From: varobert AT colba DOT net
Message-Id: <3.0.32.19990715123307.007add30@mail.colba.net>
X-Sender: varobert AT mail DOT colba DOT net
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Date: Thu, 15 Jul 1999 12:33:08 -0400
To: djgpp AT delorie DOT com
Subject: Re: Allegro shading, once again I'm lost
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Reply-To: djgpp AT delorie DOT com

It depends: if your bitmaps are all 256 colors on disk, you can load them
as 256 color images like so:
set_color_depth(16);
get_gfx_mode(...);
//... your code
set_color_depth(8); //This will not change screen modes, but rather how
Allegro loads images.
BITMAP *mybmp = load_bitmap(file);
set_color_mode(16);
//...more of your code


so now you can address them as 8-bit color bitmaps the way you described.

Now, if your bitmaps are 16-bit color on disk, then you could do something
like that:

int k = ((short*)BMP->line[y])[x];
int r = getr(k) * shade / 256, g = getg(k) * shade / 256, b = getb(k) *
shade / 256;

((short*)BMP->line[y])[x] = makecol(r,g,b);

There are, of course, ways to optimize this (with a look up table for each
color component, etc. ).

Or, you could always use a 16MB array of [65536][256]...

- GodOfWar


At 08:58 AM 7/14/99 -0400, you wrote:
>First of all, sorry to be posting the (almost) same question, but I'm
>still lost...
>
>Lets say I have a 256-color BMP in 8 bit color mode.  So something like
>this:
>
>BMP->line[y][x]
>
>will return a value between 0-255.  So, if I needed, I could use this
>value as the subscript for an array, like this:
>
>
>Color = ShadePalette[  BMP->line[y][x]  ] [ 0 ] 
>		       ^^^^^^^^^^^^^^^      ^
>                         Color Index    Shading Index
>
>Now for the question... In 16-bit color mode, the BMP->line[y][x]
>returns a 16-bit number, which ranges from 0 to 65535.  Now, its pretty
>hard to have an array that is like this: ShadePalette[65535][255]   Its
>a little too big!  So using it as an array subscript is out of the
>question.  So, how do I use a LUT for shading in 16-bit color mode?  Or
>is there another way?
>
>
>Thanx in advance!!
>
>