1. background colors
I'm trying to get the Text-GUI to support VGA mode, and am having a *lot* of
trouble working out how to get the background color to work.
When I do a call to bk_color(), it changes the text background color of
*all* the text that has been displayed. This obviously will not work for me,
since I need a lot of different background colors on the screen at the same
time.
For example, something like the following:
-- CODE BEGINS HERE ------------------------------------------------------
-- VGA mode
integer result
result = graphics_mode(18)
-- red text on white background
bk_color( WHITE )
text_color( RED )
puts( 1, "This is line 1\n" )
-- white text on red background
bk_color( RED )
text_color( WHITE )
puts( 1, "This is line 2\n" )
--- CODE ENDS HERE --------------------------------------------------------
will *not* work. I think this is because screen writes use the attributes
{text_color, bk_color}, and the redefinition of bk_color just changes the
pallette of the background color.
What I *really* want to do is write a different background attribute number
to the screen, not attribute zero. That way, I can hopefully get around the
problem of bk_color() redefining BLACK's pallette.
Is there a simple way that I can display text on the screen in graphics mode
18 that either (1) allows me to use multiple background colors, or (2) uses
the color that is already displayed in the background?
I've finally resorted to an interrupt, but the routine has problems:
-- CODE BEGINS HERE ------------------------------------------------------
procedure display( integer row, integer col, integer color, sequence char )
object lowMem
sequence inReg, outReg, cursor
lowMem = allocate_low( length( char ) ) -- get memory
poke( lowMem, char ) -- move description to memory
inReg = repeat( 0, 10 ) -- initialize register list
inReg[REG_AX] = #1301 -- tty string write
inReg[REG_BX] = #F0 + color -- video page/color
inReg[REG_CX] = length(char) -- number of characters to print
inReg[REG_DX] = row*#100+col -- position of cursor
inReg[REG_ES] = floor(lowMem / 16) -- segment of low_mem (low memory)
inReg[REG_BP] = remainder(lowMem, 16) -- offset of low_mem
outReg = dos_interrupt( #10, inReg ) -- bios call
free_low( lowMem ) -- free the memory
end procedure
-- CODE ENDS HERE -------------------------------------------------------
Note that I set a bit high in high byte of BL (I forgot which one, so I set
them all). If the bit is set to 0, the program will use the BLACK color
(#0). By setting the bit, it ORs the colors with the background.
Using this hack, I can display text that uses the underlying background
color - but I have to specify the *inverse* of the color, relative to the
background. This is a pain.
I *think* I can re-write the code by setting AL to 3 or 4, and poking the
string into memory as a { char, attribute } pair.
Needless to say, I'm hoping that there is a much simpler way of going about
this business.
-- David Cuny
