function SwapLong(const Value: Cardinal): Cardinal; asm BSWAP EAX//调用字节交换指令 end;
//抛出异常,参数为具体的异常信息 procedure RasError(const ErrorString: String); begin raise EInvalidGraphic.Create(ErrorString); end;
{下面是实现部分的代码。}
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)); //将文件头数据读取到记录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; //由于读取数据的顺序问题,这里需要调用上面的SwapLong改变顺序。 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)^); //当图像色深为8位,而又不存在调色板信息时,创建一个8位的灰度调色板 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)^); //读取文件中的调色板信息 //相关调色板操作的API请查询MSDN end else RasError('调色板长度错误!'); 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; //如果调色板长度不为0,而又未正确读取相关信息时,跳过这一段数据
case Header.Depth of 8: begin if Header.RasType = RT_BYTE_ENCODED then begin //ENCODE //关于RLE压缩的编码解码请自行查阅资料 RasError('不支持压缩格式!'); 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 //关于RLE压缩的编码解码请自行查阅资料 RasError('不支持压缩格式!'); 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; //当为RT_FORMAT_RGB格式时,按RGB获取数据,这里需要交换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位色时,需要调整读取后数据的顺序 end; end; RT_BYTE_ENCODED: begin //ENCODE //关于RLE压缩的编码解码请自行查阅资料 RasError('不支持压缩格式!'); 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; //这里将顺序调整和R和B值的交换的代码进行了合并 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;
{上面的代码中多次出现如下代码: if (Width mod 2)=1 then begin Position := Position + 1; end; 这是因为每行的数据都要按字对齐,既每行的数据都要用偶数的字节记录。当每个像素的颜色信息用1字节(8位)或3字节(24位)记录且每行像素数为奇数时,要补齐一个字节。所以这里跳过一个字节。 后面代码中的 if (Width mod 2) = 1 then begin FillByte:=0; Stream.Write(FillByte,1); end; 也是基于同一道理。}
procedure TRASGraphic.SaveToStream(Stream: TStream); var Header: TRASHeader; Row8: PByte; Row24: PRGBTriple; Row32: PRGBQuad; FillByte: Byte; Y: Integer; I: Integer; Pal: TMaxLogPalette; R,G,B:array[0..255] of Byte; begin Header.Magic := $956AA659; Header.Width := SwapLong(Width); Header.Height := SwapLong(Height); Header.RasType := SwapLong(RT_STANDARD); if (PixelFormat = pf1bit) or (PixelFormat = pf4bit) then PixelFormat:=pf8bit else if (PixelFormat <> pf8bit) and (PixelFormat <> pf24bit) and (PixelFormat <> pf32bit) then PixelFormat:=pf24bit; case PixelFormat of pf8bit: begin Header.Length := SwapLong(Height*(Width+(Width mod 2))); Header.Depth := SwapLong(8); Header.MapType := SwapLong(RMT_EQUAL_RGB); Header.MapLength := SwapLong(3*256); Stream.WriteBuffer(Header,SizeOf(Header)); GetPaletteEntries(Palette, 0, 256, Pal.palPalEntry); for I := 0 to 255 do begin R[I]:=Pal.palPalEntry[I].peRed; G[I]:=Pal.palPalEntry[I].peGreen; B[I]:=Pal.palPalEntry[I].peBlue; end; //相关调色板操作的API请查询MSDN Stream.WriteBuffer(R,256); Stream.WriteBuffer(G,256); Stream.WriteBuffer(B,256); for Y := 0 to Height-1 do begin Row8 := ScanLine[Y]; Stream.WriteBuffer(Row8^,Width); if (Width mod 2) = 1 then begin FillByte:=0; Stream.Write(FillByte,1); end; end; end; pf32bit: begin Header.Length := SwapLong(Height*Width*4); Header.Depth := SwapLong(32); Header.MapType := SwapLong(RMT_NONE); Header.MapLength := 0; Stream.WriteBuffer(Header,SizeOf(Header)); for Y := 0 to Height-1 do begin Row32 := ScanLine[Y]; for I := 0 to Width-1 do begin Stream.WriteBuffer(Row32.rgbReserved,1); Stream.WriteBuffer(Row32^,3); Inc(Row32); end; end; end; else begin Header.Length := SwapLong(Height*Width*3); Header.Depth := SwapLong(24); Header.MapType := SwapLong(RMT_NONE); Header.MapLength := 0; Stream.WriteBuffer(Header,SizeOf(Header)); for Y := 0 to Height-1 do begin Row24 := ScanLine[Y]; Stream.WriteBuffer(Row24^,Width*3); if (Width mod 2) = 1 then begin FillByte:=0; Stream.Write(FillByte,1); end; end; end; end; //SaveToStream基本上就是LoadFromStream的逆过程。