BMP

2011-01-14T16:46:23Z

SamSam: New page: In this article we will focus on the Flight Simulator flavored version of BMP used for textures, an extension of the BMP or Bitmap File Format, a well known image format mainly used on Mic...

In this article we will focus on the Flight Simulator flavored version of BMP used for textures, an extension of the BMP or Bitmap File Format, a well known image format mainly used on Microsoft Windows operating systems. These files are usually generated with ImageTool that comes with the SDK.

There are two differences with a standard BMP :
* the header have an "FS70" extension;
* the pixels may be stored in various [[DXT]] format.

== Standard Header Structure ==

Here is the equivalent C++ structure of the header. It start with magic signature :

struct BITMAPMAGIC {
BYTE Magic[2]; //Magic is always {'B', 'M'}
};

It is immedialty followed (without padding) by the file header :

struct BITMAPFILEHEADER {
DWORD Size; //The total size of the file
WORD Creator1; //Application depend
WORD Creator2; //Application depend
DWORD Offset; //Offset tot eh pixel data
};

Then follows the bitmap infos :

struct BITMAPINFO {
BITMAPINFOHEADER Header;
RGBQUAD Colors[1];
}

where BITMAPINFOHEADER is :

struct BITMAPINFOHEADER {
DWORD Size; //The size of this header (40)
LONG Width; //The width of the image in pixel
LONG Height; //The height of the image in pixel
WORD Planes; //The number of planes (1)
WORD BitCount; //The number of bits-per-pixel
DWORD Compression; //The type of compression
DWORD SizeImage; //The size of the image in bytes
LONG XPelsPerMeter; //The horizontal resolution
LONG YPelsPerMeter; //The vertical resolution
DWORD ClrUsed; //The number of color indexes actually used
DWORD ClrImportant; //The number of color indexes required
};

and RGBQUAD is

struct RGBQUAD {
BYTE Blue;
BYTE Green;
BYTE Red;
BYTE Reserved;
};

and contains a possible palette. So far, we are on familiar ground. For more details you may found the following links usefull :

[[http://msdn.microsoft.com/en-us/library/dd183377 MSDN]]
[[http://en.wikipedia.org/wiki/BMP_file_format WikiPedia]]

== FSX Header Structure ==

After the standard header a FS70 extension is found :

struct BITMAPFSXHEADER {
BYTE Format[4]; //Format is always {'F', 'S', '7', '0'}.
DWORD Version; //Version is always 20
BYTE Reserved;
BYTE Alpha; //Set to 1 if the BMP has an alpha layer
BYTE Reserved;
BYTE Reserved;
BYTE HasBorder; //Set to 1 is the BMP has a 1 pixel border
WORD NbMips; //The number of mips
DWORD Reserved;
};

Some of the Reserved fields may have meanings that are not discovered yet.

== Pixel Data ==

Right after the FS70 header the pixel section stored uncompressed (packed in rows) or in compressed format.

For an uncompressed format the expected size of this section is ImageHeight * ImageWidth * BitsPerPixel / 32 * 4.

[[category:File Formats]]
[[category:FSX]]

FSDeveloper Wiki - User contributions [en-gb]

BMP