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{
fpImg - Free Pascal Imaging Library
Copyright (C) 2000 by
Areca Systems GmbH / Sebastian Guenther, sg@freepascal.org
Image reader for BMP files
See the file COPYING, included in this distribution,
for details about the copyright.
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
}
unit BMPReader;
{$IFDEF Debug}
{$ASSERTIONS On}
{$ENDIF}
interface
uses Classes, GFXBase, ImageIO;
type
DWORD = LongWord;
LONG = LongInt;
TBitmapFileHeader = packed record
bfType: WORD;
bfSize: DWORD;
bfReserved1: WORD;
bfReserved2: WORD;
bfOffBits: DWORD;
end;
TBitmapInfoHeader = packed record
biSize: DWORD;
biWidth: LONG;
biHeight: LONG;
biPlanes: WORD;
biBitCount: WORD;
biCompression: DWORD;
biSizeImage: DWORD;
biXPelsPerMeter: LONG;
biYPelsPerMeter: LONG;
biClrUsed: DWORD;
biClrImportant: DWORD;
end;
PRGBQuad = ^TRGBQuad;
TRGBQuad = packed record
rgbBlue, rgbGreen, rgbRed, rgbReserved: BYTE;
end;
TBMPReader = class(TImageReader)
protected
FFileHeader: TBitmapFileHeader;
FInfoHeader: TBitmapInfoHeader;
FBMPPalette: PRGBQuad;
FFileStride: LongWord;
HeaderBytesRead, PalBytesRead: Integer;
ScanlinesLeft: Integer;
ThisSegmentHeight: Integer;
ScanlinesLeftInSegment: Integer;
ScanlineBytesDone: LongWord;
CurScanline: Pointer;
procedure DoProcessHeaderData(AStream: TStream); override;
function DoGetImageSegmentStartY(ASegmentHeight: Integer): Integer;
override;
procedure InitImageReading; override;
procedure InitSegmentReading;
procedure DoProcessImageData(AStream: TStream); override;
public
destructor Destroy; override;
property FileHeader: TBitmapFileHeader read FFileHeader;
property InfoHeader: TBitmapInfoHeader read FInfoHeader;
property BMPPalette: PRGBQuad read FBMPPalette;
property FileStride: LongWord read FFileStride;
end;
implementation
destructor TBMPReader.Destroy;
begin
if Assigned(Palette) then
FreeMem(FPalette);
if Assigned(BMPPalette) then
FreeMem(FBMPPalette);
inherited Destroy;
end;
procedure TBMPReader.DoProcessHeaderData(AStream: TStream);
var
DataOffset: LongWord;
HaveRead, BytesToSkip, i: Integer;
IsFirstRead: Boolean;
SkipBuffer: array[0..1023] of Byte;
begin
if HeaderBytesRead < SizeOf(FileHeader) then
begin
HaveRead := AStream.Read(PChar(@FileHeader)[HeaderBytesRead],
SizeOf(FileHeader) - HeaderBytesRead);
if HaveRead = 0 then
raise EImgOutOfData.Create;
Inc(HeaderBytesRead, HaveRead);
IsFirstRead := False;
end else
IsFirstRead := True;
if HeaderBytesRead < SizeOf(FileHeader) + SizeOf(InfoHeader) then
begin
HaveRead := AStream.Read(
PChar(@InfoHeader)[HeaderBytesRead - SizeOf(FileHeader)],
SizeOf(FileHeader) + SizeOf(InfoHeader) - HeaderBytesRead);
if HaveRead = 0 then
if IsFirstRead then
raise EImgOutOfData.Create
else
exit;
IsFirstRead := False;
Inc(HeaderBytesRead, HaveRead);
end;
if HeaderBytesRead = SizeOf(FileHeader) + SizeOf(InfoHeader) then
begin
case InfoHeader.biBitCount of
1: FPaletteSize := 2;
4: FPaletteSize := 16;
8: FPaletteSize := 256;
end;
if PaletteSize > 0 then
begin
GetMem(FBMPPalette, PaletteSize * SizeOf(TRGBQuad));
GetMem(FPalette, PaletteSize * SizeOf(TGfxColor));
end;
end;
if HeaderBytesRead >= SizeOf(FileHeader) + SizeOf(InfoHeader) then
begin
DataOffset := FileHeader.bfOffBits;
if HeaderBytesRead < DataOffset then
begin
BytesToSkip := DataOffset - HeaderBytesRead;
if BytesToSkip > SizeOf(SkipBuffer) then
BytesToSkip := SizeOf(SkipBuffer);
HaveRead := AStream.Read(SkipBuffer, BytesToSkip);
if HaveRead = 0 then
if IsFirstRead then
raise EImgOutOfData.Create
else
exit;
IsFirstRead := False;
Inc(HeaderBytesRead, HaveRead);
if PalBytesRead < PaletteSize * SizeOf(TGfxPixel) then
begin
Move(SkipBuffer, PByte(FBMPPalette)[PalBytesRead], HaveRead);
Inc(PalBytesRead, HaveRead);
end;
end;
if HeaderBytesRead = DataOffset then
begin
FWidth := InfoHeader.biWidth;
FHeight := InfoHeader.biHeight;
if PaletteSize > 0 then
for i := 0 to PaletteSize - 1 do
begin
Palette[i].Red := BMPPalette[i].rgbRed * 257;
Palette[i].Green := BMPPalette[i].rgbGreen * 257;
Palette[i].Blue := BMPPalette[i].rgbBlue * 257;
Palette[i].Alpha := 0;
end;
case InfoHeader.biBitCount of
1:
begin
FFileStride := ((Width + 31) shr 3) and not 3;
FPixelFormat.FormatType := ftMono;
end;
4:
begin
FFileStride := ((Width + 7) shr 1) and not 3;
FPixelFormat.FormatType := ftPal4;
end;
8:
begin
FFileStride := (Width + 3) and not 3;
FPixelFormat.FormatType := ftPal8;
end;
24:
begin
FFileStride := (Width * 3 + 3) and not 3;
FPixelFormat := PixelFormatBGR24;
end;
else
raise EImgUnsupportedPixelFormat.Create;
end;
end;
HeaderFinished;
end;
end;
function TBMPReader.DoGetImageSegmentStartY(ASegmentHeight: Integer): Integer;
begin
Result := ScanlinesLeft - ASegmentHeight;
if Result < 0 then
Result := 0;
end;
procedure TBMPReader.InitImageReading;
begin
ScanlinesLeft := Height;
InitSegmentReading;
end;
procedure TBMPReader.InitSegmentReading;
begin
ThisSegmentHeight := ScanlinesLeft;
if ThisSegmentHeight > SegmentHeight then
ThisSegmentHeight := SegmentHeight;
ScanlinesLeftInSegment := ThisSegmentHeight;
ScanlineBytesDone := 0;
CurScanline := SegmentData + (ThisSegmentHeight - 1) * SegmentStride;
end;
procedure TBMPReader.DoProcessImageData(AStream: TStream);
procedure ScanlineDone;
begin
Dec(ScanlinesLeftInSegment);
Dec(ScanlinesLeft);
if ScanlinesLeftInSegment = 0 then
begin
SegmentFinished(ScanlinesLeft, ThisSegmentHeight);
if ScanlinesLeft = 0 then
ImageFinished
else
InitSegmentReading;
end else
Dec(CurScanline, SegmentStride);
end;
var
ReadMayFail: Boolean;
ToRead, HaveRead: Integer;
begin
if ScanlineBytesDone > 0 then
begin
ToRead := SegmentStride;
if ToRead > FileStride then
ToRead := FileStride;
Dec(ToRead, ScanlineBytesDone);
HaveRead := AStream.Read(PChar(CurScanline)[ScanlineBytesDone], ToRead);
if HaveRead = 0 then
raise EImgOutOfData.Create;
if HaveRead = ToRead then
begin
ScanlineBytesDone := 0;
ScanlineDone
end else
begin
Inc(ScanlineBytesDone, HaveRead);
exit;
end;
ReadMayFail := True;
end else
ReadMayFail := False;
while ScanlinesLeft > 0 do
begin
ToRead := SegmentStride;
if ToRead > FileStride then
ToRead := FileStride;
HaveRead := AStream.Read(CurScanline^, ToRead);
if HaveRead = 0 then
if ReadMayFail then
exit
else
raise EImgOutOfData.Create;
if HaveRead < ToRead then
begin
ScanlineBytesDone := HaveRead;
break;
end;
// Handle the ordinary case: a full scanline has been read
if ToRead < FileStride then
AStream.Position := AStream.Position + FileStride - ToRead;
ReadMayFail := True;
ScanlineDone;
end;
end;
end.
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