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ex12bit(3alleg4)


NAME

   ex12bit - How to fake a 12-bit truecolor mode on an 8-bit card. Allegro
   game programming library.

SYNOPSIS

   #include <allegro.h>

   Example ex12bit

DESCRIPTION

   This program sets up a 12-bit mode on any 8-bit card, by setting  up  a
   256-colour  palette  that  will  fool  the  eye into grouping two 8-bit
   pixels into one 12-bit pixel. In  order  to  do  this,  you  make  your
   256-colour  palette  with  all  the  combinations  of  blue  and green,
   assuming green ranges from 0-15 and  blue  from  0-14.  This  takes  up
   16x15=240  colours.  This  leaves  16 colours to use as red (red ranges
   from 0-15).  Then you put your green/blue in one pixel, and your red in
   the  pixel  next  to it. The eye gets fooled into thinking it's all one
   pixel.

   The example starts setting a normal 256 color  mode,  and  construct  a
   special  palette for it. But then comes the trick: you need to write to
   a set of two adjacent pixels to form a single 12 bit dot. Two eight bit
   pixels is the same as one 16 bit pixel, so after setting the video mode
   you need to hack  the  screen  bitmap  about,  halving  the  width  and
   changing  it to use the 16 bit drawing code. Then, once you have packed
   a color into the correct format (using the makecol12() function below),
   any  of  the  normal Allegro drawing functions can be used with this 12
   bit display!

   Things to note:

   The horizontal width is halved, so you get  resolutions  like  320x480,
   400x600, and 512x768.

   Because  each dot is spread over two actual pixels, the display will be
   darker than in a normal video mode.

   Any bitmap data will obviously need converting to the  correct  12  bit
   format: regular 15 or 16 bit images won't display correctly...

   Although  this  works like a truecolor mode, it is actually using a 256
   color palette, so palette fades are still possible!

   This code only works in linear screen modes (don't try Mode-X).

SEE ALSO

   BITMAP(3alleg4),         END_OF_MAIN(3alleg4),         MATRIX(3alleg4),
   PALETTE(3alleg4),         RGB(3alleg4),         allegro_error(3alleg4),
   allegro_init(3alleg4), allegro_message(3alleg4), apply_matrix(3alleg4),
   blit(3alleg4),          circle(3alleg4),         clear_bitmap(3alleg4),
   clear_keybuf(3alleg4), clear_to_color(3alleg4), create_bitmap(3alleg4),
   create_bitmap_ex(3alleg4),                     destroy_bitmap(3alleg4),
   ellipsefill(3alleg4),        fade_out(3alleg4),        fixcos(3alleg4),
   fixed(3alleg4),    fixsin(3alleg4),   fixtoi(3alleg4),   font(3alleg4),
   get_rotation_matrix(3alleg4),                        getpixel(3alleg4),
   install_keyboard(3alleg4),     itofix(3alleg4),    keypressed(3alleg4),
   line(3alleg4),         makecol(3alleg4),          masked_blit(3alleg4),
   putpixel(3alleg4),       screen(3alleg4),       set_clip_rect(3alleg4),
   set_color(3alleg4),    set_gfx_mode(3alleg4),     set_palette(3alleg4),
   text_height(3alleg4),     text_length(3alleg4),    textout_ex(3alleg4),
   textprintf_ex(3alleg4)



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