'BMP_EXAMPLE.BAS
'Copyleft 2012, M. Eric Carr / Paleotechnologist.Net
'eric (atsign) paleotechnologist (dot) net
'This code is placed in the public domain.


'Output of graphical data to a .BMP file, serving as
'an example of how the BMP header format works.
'(FreeBASIC has this functionality built-in, using the BSAVE function.)


'Output is a sample 3x3, 24-bit bitmap (colors are in BBGGRR order):

' 000000    800000      FF0000
' (black)   (dk blue)   (blue)

' 008000    808000      FF8000
'(dk grn)   (dk cyan)   (blue-cyan)

' 00FF00    80FF00      FFFF00
' (green)  (grn-cyan)   (cyan)


dim as ubyte fs1, fs2, fs3, fs4
dim as ubyte xs1, xs2
dim as ubyte ys1, ys2

dim as ulongint filesize, xsize,ysize,bmpsize,linesize
dim as ulongint fstemp, bstemp, xstemp, ystemp
dim as ulongint lineadj, x, y, pad



open "test1.bmp" for output as #1

xsize = 3
ysize = 3

'Compute the correct line size (padded to a multiple of four bytes)
linesize = xsize * 3
lineadj = 4-(linesize mod 4)
if lineadj=4 then lineadj=0
linesize = linesize + lineadj

'Compute bitmap size and file size
bmpsize = linesize*ysize
filesize = 26 + bmpsize


'Split filesize into four bytes. This would be easier in C, but
'the approach used here works.
fstemp = filesize
fs1 = fstemp mod 256
fstemp = (fstemp-fs1)/256
fs2 = fstemp mod 256
fstemp = (fstemp-fs2)/256
fs3 = fstemp mod 256
fstemp = (fstemp-fs3)/256
fs4 = fstemp mod 256

'Split xsize (image width in pixels) into twp bytes
xstemp = xsize
xs1 = xstemp mod 256
xstemp = (xstemp-xs1)/256
xs2 = xstemp mod 256

'Split ysize (image height in pixels) into two bytes
ystemp = ysize
ys1 = ystemp mod 256
ystemp = (ystemp-ys1)/256
ys2 = ystemp mod 256



'BMP file type header
print #1, "BM";

'File size, in bytes (Little-Endian)
print #1, chr$(fs1);chr$(fs2);chr$(fs3);chr$(fs4);   

'Reserved (2 bytes)
print #1, chr$(0);chr$(0);

'Reserved (another 2 bytes)
print #1, chr$(0);chr$(0);

'Offset for start of bitmap data
print #1,chr$(26);chr$(0);chr$(0);chr$(0);

'Bytes in the rest of the header (from this point on) (Little-Endian)
print #1,chr$(12);chr$(0);chr$(0);chr$(0);

'Width of bitmap, in pixels (Little-Endian)
print #1, chr$(xs1);chr$(xs2);

'Height of bitmap, in pixels (Little-Endian)
print #1, chr$(ys1);chr$(ys2);

'Number of color planes (Little-Endian)
print #1, chr$(1);chr$(0);

'Bits per pixel (Little-Endian)
print #1, chr$(24);chr$(0);


'Start of bitmap data. Normally, this would execute two nested loops
'over the rows and columns. For now, we will simply output the data
'row by row and pixel by pixel:

' 000000    800000      FF0000      Top row
' 008000    808000      FF8000      Middle row
' 00FF00    80FF00      FFFF00      Bottom row

'The rows are stored bottom-to-top, so they will be output 
'in that order.

'==================================================================

'Bottom left pixel
print #1, chr$(00);chr$(255);chr$(00);

'Bottom center pixel
print #1, chr$(128);chr$(255);chr$(00);

'Bottom right pixel
print #1, chr$(255);chr$(255);chr$(00);

'Three more bytes to pad the row from 9 to 12 bytes (a multiple of four)
print #1, chr$(00);chr$(00);chr$(00);


'Middle left pixel
print #1, chr$(00);chr$(128);chr$(00);

'Middle center pixel
print #1, chr$(128);chr$(128);chr$(00);

'Middle right pixel
print #1, chr$(255);chr$(128);chr$(00);

'Three more bytes to pad the row from 9 to 12 bytes (a multiple of four)
print #1, chr$(00);chr$(00);chr$(00);


'Top left pixel
print #1, chr$(00);chr$(00);chr$(00);
    
'Top center pixel
print #1, chr$(128);chr$(00);chr$(00);

'Top right pixel
print #1, chr$(255);chr$(00);chr$(00);

'Three more bytes to pad the row from 9 to 12 bytes (a multiple of four)
print #1, chr$(00);chr$(00);chr$(00);



close #1