Mega Code Archive
Get width and height of a GIF image file
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Title: Get width and height of a GIF image file
function ReadMWord(f: TFileStream): Word;
type
TMotorolaWord = record
case Byte of
0: (Value: Word);
1: (Byte1, Byte2: Byte);
end;
var
MW: TMotorolaWord;
begin
f.read(MW.Byte2, SizeOf(Byte));
f.read(MW.Byte1, SizeOf(Byte));
Result := MW.Value;
end;
procedure GetGIFSize(const sGIFFile: string; var wWidth, wHeight: Word);
type
TGIFHeader = record
Sig: array[0..5] of char;
ScreenWidth, ScreenHeight: Word;
Flags, Background, Aspect: Byte;
end;
TGIFImageBlock = record
Left, Top, Width, Height: Word;
Flags: Byte;
end;
var
f: file;
Header: TGifHeader;
ImageBlock: TGifImageBlock;
nResult: integer;
x: integer;
c: char;
DimensionsFound: boolean;
begin
wWidth := 0;
wHeight := 0;
if sGifFile = '' then
Exit;
{$I-}
FileMode := 0; { read-only }
AssignFile(f, sGifFile);
reset(f, 1);
if IOResult 0 then
{ Could not open file }
Exit;
{ Read header and ensure valid file. }
BlockRead(f, Header, SizeOf(TGifHeader), nResult);
if (nResult SizeOf(TGifHeader)) or (IOResult 0) or
(StrLComp('GIF', Header.Sig, 3) 0) then
begin
{ Image file invalid }
Close(f);
Exit;
end;
{ Skip color map, if there is one }
if (Header.Flags and $80) 0 then
begin
x := 3 * (1 shl ((Header.Flags and 7) + 1));
Seek(f, x);
if IOResult 0 then
begin
{ Color map thrashed }
Close(f);
Exit;
end;
end;
DimensionsFound := False;
FillChar(ImageBlock, SizeOf(TGIFImageBlock), #0);
{ Step through blocks. }
BlockRead(f, c, 1, nResult);
while (not EOF(f)) and (not DimensionsFound) do
begin
case c of
',': { Found image }
begin
BlockRead(f, ImageBlock, SizeOf(TGIFImageBlock), nResult);
if nResult SizeOf(TGIFImageBlock) then
begin
{ Invalid image block encountered }
Close(f);
Exit;
end;
wWidth := ImageBlock.Width;
wHeight := ImageBlock.Height;
DimensionsFound := True;
end;
'?': { Skip }
begin
{ NOP }
end;
{ nothing else. just ignore }
end;
BlockRead(f, c, 1, nResult);
end;
Close(f);
{$I+}
end;
Example usage:
var width,height:word;
begin
GetGIFSize(filename,width, height);
end;
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