type
TRASGraphic = class(TBitmap)
public
procedure LoadFromStream(Stream: TStream); override;
procedure SaveToStream(Stream: TStream); override;
end;
//定義描述RAS文件頭的記錄類型
TRASHeader = packed record
Magic, //標(biāo)記
Width, //寬
Height, //高
Depth, //色深
Length, //圖像數(shù)據(jù)長度，可能會等于0
RasType, //格式類型
MapType, //調(diào)色板類型
MapLength: Cardinal; //調(diào)色板數(shù)據(jù)長度
end;
//定義一個用來描述RAS文件頭的記錄類型是非常必要的
const
//定義代表RAS所有類型的常量
RT_OLD = 0;
RT_STANDARD = 1;
RT_BYTE_ENCODED = 2;
RT_FORMAT_RGB = 3;
RT_FORMAT_TIFF = 4;
RT_FORMAT_IFF = 5;
RT_EXPERIMENTAL = $FFFF;
//定義代表調(diào)色板類型的常量
RMT_NONE = 0;//無調(diào)色板數(shù)據(jù)
RMT_EQUAL_RGB = 1;
RMT_RAW = 2;
{如果RAS的格式為RT_OLD，數(shù)據(jù)長度可能為0}
function SwapLong(const Value: Cardinal): Cardinal;
asm
BSWAP EAX//調(diào)用字節(jié)交換指令
end;
//拋出異常，參數(shù)為具體的異常信息
procedure RasError(const ErrorString: String);
begin
raise EInvalidGraphic.Create(ErrorString);
end;
{下面是實現(xiàn)部分的代碼。}
procedure TRASGraphic.LoadFromStream(Stream: TStream);
var
Header: TRASHeader;
Row8: PByte;
Row24: PRGBTriple;
Row32: PRGBQuad;
PMap: PByte;
Y: Integer;
I: Integer;
MapReaded: Boolean;
Pal: TMaxLogPalette;
R,G,B:array[0..255] of Byte;
ColorByte: Byte;
begin
with Stream do
begin
ReadBuffer(Header, SizeOf(Header)); //將文件頭數(shù)據(jù)讀取到記錄Header中
with Header do
begin
Width := SwapLong(Width);
Height := SwapLong(Height);
Depth := SwapLong(Depth);
Length := SwapLong(Length);
RASType := SwapLong(RASType);
MapType := SwapLong(MapType);
MapLength := SwapLong(MapLength);
end;
//由于讀取數(shù)據(jù)的順序問題，這里需要調(diào)用上面的SwapLong改動順序。
if (Header.Magic = $956AA659) and
(Header.Width<>0) and (Header.Height<>0) and
(Header.Depth in [1,8,24,32]) and (Header.RasType in [RT_OLD,RT_STANDARD,RT_BYTE_ENCODED,RT_FORMAT_RGB]) then
begin
Width := Header.Width;
Height := Header.Height;
MapReaded := False;
case Header.Depth of
1:PixelFormat := pf1Bit;
8:
begin
PixelFormat := pf8Bit;
case Header.MapType of
RMT_NONE:
begin
Pal.palVersion:=$300;
Pal.palNumEntries:=256;
for I := 0 to 255 do
begin
Pal.palPalEntry[I].peRed:=I;
Pal.palPalEntry[I].peGreen:=I;
Pal.palPalEntry[I].peBlue:=I;
Pal.palPalEntry[I].peFlags:=0;
end;
Palette := CreatePalette(PLogPalette(@Pal)^);
//當(dāng)圖像色深為8位，而又不存在調(diào)色板信息時，創(chuàng)建一個8位的灰度調(diào)色板
end;
RMT_EQUAL_RGB:
begin
if (Header.MapLength = 3*256) then
begin
Pal.palVersion:=$300;
Pal.palNumEntries:=256;
ReadBuffer(R,256);
ReadBuffer(G,256);
ReadBuffer(B,256);
for I := 0 to 255 do
begin
Pal.palPalEntry[I].peRed:=R[I];
Pal.palPalEntry[I].peGreen:=G[I];
Pal.palPalEntry[I].peBlue:=B[I];
Pal.palPalEntry[I].peFlags:=0;
end;
Palette := CreatePalette(PLogPalette(@Pal)^);
//讀取文件中的調(diào)色板信息
//相關(guān)調(diào)色板操作的API請查詢MSDN
end
else
RasError(調(diào)色板長度錯誤！);
MapReaded := True;
end;
RMT_RAW:
begin
RasError(不支持的文件格式！);
end;
end;
end;
24:PixelFormat := pf24Bit;
32:
begin
PixelFormat := pf32Bit;
//
end;
end;
if (not MapReaded) and (Header.MapLength>0) then
begin
Position := Position + Header.MapLength;
end;
//如果調(diào)色板長度不為0，而又未正確讀取相關(guān)信息時，跳過這一段數(shù)據(jù)
case Header.Depth of
8:
begin
if Header.RasType = RT_BYTE_ENCODED then
begin
//ENCODE
//關(guān)于RLE壓縮的編碼解碼請自行查閱資料
RasError(不支持壓縮格式！);
end
else
begin
for Y := 0 to Height-1 do
begin
Row8:=ScanLine[Y];
ReadBuffer(Row8^,Width);
if (Width mod 2)=1 then
begin
Position := Position + 1;
end;
end;
end;
end;{end of 8Bit}
24:
begin
case Header.RasType of
RT_OLD,
RT_STANDARD:
begin
for Y := 0 to Height-1 do
begin
Row24:=ScanLine[Y];
ReadBuffer(Row24^,Width*3);
if (Width mod 2)=1 then
begin
Position := Position + 1;
end;
end;
end;
RT_BYTE_ENCODED:
begin
//ENCODE
//關(guān)于RLE壓縮的編碼解碼請自行查閱資料
RasError(不支持壓縮格式！);
end;
RT_FORMAT_RGB:
begin
for Y := 0 to Height-1 do
begin
Row24:=ScanLine[Y];
ReadBuffer(Row24^,Width*3);
for I := 0 to Width-1 do
begin
ColorByte := Row24^.rgbtRed;
Row24^.rgbtRed := Row24^.rgbtBlue;
Row24^.rgbtBlue := ColorByte;
Inc(Row24);
end;
//當(dāng)為RT_FORMAT_RGB格式時，按RGB獲取數(shù)據(jù)，這里需要交換R和B的值
if (Width mod 2)=1 then
begin
Position := Position + 1;
end;
end;
end;{end of RT_FORMAT_RGB}
else
RasError(不支持的文件格式！);
end;
end;{end of 24Bit}
32:
begin
case Header.RasType of
RT_OLD,
RT_STANDARD:
begin
for Y := 0 to Height-1 do
begin
Row32:=ScanLine[Y];
ReadBuffer(Row32^,Width*4);
for I := 0 to Width-1 do
begin
ColorByte := Row32^.rgbReserved;
Row32^.rgbReserved := Row32^.rgbBlue;
Row32^.rgbBlue := Row32^.rgbGreen;
Row32^.rgbGreen := Row32^.rgbRed;
Row32^.rgbRed := ColorByte;
Inc(Row32);
end;
//32位色時，需要調(diào)整讀取后數(shù)據(jù)的順序
end;
end;
RT_BYTE_ENCODED:
begin
//ENCODE
//關(guān)于RLE壓縮的編碼解碼請自行查閱資料
RasError(不支持壓縮格式！);
end;
RT_FORMAT_RGB:
begin
For Y := 0 to Height-1 do
begin
Row32:=ScanLine[Y];
ReadBuffer(Row32^,Width*4);
for I := 0 to Width-1 do
begin
ColorByte := Row32^.rgbBlue;
Row32^.rgbBlue := Row32^.rgbReserved;
Row32^.rgbReserved := ColorByte;
ColorByte := Row32^.rgbGreen;
Row32^.rgbGreen := Row32^.rgbRed;
Row32^.rgbRed := ColorByte;
Inc(Row32);
end;
//這里將順序調(diào)整和R和B值的交換的代碼進(jìn)行了合并
end;
end;{end of RT_FORMAT_RGB}
else
RasError(不支持的文件格式！);
end;{end of 32Bit}
end;
else
begin
FreeImage;
RasError(不支持的文件格式！);
end;
end;
end
else
RasError(不支持的文件格式！);
end;{end with}
end;
{上面的代碼中多次出現(xiàn)如下代碼：
if (Width mod 2)=1 then
begin
Position := Position + 1;
end;
