avoid an unneeded check in the FT1 has_chars() method implementation

[imager.git] / fileformatdocs / bmp.txt

BITMAPFILEHEADER  [3.0]

Bitmap File Information
The BITMAPFILEHEADER data structure contains information about the type, 
size, and layout of a device-independent bitmap (DIB) file.

typedef struct tagBITMAPFILEHEADER {
        WORD    bfType;
        DWORD   bfSize;
        WORD    bfReserved1;
        WORD    bfReserved2;
        DWORD   bfOffBits;
} BITMAPFILEHEADER;

The BITMAPFILEHEADER data structure contains the following fields:

Field		Description
bfType		Specifies the type of file. It must be BM.
bfSize		Specifies the size in DWORDs of the file. 
bfReserved1	Is reserved and must be set to zero. 
bfReserved2	Is reserved and must be set to zero. 
bfOffBits	Specifies in bytes the offset from the BITMAPFILEHEADER 
		of the actual bitmap in the file. 

Comments	A BITMAPINFO or BITMAPCOREINFO data structure immediately 
follows the BITMAPFILEHEADER structure in the DIB file.


BITMAPINFO  [3.0]

Device-Indpendent Bitmap Information
The BITMAPINFO structure fully defines the dimensions and color 
information for a Windows 3.0 device-independent bitmap.

typedef struct tagBITMAPINFO { 
   BITMAPINFOHEADER    bmiHeader;
   RGBQUAD             bmiColors[1];
} BITMAPINFO;

The BITMAPINFO structure contains the following fields:

Field	Description
bmiHeader	Specifies a BITMAPINFOHEADER data structure that 
		contains information about the dimensions and color 				format of a device-independent bitmap. 
bmiColors	Specifies an array of RGBQUAD data structures that 
		define the colors in the bitmap.  

Comments:	A Windows 3.0 device-independent bitmap consists of two 
distinct parts: a BITMAPINFO data structure that describes the dimensions 
and colors of the bitmap, and an array of bytes that define the pixels of 
the bitmap. The bits in the array are packed together, but each scan line 
must be zero-padded to end on a LONG boundary. Segment boundaries can 
appear anywhere in the bitmap, however. The origin of the bitmap is the 
lower-left corner.

The biBitCount field of the BITMAPINFOHEADER structure determines the 
number of bits which define each pixel and the maximum number of colors 
in the bitmap. This field may be set to any of the following values:

Value	Meaning
1	The bitmap is monochrome, and the bmiColors field must 
	contain two entries. Each bit in the bitmap array represents a 
	pixel. If the bit is clear, the pixel is displayed with the
 	color of the first entry in the bmiColors table; if the bit is
 	set, the pixel has the color of the second entry in the table.
4	The bitmap has a maximum of 16 colors, and the bmiColors 
	field contains up to 16 entries. Each pixel in the bitmap is 
	represented by a four-bit index into the color table.
	For example, if the first byte in the bitmap is 0x1F,  then the 
	byte represents two pixels. The first pixel contains the color 
	in the second table entry, and the second pixel contains the 
	color in the 16th table entry.
8	The bitmap has a maximum of 256 colors, and the bmiColors 
	field contains up to 256 entries. In this case, each byte in the 
	array represents a single pixel.
24	The bitmap has a maximum of 2^24 colors. The bmiColors 
	field is NULL, and each three bytes in the bitmap array 
	represents the relative intensities of red, green, and blue, 
	respectively, of a pixel.

The biClrUsed field of the BITMAPINFOHEADER structure specifies the number
of color indexes in the color table actually used by the bitmap. If the 
biClrUsed field is set to 0, the bitmap uses the maximum number of colors 
corresponding to the value of the biBitCount field.

The colors in the bmiColors table should appear in order of importance.

Alternatively, for functions that use device-independent bitmaps, the 
bmiColors field can be an array of 16-bit unsigned integers that specify 
an index into the currently realized logical palette instead of explicit 
RGB values. In this case, an application using the bitmap must call 
device-independent bitmap functions with the wUsage parameter set to 
DIB_PAL_COLORS.

Note:	The bmiColors field should not contain palette indices if the 
bitmap is to be stored in a file or transferred to another application. 
Unless the application uses the bitmap exclusively and under its complete 
control, the bitmap color table should contain explicit RGB values.

BITMAPINFOHEADER  [3.0]

Device-Independent Bitmap Format Information
The BITMAPINFOHEADER structure contains information about the dimensions 
and color format of a Windows 3.0 device-independent bitmap.

typedef struct tagBITMAPINFOHEADER{
   DWORD  biSize;
   DWORD  biWidth;
   DWORD  biHeight;
   WORD   biPlanes;
   WORD   biBitCount
   DWORD  biCompression;
   DWORD  biSizeImage;
   DWORD  biXPelsPerMeter;
   DWORD  biYPelsPerMeter;
   DWORD  biClrUsed;
   DWORD  biClrImportant;
} BITMAPINFOHEADER;

The BITMAPINFOHEADER structure has the following fields:

Field		Description
biSize		Specifies the number of bytes required by the 
		BITMAPINFOHEADER structure. 
biWidth		Specifies the width of the bitmap in pixels. 
biHeight	Specifies the height of the bitmap in pixels. 
biPlanes	Specifies the number of planes for the target device and
 		must be set to 1. 
biBitCount	Specifies the number of bits per pixel. This value must 
		be 1, 4, 8, or 24. 
biCompression	Specifies the type of compression for a compressed 	
		bitmap. It can be one of the following values:.
		Value		Meaning
		BI_RGB		Specifies that the bitmap is not 
				compressed.
		BI_RLE8		Specifies a run-length encoded format 
				for bitmaps with 8 bits per pixel. The 
				compression format is a two-byte 
				format consisting of a count byte 
				followed by a byte containing a color 
				index. See the following 'Comments' 
				section for more information.
		BI_RLE4		Specifies a run-length encoded format 
				for bitmaps with 4 bits per pixel. The 
				compression format is a two-byte 
				format consisting of a count byte 
				followed by two word-length color 
				indexes. See the following 'Comments' 
				section for more information.
biSizeImage	Specifies the size in bytes of the image. 
biXPelsPerMeter	Specifies the horizontal resolution in pixels per meter 			of the target device for the bitmap. An application can 			use this value to select a bitmap from a resource group 			that best matches the characteristics of the current 				device. biYPelsPerMeter	Specifies the vertical 					resolution in pixels per meter of the target device for 			the bitmap. 
biClrUsed	Specifies the number of color indexes in the color table 
		actually used by the bitmap. If this value is 0, the 	
		bitmap uses the maximum number of colors corresponding 	
		to the value of the biBitCount field. See the 		
		description of the BITMAPINFO data structure earlier in 	
		this chapter for more information on the maximum sizes 
		of the color table. If biClrUsed is nonzero, then the 
		biClrUsed field specifies the actual number of colors 
		which the graphics engine or device driver will access 
		if the biBitCount field is less than 24. If the 	
		biBitCount field is set to 24, the biClrUsed field 	
		specifies the size of the reference color table used to 
		optimize performance of Windows color palettes.
		If the bitmap is a 'packed' bitmap (that is, a bitmap in 
		which the bitmap array immediately follows the 	
		BITMAPINFO header and which is referenced by a single 	
		pointer), the biClrUsed field must be set to 0 or to the 
		actual size of the color table. 
biClrImportant	Specifies the number of color indexes that are considered 
		important for displaying the bitmap. If this value is 0, 	
		then all colors are important. 

Comments:	The BITMAPINFO data structure combines the 
BITMAPINFOHEADER structure and a color table to provide a complete 
definition of the dimensions and colors of a Windows 3.0 
device-independent bitmap. See the description of the BITMAPINFO data 
structure for more information about specifying a Windows 3.0 
device-independent bitmap.

An application should use the information stored in the biSize field to 
locate the color table in a BITMAPINFO data structure with a method such 
as the following:

pColor = ((LPSTR) pBitmapInfo + (WORD) (pBitmapInfo -> biSize))

Bitmap Compression Formats	Windows supports formats for compressing 
bitmaps that define their colors with 8 bits per pixel and with 4 bits 
per pixel. Compression reduces the disk and memory storage required for 
the bitmap. The following paragraphs describe these formats.

When the biCompression field is set to BI_RLE8, the bitmap is compressed 
using a run-length encoding format for an 8-bit bitmap. This format may 
be compressed in either of two modes:

7	Encoded
7	Absolute


Both modes can occur anywhere throughout a single bitmap.

Encoded mode consists of two bytes:  the first byte specifies the number 
of consecutive pixels to be drawn using the color index contained in the 
second byte. In addition, the first byte of the pair can be set to zero 
to indicate an escape that denotes an end of line, end of bitmap, or a 
delta. The interpretation of the escape depends on the value of the 
second byte of the pair. The following list shows the meaning of the 
second byte:

Second Byte
Of Escape	
		Meaning
0		End of line.
1		End of bitmap.
2		Delta. The two bytes following the escape contain
 		unsigned values indicating the horizontal and vertical
 		offset of the next pixel from the current position.

Absolute mode is signalled by the first byte set to zero and the second 
byte set to a value between 03H and FFH. In absolute mode, the second 
byte represents the number of bytes which follow, each of which contains
the color index of a single pixel. When the second byte is set to 2 or 
less, the escape has the same meaning as in encoded mode. 
In absolute mode, each run must be aligned on a word boundary.

The following example shows the hexadecimal values of an 8-bit compressed 
bitmap:

03 04 05 06 00 03 45 56 67 00 02 78 00 02 05 01 
02 78 00 00 09 1E 00 01

This bitmap would expand as follows (two-digit values represent a color 
index for a single pixel):

04 04 04
06 06 06 06 06
45 56 67
78 78
move current position 5 right and 1 down
78 78
end of line
1E 1E 1E 1E 1E 1E 1E 1E 1E 
end of RLE bitmap

When the biCompression field is set to BI_RLE4, the bitmap is compressed 
using a run-length encoding format for a 4-bit bitmap, which also uses 
encoded and absolute modes. In encoded mode, the first byte of the pair 
contains the number of pixels to be drawn using the color indexes in the 
second byte. The second byte contains two color indexes, one in its 
high-order nibble (that is, its low-order four bits) and one in its 
low-order nibble. The first of the pixels is drawn using the color 
specified by the high-order nibble, the second is drawn using the color 
in the low-order nibble, the third is drawn with the color in the 
high-order nibble, and so on, until all the pixels specified by the 
first byte have been drawn.

In absolute mode, the first byte contains zero, the second byte contains 
the number of color indexes that follow, and subsequent bytes contain 
color indexes in their high- and low-order nibbles, one color index for 
each pixel. In absolute mode, each run must be aligned on a word boundary.
The end-of-line, end-of-bitmap, and delta escapes also apply to BI_RLE4.

The following example shows the hexadecimal values of a 4-bit compressed 
bitmap:

03 04 05 06 00 06 45 56 67 00 04 78 00 02 05 01 
04 78 00 00 09 1E 00 01

This bitmap would expand as follows (single-digit values represent a 
color index for a single pixel):

0 4 0
0 6 0 6 0 
4 5 5 6 6 7
7 8 7 8
move current position 5 right and 1 down
7 8 7 8
end of line
1 E 1 E 1 E 1 E 1
end of RLE bitmap

RGBQUAD  [3.0]

RGB Color Structure
The RGBQUAD data structure describes a color consisting of relative 
intensities of red, green, and blue. The bmiColors field of the 
BITMAPINFO data structure consists of an array of RGBQUAD data structures.

typedef struct tagRGBQUAD {
   BYTE    rgbBlue;
   BYTE    rgbGreen;
   BYTE    rgbRed;
   BYTE    rgbReserved;
} RGBQUAD;

The RGBQUAD structure contains the following fields:

Field		Description
rgbBlue		Specifies the intensity of blue in the color. 
rgbGreen	Specifies the intensity of green in the color. 
rgbRed		Specifies the intensity of red in the color. 
rgbReserved	Is not used and must be set to zero. 



#define BI_RGB      0L
#define BI_RLE8     1L
#define BI_RLE4     2L

BITMAPCOREINFO  [3.0]

Device-Indpendent Bitmap Information
The BITMAPCOREINFO structure fully defines the dimensions and color 
information for a device-independent bitmap that is compatible with 
Microsoft OS/2 Presentation Manager versions 1.1 and 1.2 bitmaps.

typedef struct _BITMAPCOREINFO {
        BITMAPCOREHEADER  bmciHeader;
        RGBTRIPLE         bmciColors[];
} BITMAPCOREINFO;

The BITMAPCOREINFO structure contains the following fields:

Field	Description
bmciHeader	Specifies a BITMAPCOREHEADER data structure that 
		contains information about the dimensions and color 
		format of a device-independent bitmap. 
bmciColors	Specifies an array of RGBTRIPLE data structures that 
		define the colors in the bitmap.  

Comments	An OS/2 Presentation Manager device-independent bitmap 
consists of two distinct parts:  a BITMAPCOREINFO data structure that 
describes the dimensions and colors of the bitmap, and an array of bytes 
which define the pixels of the bitmap. The bits in the array are packed 
together, but each scan line must be zero-padded to end on a LONG 
boundary. Segment boundaries can appear anywhere in the bitmap, however. 
The origin of the bitmap is the lower-left corner.

The bcBitCount field of the BITMAPCOREHEADER structure determines the 
number of bits which define each pixel and the maximum number of colors 
in the bitmap. This field may be set to any of the following values:

Value	Meaning
1	The bitmap is monochrome, and the bmciColors field must 
	contain two entries. Each bit in the bitmap array represents a 
	pixel. If the bit is clear, the pixel is displayed with the 
	color of the first entry in the bmciColors table; if the bit is 
	set, the pixel has the color of the second entry in the table.
4	The bitmap has a maximum of 16 colors, and the bmciColors 
	field contains 16 entries. Each pixel in the bitmap is represented 
	by a four-bit index into the color table.
	For example, if the first byte in the bitmap is 0x1F,  then the 
	byte represents two pixels. The first pixel contains the color in 
	the second table entry, and the second pixel contains the color 
	in the 16th table entry.
8	The bitmap has a maximum of 256 colors, and the bmciColors 
	field contains 256 entries. In this case, each byte in the array 
	represents a single pixel.
24	The bitmap has a maximum of 2^24 colors. The bmciColors 
	field is NULL, and each three bytes in the bitmap array 
	represents the relative intensities of red, green, and blue, 
	respectively, of a pixel.

The colors in the bmciColors table should appear in order of importance.

Alternatively, for functions that use device-independent bitmaps, the 
bmciColors field can be an array of 16-bit unsigned integers that 
specify an index into the currently realized logical palette instead of 
explicit RGB values. In this case, an application using the bitmap must 
call device-independent bitmap functions with the wUsage parameter 
set to DIB_PAL_COLORS.

Note	The bmciColors field should not contain palette indexes if the 
bitmap is to be stored in a file or transferred to another application. 
Unless the application uses the bitmap exclusively and under its 
complete control, the bitmap color table should contain explicit 
RGB values.



BITMAPCOREHEADER  [3.0]

Device-Independent Bitmap Format Information
The BITMAPCOREHEADER structure contains information about the dimensions 
and color format of a device-independent bitmap that is compatible with 
Microsoft OS/2 Presentation Manager versions 1.1 and 1.2 bitmaps.

typedef struct tagBITMAPCOREHEADER {
        DWORD   bcSize;
        WORD    bcWidth;
        WORD    bcHeight;
        WORD    bcPlanes;
        WORD    bcBitCount;
} BITMAPCOREHEADER;

The BITMAPCOREHEADER structure has the following fields:

Field		Description
bcSize		Specifies the number of bytes required by the BITMAPCOREHEADER 
		structure. 
bcWidth		Specifies the width of the bitmap in pixels. 
bcHeight	Specifies the height of the bitmap in pixels. 
bcPlanes	Specifies the number of planes for the target device and 
		must be set to 1. 
bcBitCount	Specifies the number of bits per pixel. This value must 
		be 1, 4, 8, or 24. 

Comments	The BITMAPCOREINFO data structure combines the 
BITMAPCOREHEADER structure and a color table to provide a complete 
definition of the dimensions and colors of a device-independent bitmap. 
See the description of the BITMAPCOREINFO data structure for more 
information about specifying a device-independent bitmap.

An application should use the information stored in the bcSize field to 
locate the color table in a BITMAPCOREINFO data structure with a method 
such as the following:

pColor = ((LPSTR) pBitmapCoreInfo + (WORD) (pBitmapCoreInfo -> bcSize))



RGBTRIPLE  [3.0]

RGB Color Structure
The RGBTRIPLE data structure describes a color consisting of relative 
intensities of red, green, and blue. The bmciColors field of the 
BITMAPCOREINFO data structure consists of an array of RGBTRIPLE data 
structures.

typedef struct tagRGBTRIPLE {
        BYTE    rgbtBlue;
        BYTE    rgbtGreen;
        BYTE    rgbtRed;
} RGBTRIPLE;

The RGBTRIPLE structure contains the following fields:

Field		Description
rgbtBlue	Specifies the intensity of blue in the color. 
rgbtGreen	Specifies the intensity of green in the color. 
rgbtRed		Specifies the intensity of red in the color. 



-----------------------------------------------------------------------

	Non official comments

How to distinguish between BITMAPINFO and BITMAPCOREINFO when reading
in a BMP file.

After reading the BITMAPFILEHEADER read the next DWORD from the file. 
If it is 12 you are reading a BITMAPCOREHEADER, if it is 40 you are
reading a BITMAPINFOHEADER.