ex12bit(3alleg4)                 Allegro manual                 ex12bit(3alleg4)

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

       #include <allegro.h>

       Example ex12bit

       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

       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).

       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), rest(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)

Allegro                           version 4.4.3                 ex12bit(3alleg4)