          ~~~~      ~~~~~~~~~~~~     ~~~~~~~~~~    ~~~~~~
          $04       CGAC0 to C3      320 x 200         4
          $06       CGAHi            640 x 200         2
          $0D        ---             320 x 200        16
          $0E       EGALo/VGALo      640 x 200        16
          $10       EGAHi/VGAMed     640 x 350        16
          $12       VGAHi            640 x 480        16
          $13        ---             320 x 200       256

   Mode $13 is supported only for files containing palette information,
   i.e. not those produced by versions of Paintbrush earlier than 3.0.

   The unit has been optimized for speed rather than flexibility or
   compactness. In particular, the routine for displaying 16-color files
   (which require the most computation) has been improved and now runs
   about 50 percent faster than that in version 2.

   It is assumed that the image is the width of and no taller than the
   screen, and that you will set the correct display mode. No checking
   is done to see that the .PCX file is compatible with the mode you've set.
   You do, however, have to pass in the Turbo GraphDriver as a parameter
   for all but 256-color files, so that the data will be interpreted
   correctly. (For mode $0D, pass in 'EGA' or 'VGA', and see the comment on
   palettes, below.)

   For the CGA formats, the data is put into two buffers on the heap, from
   where it can be moved into the two display memory banks. See SHOWCGA for
   an example. You can of course alter the unit to move the data directly
   into display memory, but there is no great saving in time.

   For EGA and VGA formats, the data is written to page 0 of the video
   buffer. This can easily be changed by setting "page_addr" to a different
   value. Three different techniques of hiding the image while it is being
   written are demonstrated in SHOWEGA, SHOWVGA, and SHOW256. If for any
   reason you don't want to do this, you will want to rewrite the palette-
   interpretation routines as separate procedures so you can set the
   palette before decoding the image data.

   References:
   ~~~~~~~~~~
   Richard F. Ferraro, "Programmer's Guide to the EGA and VGA Cards"
   (Addison-Wesley, 1988).

   Richard Wilton, "Programmer's Guide to PC and PS/2 Video Systems"
   (Microsoft, 1987).

   "Technical Reference Manual [for Paintbrush]" (Zsoft, 1988). The
   information in this booklet is also found in a file distributed with
   at least some versions of Microsoft/PC Paintbrush.

   Software:
   ~~~~~~~~
   Besides the various incarnations of Paintbrush (ZSoft and Microsoft),
   the excellent Deluxe Paint II Enhanced (Electronic Arts) can also create
   files in .PCX format. Other graphics programs have conversion utilities.
*)

{ ======================================================================= }

INTERFACE

uses DOS, GRAPH;

type    RGBrec = record
                   redval, greenval, blueval: byte;
                 end;

var     pcxfilename: pathstr;
        file_error: boolean;
        pal: palettetype;
        RGBpal: array[0..15] of RGBrec;
        RGB256: array[0..255] of RGBrec;
        page_addr: word;
        bytes_per_line: word;
        buff0, buff1: pointer;

        { CGA display memory banks: }
        screenbuff0: array[0..7999] of byte absolute $b800:$0000;
        screenbuff1: array[0..7999] of byte absolute $b800:$2000;

const   page0 = $A000;           { EGA/VGA display segment }

procedure SETMODE(mode: byte);
procedure SETREGISTERS(var palrec);
procedure READ_PCX_FILE(gdriver: integer; pfilename: pathstr);
procedure READ_PCX256(pfilename: pathstr);

{========================================================================}

IMPLEMENTATION

var     scratch, abuff0, abuff1: pointer;
        is_CGA, is_VGA: boolean;
        repeatcount: byte;
        datalength: word;
        columncount, plane, video_index: word;
        regs: registers;

const   buffsize = 65521;   { Largest possible }

{ -------------------------- BIOS calls --------------------------------- }

{ For modes not supported by the BGI, use SetMode to initialize the
  graphics. Since SetRGBPalette won't work if Turbo hasn't done the
  graphics initialization itself, use SetRegisters to change the colors
  in mode $13. }

procedure SETMODE(mode: byte);

begin
regs.ah:= 0;                 { BIOS set mode function }
regs.al:= mode;              { Display mode }
intr($10, regs);             { Call BIOS }
end;

procedure SETREGISTERS(var palrec);

{ Palrec is any string of 768 bytes containing the RGB data. }

begin
regs.ah:= $10;               { BIOS color register function }
regs.al:= $12;               { Subfunction }
regs.es:= seg(palrec);       { Address of palette info. }
regs.dx:= ofs(palrec);
regs.bx:= 0;                 { First register to change }
regs.cx:= $100;              { Number of registers to change }
intr($10, regs);             { Call BIOS }
end;

{ ====================== EGA/VGA 16-color files ========================= }

procedure DECODE_16; assembler;

asm

(* Registers used:

   AL   data byte to be written to video
   AH   data bytes per scan line
   BX   end of input buffer
   CL   number of times data byte is to be written
   DL   current column in scan line
   ES   output segment
   DI   index into output buffer
   DS   segment of input buffer
   SI   index into input buffer
   BP   current color plane
*)

push    bp

{ ----------------- Assembler procedure for 16-color files -------------- }

{ The first section is initialization done on each run through the
  input buffer. }

@startproc:
mov     bp, plane           { plane in BP }
mov     es, page_addr       { video display segment }
mov     di, video_index     { index into video segment }
mov     ah, byte ptr bytes_per_line  { line length in AH }
mov     dx, columncount     { column counter }
mov     bx, datalength      { no. of bytes to read }
xor     cx, cx              { clean up CX for loop counter }
mov     cl, repeatcount     { count in CX }
push    ds                  { save DS }
lds     si, scratch         { input buffer pointer in DS:SI }
 { We have to adjust datalength for comparison with SI. TP 6.0 pointers are
   normalized, but the offset can still be 0 or 8. }
add     bx, si
cld                         { clear DF for stosb }
cmp     cl, 0               { was last byte a count? }
jne     @multi_data         { yes, so next is data }
jmp     @getbyte            { no, so find out what next is }

{ -------------- Procedure to write EGA/VGA image to video -------------- }

{ The data in the .PCX file is organized by color plane, by line; that is,
  all the data for plane 0 for line 1, then for plane 1, line 1, etc.
  Writing the data to display memory is just a matter of masking out the
  other planes while one plane is being written to. This is done with the
  map mask register in the sequencer. All the other weird and wonderful
  registers in the EGA/VGA do just fine with their default settings, thank
  goodness. }

@writebyte:
stosb                       { AL into ES:DI, inc DI }
inc     dl                  { increment column }
cmp     dl, ah              { reached end of scanline? }
je      @doneline           { yes }
loop    @writebyte          { no, do another }
jmp     @getbyte            {   or get more data }
@doneline:
shl     bp, 1               { shift to next plane }
cmp     bp, 8               { done 4 planes? }
jle     @setindex           { no }
mov     bp, 1               { yes, reset plane to 1 but don't reset index }
jmp     @setplane
@setindex:
sub     di, dx              { reset to start of line }
@setplane:
push    ax                  { save AX }
cli                         { no interrupts }
mov     ax, bp              { plane is 1, 2, 4, or 8 }
mov     dx, 3C5h            { sequencer data register }
out     dx, al              { mask out 3 planes }
sti                         { enable interrupts }
pop     ax                  { restore AX }
xor     dx, dx              { reset column count }
loop    @writebyte          { do it again, or fetch more data }

{ -------------------- Loop through input buffer ------------------------ }

{ Here's how the data compression system works. Each byte is either image
  data or a count byte that tells how often the next byte is to be
  repeated. The byte is image data if it follows a count byte, or if
  either of the top 2 bits is clear. Otherwise it is a count byte, with
  the count derived from the lower 6 bits. }

@getbyte:                   { last byte was not a count }
cmp     si, bx              { end of input buffer? }
je      @exit               { yes, quit }
lodsb                       { get a byte from DS:SI into AL, increment SI }
cmp     al, 192             { test high bits }
jb      @one_data           { not set, it's data to be written once }
 { It's a count byte: }
xor     al, 192             { get count from 6 low bits }
mov     cl, al              { store repeat count }
cmp     si, bx              { end of input buffer? }
je      @exit               { yes, quit }
@multi_data:
lodsb                       { get data byte }
jmp     @writebyte          { write it CL times }
@one_data:
mov     cl, 1               { write byte once }
jmp     @writebyte

{ ---------------------- Finished with buffer --------------------------- }

@exit:
pop     ds                  { restore Turbo's data segment }
mov     plane, bp           { save status for next run thru buffer }
mov     repeatcount, cl
mov     columncount, dx
mov     video_index, di
pop     bp
end;  { asm }

{ ===================== CGA 2- and 4-color files ======================== }

procedure DECODE_CGA; assembler;

asm

(* Registers used:

   AL   data byte to be written to video
   AH   data bytes per scan line
   BX   end of input buffer
   CL   number of times data byte is to be written
   DL   pointer to current column in screen row
   ES   output segment; temporarily used for input buffer segment
   DI   index into output buffer
   SI   index into input buffer
   BP   current video bank
*)

push    bp
jmp     @startproc

{ ------------- Procedure to store CGA image in buffers ----------------- }

@storebyte:
stosb                       { AL into ES:DI, increment DI }
inc     dx                  { increment column count }
cmp     dl, ah              { reached end of line? }
je      @row_ends           { yes }
loop    @storebyte          { not end of row, do another byte }
ret
@row_ends:
xor     bp, 1               { switch banks }
cmp     bp, 1               { is bank 1? }
je      @bank1              { yes }
mov     word ptr abuff1, di { no, save index into bank 1 }
les     di, abuff0          { bank 0 pointer into ES:DI }
xor     dx, dx              { reset column counter }
loop    @storebyte
ret
@bank1:
mov     word ptr abuff0, di { save index into bank 0 }
les     di, abuff1          { bank 1 pointer into ES:DI }
xor     dx, dx              { reset column counter }
loop    @storebyte
ret

{ ---------------- Main assembler procedure for CGA --------------------- }

{ It's assumed that CGA files will require only one pass through the
  input buffer. }

@startproc:
mov     bp, 0                        { bank in BP }
mov     es, word ptr abuff0[2]       { segment of bank 0 buffer }
mov     di, word ptr abuff0          { offset of buffer }
mov     ah, byte ptr bytes_per_line  { line length in AH }
mov     bx, datalength               { no. of bytes to read }
xor     cx, cx                       { clean up CX for loop counter }
xor     dx, dx                       { initialize column counter }
mov     si, dx                       { initialize input index }
cld                                  { clear DF for stosb }

{ -------------------- Loop through input buffer ------------------------ }

@getbyte:
cmp     si, bx              { end of input buffer? }
je      @exit               { yes, quit }
push    es                  { save output pointer }
push    di
les     di, scratch         { get input pointer in ES:DI }
add     di, si              { add current offset }
mov     al, [es:di]         { get a byte }
inc     si                  { advance input index }
pop     di                  { restore output pointer }
pop     es
cmp     cl, 0               { was previous byte a count? }
jg      @multi_data         { yes, this is data }
cmp     al, 192             { no, test high bits }
jb      @one_data           { not set, not a count }
 { It's a count byte: }
xor     al, 192             { get count from 6 low bits }
mov     cl, al              { store repeat count }
jmp     @getbyte            { go get data byte }
@one_data:
mov     cl, 1               { write byte once }
call    @storebyte
jmp     @getbyte
@multi_data:
call    @storebyte          { CL already set }
jmp     @getbyte

{ ---------------------- Finished with buffer --------------------------- }

@exit:
pop     bp
end;  { asm }

{ ============= Main procedure for CGA and 16-color files =============== }

procedure READ_PCX_FILE(gdriver: integer; pfilename: pathstr);

type    ptrrec = record
                   segm, offs: word;
                 end;

var     entry, gun, pcxcode, mask, colorID: byte;
        palbuf: array[0..66] of byte;
        pcxfile: file;

begin   { READ_PCX_FILE }
is_CGA:= (gdriver = CGA);   { 2 or 4 colors }
is_VGA:= (gdriver = VGA);   { 16 of 256K possible colors }
                            { Otherwise EGA - 16 of 64 possible colors }
assign(pcxfile, pfilename);
{$I-} reset(pcxfile, 1);  {$I+}
file_error:= (IOresult <> 0);
if file_error then exit;

{ To minimize disk access and speed things up, we read the file into a
  scratchpad on the heap. Large files have to be done in two or more
  chunks because of the 64K limit on dynamic memory variables. }

getmem(scratch, buffsize);                 { Allocate scratchpad }
blockread(pcxfile, scratch^, 128);         { Get header into scratchpad }

{ The .PCX file has a 128-byte header. Most of it can be ignored if you're
  working with a known format. All we want is the palette information and
  the length of the data line. }

move(scratch^, palbuf, 67);
bytes_per_line:= palbuf[66];

{------------------------ Setup for CGA ---------------------------------}

if is_CGA then
begin
  getmem(buff0, 8000);      { Allocate memory for output }
  getmem(buff1, 8000);
  abuff0:= buff0;           { Make copies of pointers }
  abuff1:= buff1;
end else

{----------------------- Setup for EGA/VGA ------------------------------}

begin
  video_index:= 0;
  port[$3C4]:= 2;           { Index to map mask register }
  plane:= 1;                { Initialize plane }
  port[$3C5]:= plane;       { Set sequencer to mask out other planes }

{-------------------- Decipher EGA/VGA palette --------------------------}

(* The palette information is stored in bytes 16-63 of the header. Each of
   the 16 palette slots is allotted 3 bytes - one for each primary color.
   Any of these bytes can have a value of 0-255.

   For the EGA there are just 4 significant settings, since only 64
   different colors (4 x 4 x 4) are available. Hence for EGA-format images
   we divide the codes by 64. The absolute color number for the palette
   entry is derived by setting one of bits 0-2 and one of bits 3-5 with the
   mask corresponding to the .PCX code byte. (In binary form, the absolute
   color number may be thought of as 00RGBrgb.) This number is then passed
   into Turbo's SetAllPalette procedure.

   For the VGA things work differently. Here we must use Turbo's
   SetRGBPalette procedure to change the red, green, and blue values in the
   16 active color registers. The registers expect values in the range 0-63
   (64 x 64 x 64 = 256K, the number of possible colors), so we divide the
   .PCX codes by 4. A further complication is that by default the palette
   entries point to the color registers corresponding to the standard EGA
   colors, so we must change them to point to registers 0-15 instead (or
   else modify registers 0-5, 20, 7, and 56-63). See SHOWVGA.PAS for an
   example of how to set the palette and the registers.

   Note that the palette works differently for the 200-line 16-color modes,
   $0D and $0E. Because these modes use 4-bit palette entries, only the
   default colors are available on the EGA, and their IDs don't correspond
   to those in 350-line mode (e.g. 20 is bright red, not brown). Attempting
   to set the palette with the data from the .PCX header will lead to odd
   results in these modes, and in any case should not be necessary.
*)

  for entry:= 0 to 15 do
  begin
    colorID:= 0;
    for gun:= 0 to 2 do
    begin
      pcxcode:= palbuf[16 + entry * 3 + gun];   { Get primary color value }
      if not is_VGA then
      begin                                     { Interpret for EGA }
        case (pcxcode div $40) of
          0: mask:= $00;    { 000000 }
          1: mask:= $20;    { 100000 }
          2: mask:= $04;    { 000100 }
          3: mask:= $24;    { 100100 }
        end;
        colorID:= colorID or (mask shr gun);    { Define two bits }
      end  { not is_VGA }
      else
      begin  { is_VGA }
        with RGBpal[entry] do                   { Interpret for VGA }
        case gun of
          0: redval:= pcxcode div 4;
          1: greenval:= pcxcode div 4;
          2: blueval:= pcxcode div 4;
        end;
      end;  { is_VGA }
    end;  { gun }
    if is_VGA then pal.colors[entry]:= entry
              else pal.colors[entry]:= colorID;
  end;  { entry }
  pal.size:= 16;
end;   { not is_CGA }

{ ---------------- Read and decode the image data ----------------------- }

repeatcount:= 0;                        { Initialize assembler vars. }
columncount:= 0;
repeat
  blockread(pcxfile, scratch^, buffsize, datalength);
  if is_CGA then decode_CGA else decode_16;   { Call assembler routine }
until eof(pcxfile);
close(pcxfile);
if not is_CGA then port[$3C5]:= $F;     { Reset mask map }
freemem(scratch,buffsize);              { Discard scratchpad }
end;  { READ_PCX_FILE }

{ ========================= 256-color files ============================= }

procedure DECODE_PCX256; assembler;

(* Registers used:

   AL   data byte to be written to video
   BX   end of input buffer
   CL   number of times data byte is to be written
   ES   output segment
   DI   index into output buffer
   DS   segment of input buffer
   SI   index into input buffer
*)

asm
mov     es, page_addr       { video segment }
mov     di, video_index     { index into video }
xor     cx, cx              { clean up loop counter }
mov     cl, repeatcount     { count in CL }
mov     bx, datalength      { end of input buffer }
push    ds                  { save DS }
lds     si, scratch         { pointer to input in DS:SI }
add     bx, si              { adjust datalength - SI may not be 0 }
cld                         { clear DF }
cmp     cl, 0               { was last byte a count? }
jne     @multi_data         { yes, so next is data }

{ --------------------- Loop through input buffer ----------------------- }

@getbyte:                   { last byte was not a count }
cmp     si, bx              { end of input buffer? }
je      @exit               { yes, quit }
lodsb                       { get byte into AL, increment SI }
cmp     al, 192             { test high bits }
jb      @one_data           { not set, not a count }
{ It's a count byte }
xor     al, 192             { get count from 6 low bits }
mov     cl, al              { store repeat count }
cmp     si, bx              { end of input buffer? }
je      @exit               { yes, quit }
@multi_data:
lodsb                       { get byte into AL, increment SI }
rep     stosb               { write byte CX times }
jmp     @getbyte
@one_data:
stosb                       { byte into video }
jmp     @getbyte

{ ------------------------- Finished with buffer ------------------------ }

@exit:
pop     ds                  { restore Turbo's data segment }
mov     video_index, di     { save status for next run thru buffer }
mov     repeatcount, cl
end;  { asm }

{ ================= Main procedure for 256-color files ================== }

procedure READ_PCX256(pfilename: pathstr);

var     x, gun, pcxcode: byte;
        pcxfile: file;
        palette_start, total_read: longint;
        palette_flag: byte;
        version: word;

procedure CLEANUP;

begin
close(pcxfile);
freemem(scratch, buffsize);
end;

begin    { READ_PCX256 }
assign(pcxfile, pfilename);
{$I-} reset(pcxfile, 1);  {$I+}
file_error:= (IOresult <> 0);
if file_error then exit;
getmem(scratch, buffsize);                  { Allocate scratchpad }
blockread(pcxfile, version, 2);             { Read first two bytes }
file_error:= (hi(version) < 5);             { No palette info. }
if file_error then
begin
  cleanup; exit;
end;
palette_start:= filesize(pcxfile) - 769;

seek(pcxfile, 128);                        { Scrap file header }
total_read:= 128;

repeatcount:= 0;                           { Initialize assembler vars. }
video_index:= 0;

repeat
  blockread(pcxfile, scratch^, buffsize, datalength);
  inc(total_read, datalength);
  if (total_read > palette_start) then
      dec(datalength, total_read - palette_start);
  decode_pcx256;
until (eof(pcxfile)) or (total_read>= palette_start);

(* The last 769 btes of the file are palette information, starting with a
   one-byte flag. Each group of three bytes represents the RGB values of
   one of the color registers. The values have to be divided by 4 to be
   brought within the range 0-63 expected by the registers. *)

seek(pcxfile, palette_start);
blockread(pcxfile, palette_flag, 1);
file_error:= (palette_flag <> 12);
if file_error then
begin
  cleanup; exit;
end;
blockread(pcxfile, RGB256, 768);         { Get palette info. }
for x:= 0 to 255 do
with RGB256[x] do
begin
  redval:= redval shr 2;
  greenval:= greenval shr 2;
  blueval:= blueval shr 2;
end;
cleanup;
end;  { READ_PCX256 }

{ ========================== Initialization ============================= }

BEGIN
page_addr:= page0;                      { Destination for EGA/VGA data }
END.