Re: [ql-users] C structures

[Phoebus Dokos]

On Sat, 12 Jul 2003 08:49:49 +0100, Dilwyn Jones <[EMAIL PROTECTED]> 
wrote:

Phoebus Dokos wrote:

You could also get BMP2SCR from Malcolm and use it in reverse
(trivial to
do so and from the quick look I gave to your code you're on the
right
track).
Just had a quick look (it's on disk GE104 in my PD library) . However,
it doesn't explain the file structure except how to check it's 24 bit
and picture size. But it does show how to do the approximation of 24
bit colour to 16 bit QL colour (i.e. how to convert 8 bit RGB
component to 5 or 6 bit GD2 colour components - simply lop off the
extra info, you then simply get coarser steps of colour, so instead of
values 0-31 for a bit GD2 colour you get 0-255 step 8 in 24-bit
colour). A bit mind bending for a simpleton like me, but I'll get
there ;-)
<snip>


The complete file format ('new' format which is the most common) (more like 
the complete header of the BMP format is as follows):

Offset 	Field		Size		Contents
000h		Id		2 bytes	(Insert here 'BM' for BMP image file. Other options are 
possible as well)
002h		FSIZE		4 bytes	Full file size in bytes
006h		RESVD	4 bytes	Reserved (Pad with 0s)
00Ah		BMPD_OFF	4 bytes	Offset of the beginning of bmp data from the 
beginning of file
00Eh		BMPH_SZ	4 bytes	Length of the BMP Info Header (what describes bmp 
colours, compression... possible sizes are:28h - Windows, 0Ch OS2 1.x, F0h 
OS 2.x
012h		WD		4 bytes	Width of image in pixels
016h		HT		4 bytes	Height of image in pixels
01Ah		PL		2 bytes	# planes in the picture (not the flying kind ;-)
01Ch		BPP		2 bytes 	BPP used for palette info. (Possible colours of sorts). 
Possible values
1 - Mono, 4 - 16 colours, 8 - 256 colours, 16 - High colour, 24 - 24 bit 
colour, 32 - 32 bit colour
01Eh		CMP_SPEC	4 bytes	Compression Specs. Possible values: 0 - none (Also 
BI_RGB), 1 - RLE 4bit/pixel (Also BI_RLE4), 2 - RLE 8bit/pixel (Also 
BI_RLE8), 3 - Bitfields (Also BI_BITFIELDS)
022h		BMP_DSZ	4 bytes	Size of the bitmap DATA in bytes. Must be rounded to 
the next 4 byte boundary.
026h		HRES		4 bytes	Horizontal res in pixels/meter
02Ah		VRES		4 bytes	Vertical res in pixels/meter
02Eh		COL		4 bytes	Number of colours used by this bitmap (ie for an 8bit 
colour image: 256)
032h		IMPCOL	4 bytes	Number of important colours (equal to COL above if 
every colour is important)
036h		PAL		n*4 bytes	Palette Specs. For every entry in the palette, 4 bytes 
describe the RGB values as follows: 1 byte:blue, 1 byte: green, 1 byte red, 
1 byte filler (filled with 0)
436h		BMP_DATA	n bytes	Depending on CMP_SPEC, all bitmap data bytes that 
represent indices in colour palette

Now since a Type structure is impossible in SBasic, you should use an Array 
to conveniently manipulate all this blah-blah.
However to save space you should remember that there is a MAXIMUM size of 
the header (and that occurs when a palette exists).

Also to try to go through the hoops and produce every possible combination 
would be irrational (IMVHO) and I would recommend you use only the 24bit 
option, as it simplifies calculations. Not to mention that you can have the 
rest of the info hard coded for all screen sizes mode 32 and 33 support.
Moreover, in Mode 33 (and you should include Mode 33), remember the 
importance of the Intensity (Extra Green bit) and cater for that in the 
translation.

Hope this helped a bit,

Phoebus



--
Phoebus Dokos - Undergrad in MIS
Eberly College of Business - Indiana U. of PA