{ Caveats:
1. This ONLY converts 256 color bitmaps!
2. The only format supported is GIF87a.
}
unit Bmp2Gif;
interface
uses
SysUtils,
Classes,
Windows,
Graphics;
function SaveAsGif(InputBM : TBitmap; FName : string) : boolean;
implementation
const
BlockTerminator:byte = 0;
FileTrailer:byte = $3B;
gifBGColor:byte = 0;
gifPixAsp:byte = 0;
gifcolordepth:byte = 8; // 8 bit = 256 colors
gifncolors:integer = 256;
gifLIDid:byte = $2C;
HASHSIZE:integer = 5101;
HASHBITS:integer = 4;
TABLSIZE:integer = 4096;
EMPTY:integer = -1;
var
F : integer;
Dbg : TextFile;
MapBM : TBitmap;
ImageWidth,ImageHeight:Integer;
buffer : array[0..255] of byte;
codes : array[0..5101] of Integer;
prefix: array[0..5101] of Integer;
suffix: array[0..5101] of Integer;
nBytes,nbits, size,cursize, curcode, maxcode : Integer;
BitmapSizeImage : Integer;
Started : Boolean;
minsize,maxsize,nroots,Capacity : Integer;
endc, clrc : Integer;
MinLZWCodeSize : Byte;
bytecode,bytemask :Integer;
counter : Integer;
strc,chrc :Integer;
ErrorMsg : string;
function Putbyte(B,fh:Integer):Boolean;
begin
Counter := counter + 1;
buffer[nbytes] := B;
Inc(nbytes);
If nbytes = 255 then
begin
//ShowMessage('255');
FileWrite(fh,nbytes,1);
FileWrite(fh,buffer,nbytes);
nbytes := 0;
end;
result := True;
end;
function PutCode(code, fh :Integer) : Boolean;
var
temp,n,mask :Integer;
begin
mask := 1;
n := nbits;
//If nbits > 11 then ShowMessage('nbits = 12');
while n > 0 do
begin
dec(n);
if ((code and mask)<>0) then bytecode := (bytecode or bytemask);
bytemask := bytemask shl 1;
if (bytemask > $80) then
begin
If PutByte(bytecode,fh) then
begin
bytecode := 0;
bytemask := 1;
end;
end;
mask := mask shl 1;
end;
result := True;
end;
procedure Flush(fh:Integer);
begin
if bytemask <> 1 then
begin
PutByte(byteCode,fh);
bytecode :=0;
bytemask :=1;
end;
if nbytes > 0 then
begin
FileWrite(fh,nbytes,1);
FileWrite(fh,buffer,nbytes);
nbytes :=0;
end;
end;
procedure ClearX;
var
J : Integer;
begin
cursize := minsize;
nbits := cursize;
curcode := endc + 1;
maxcode := 1 shl cursize;
for J := 0 to HASHSIZE do codes[J] := EMPTY;
end;
function findstr(pfx,sfx :Integer):integer;
var
i,di : Integer;
begin
i := (sfx shl HASHBITS) xor pfx;
if i = 0 then di := 1 else di := Capacity -i;
while True do
begin
if codes[i] = EMPTY then break;
if ((prefix[i] = pfx) and (suffix[i] = sfx)) then break;
i := i - di;
if i < 0 then i := i + Capacity;
end;
Result := i;
end;
procedure EncodeScanLine(fh : Integer; var buf : Pbyte; npxls : Integer);
var
np,I : Integer;
begin
np := 0;
if not Started then
begin
strc := buf^;
Inc(np); Inc(buf);
Started := True;
end;
while np < npxls do
begin
// If np = 3 then break;
chrc := buf^;
Inc(np); Inc(buf);
I := findstr(strc,chrc);
if codes[I] <> EMPTY then
strc := codes[I]
else
begin
codes[I] := curcode;
prefix[I] := strc;
suffix[I] := chrc;
putcode(strc,fh);
strc := chrc;
Inc(curcode);
if curcode > maxcode then
begin
Inc(cursize);
if cursize > maxsize then
begin
putcode(clrc,fh);
ClearX;
end
else
begin
nbits := cursize;
maxcode := maxcode shl 1;
if cursize = maxsize then dec(maxcode);
end;
end;
end;
end;
end;
procedure Initialize(fh:integer);
var
flags : Byte;
begin
counter := 0;
Started := False;
size := 8;
nbytes := 0;
nbits := 8;
bytecode := 0;
bytemask := 1;
Capacity := HASHSIZE;
minsize := 9;
maxsize := 12;
nroots := 1 shl 8;
clrc := nroots;
endc := clrc + 1;
MinLZWCodeSize := 8;
ClearX;
// Write the type
FileWrite(fh,'GIF87a',6);
// Write the GIF screen descriptor
// Note: width > 255 is a two byte word!!
FileWrite(fh,ImageWidth,2);
FileWrite(fh,ImageHeight,2);
flags := $80 or ((gifcolordepth-1)shl 4) or (gifcolordepth-1);
FileWrite(fh,flags,1);
FileWrite(fh,gifBGColor,1);
FileWrite(fh,gifPixAsp,1);
end;
procedure WriteGif(fh : integer);
var
F:TextFile;
gifxLeft,gifyTop : word; //Must be 16 bit!!
flags :Byte;
K : Pointer;
Test,J,M : Integer;
scanLine, TempscanLine, Bits, PBits : PByte;
begin
//Get the info from the Bitmap
GetMem(K,(sizeof(TBitMapInfoHeader) + 4 * gifncolors));
TBitmapInfo(K^).bmiHeader.biSize := sizeof(TBitMapInfoHeader);
TBitmapInfo(K^).bmiHeader.biWidth := ImageWidth;
TBitmapInfo(K^).bmiHeader.biHeight := ImageHeight;
TBitmapInfo(K^).bmiHeader.biPlanes := 1;
TBitmapInfo(K^).bmiHeader.biBitCount := 8;
TBitmapInfo(K^).bmiHeader.biCompression := BI_RGB;
TBitmapInfo(K^).bmiHeader.biSizeImage :=
((((TBitmapInfo(K^).bmiHeader.biWidth * TBitmapInfo(K^).bmiHeader.biBitCount)+31)
and Not(31)) shr 3)*TBitmapInfo(K^).bmiHeader.biHeight;
TBitmapInfo(K^).bmiHeader.biXPelsPerMeter := 0;
TBitmapInfo(K^).bmiHeader.biYPelsPerMeter := 0;
TBitmapInfo(K^).bmiHeader.biClrUsed := 0;
TBitmapInfo(K^).bmiHeader.biClrImportant := 0;
try
GetMem(Bits,TBitmapInfo(K^).bmiHeader.biSizeImage);
Test := GetDIBits(MapBM.Canvas.Handle,MapBM.Handle,0,ImageHeight,Bits,TBitmapInfo(K^),DIB_RGB_COLORS);
If Test > 0 then
begin
for J := 0 to 255 do
begin
FileWrite(fh,TBitMapInfo(K^).bmiColors[J].rgbRed,1);
FileWrite(fh,TBitMapInfo(K^).bmiColors[J].rgbGreen,1);
FileWrite(fh,TBitMapInfo(K^).bmiColors[J].rgbBlue,1);
end;
//Write the Logical Image Descriptor
FileWrite(fh,gifLIDid,1);
gifxLeft := 0; FileWrite(fh,gifxLeft,2); // Write X position of image
gifyTop := 0; FileWrite(fh,gifyTop,2); // Write Y position of image
FileWrite(fh,ImageWidth,2);
FileWrite(fh,ImageHeight,2);
flags := 0; FileWrite(fh,flags,1); //Write Local flags 0=None
//Write Min LZW code size = 8 (for 8 bit)
MinLZWCodeSize := 8;
FileWrite(fh,MinLZWCodesize,1);
PutCode(clrc,fh);
PBits := Bits;
Inc(Pbits,(ImageWidth *(ImageHeight -1)));
GetMem(scanLine,ImageWidth);
TempscanLine := scanLine;
For M := 0 to ImageHeight-1 do
begin
FillChar(scanLine^,ImageWidth,0);
move(PBits^,scanLine^,ImageWidth);
EncodeScanLine(fh,scanLine,ImageWidth);
dec(scanLine,ImageWidth);
Dec(PBits,ImageWidth);
end;
end;
finally
scanLine := TempscanLine;
FreeMem(scanLine,ImageWidth);
FreeMem(Bits,TBitMapInfo(K^).bmiHeader.biSizeImage);
FreeMem(K,(sizeof(TBitMapInfoHeader) + 4 * gifncolors));
end;
end;
function SaveAsGif(InputBM : TBitmap; FName : string) : boolean;
begin
ErrorMsg := '';
Result := FALSE;
MapBM := InputBM;
ImageWidth := MapBM.Width;
ImageHeight := MapBM.Height;
F := FileCreate(FName);
if F >= 0 then
begin
Initialize(F);
WriteGif(F);
PutCode(strc,F);
PutCode(endc,F);
Flush(F);
FileWrite(F,BlockTerminator,1);
FileWrite(F,FileTrailer,1);
FileClose(F);
if length(ErrorMsg) = 0 then Result := TRUE;
end;
end;
end.