From:	"Tony Friery" <tony AT basoft DOT enta DOT net>
Newsgroups:	comp.os.msdos.djgpp
Subject:	Q: Creating Allegro Bitmap from Binary Data
Date:	Thu, 30 Sep 1999 18:17:24 +0100
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To:	djgpp AT delorie DOT com
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Reply-To:	djgpp AT delorie DOT com

Hi there,

I am currently writing an Emulator for the (now near-vintage) Sharp MZ-80B
and have a question regarding the Screen-Generator Code.

The Graphical Resolution is 2 simultaneous mono-planes of 320x200, and text
normally 40x25 using 8x8 font (Conveniently :) ) There is also an 80-column
mode which means an effective resolution of 640x400 which is what I have
chosen as the graphics mode.

At the moment, I use 5 bitmaps (eg FONTRAM, TEXTRAM, VID1RAM, VID2RAM,
TEMPRAM) in various resolutions and use a combination of stretch_blit, blit
and masked_blit to get them onto the screen.

With the text, this is normally OK (I pre-stretch into a temporary bitmap
beforehand as it will always be y*2 stretched anyway in order to save
overhead) but I need an efficient way of writing an 8-bit value into Video
Ram, without the following:

void FillBitmap(BITMAP (sbm, int begx, int begy, byte Data)
{
    int xl, colval;    /* xl is the X-Loop Variable */

    for (xl=0; xl<8; xl++)
    {
        colval=2*((Data>>xl) &1);
        putpixel(sbm, begx+(7-xl), begy, colval);
    }
}

Does this more efficient method exist? If so, can someone please point me in
the right direction :)

TIA
Tony Friery

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