function GetGIFSize(const FileName: string): Types.TSize;
type
// GIF header record
TGIFHeader = packed record
Sig: array[0..5] of AnsiChar; // signature bytes
ScreenWidth, ScreenHeight: Word; // logical screen width and height
Flags: Byte; // various flags
Background: Byte; // background colour index
Aspect: Byte; // pixel aspect ratio
end;
// GIF image block header record
TGIFImageBlock = packed record
Left, Top: Word; // image top left
Width, Height: Word; // image dimensions
Flags: Byte; // flags and local colour table size
end;
const
cSignature: PAnsiChar = 'GIF'; // gif image signature
cImageSep = $2C; // image separator byte
var
FS: Classes.TFileStream; // stream onto gif file
Header: TGIFHeader; // gif header record
ImageBlock: TGIFImageBlock; // gif image block record
BytesRead: Integer; // bytes read in a block read
Offset: Integer; // file offset to seek to
B: Byte; // a byte read from gif file
DimensionsFound: Boolean; // flag true if gif dimensions have been read
begin
Result.cx := 0;
Result.cy := 0;
if (FileName = '') or not SysUtils.FileExists(FileName) then
Exit;
FS := Classes.TFileStream.Create(
FileName, SysUtils.fmOpenRead or SysUtils.fmShareDenyNone
);
try
// Check signature
BytesRead := FS.Read(Header, SizeOf(Header));
if (BytesRead <> SizeOf(TGIFHeader)) or
(SysUtils.StrLComp(cSignature, Header.Sig, 3) <> 0) then
// Invalid file format
Exit;
// Skip colour map, if there is one
if (Header.Flags and $80) > 0 then
begin
Offset := 3 * (1 shl ((Header.Flags and 7) + 1));
if Offset >= FS.Size then
Exit;
FS.Seek(Offset, Classes.soFromBeginning);
end;
DimensionsFound := False;
FillChar(ImageBlock, SizeOf(TGIFImageBlock), #0);
// Step through blocks
FS.Read(B, SizeOf(B));
while (FS.Position < FS.Size) and (not DimensionsFound) do
begin
if B = cImageSep then
begin
// We have an image block: read dimensions from it
BytesRead := FS.Read(ImageBlock, SizeOf(ImageBlock));
if BytesRead <> SizeOf(TGIFImageBlock) then
// Invalid image block encountered
Exit;
Result.cx := ImageBlock.Width;
Result.cy := ImageBlock.Height;
DimensionsFound := True;
end;
FS.Read(B, SizeOf(B));
end;
finally
FS.Free;
end;
end;
//delphi/2246