From: KC5TJA <kc5tja@topaz.axisinternet.com>
  To  : ggi-develop@eskimo.com
  Date: Sun, 5 Jul 1998 13:00:18 -0700 (PDT)

Re: kgicon difficulties |-< (and new tarballs |->)

> which is like the code in lib/libggi/default/linear-4/*, whereas VGA 4
> bit mode is a weird thing called "ModeX" and needs code like the stuff
> in kgi/lib/libggi/IBM/*.

Bitplane mode is not in any way "weird".  Bitplane techniques have been in
use for far longer than packed pixel modes.  If anything, it's the packed
pixel modes that are foreign to the VGA architecture.

> Also, is the 640x400x4bit mode banked ?  It must take up at least 128K,
> but the window at A0000 is usually only 64K (again AFAIK, which aint
> much).

While this is true, keep in mind that only one bitplane is visible to the
CPU (note: multiple bitplanes may be physically affected by the CPU
depending on VGA register settings; but still, only ONE bitplane is
visible to the CPU at any one time).  640x480 is 307,200 pixels.  However,
since there are eight pixels per byte, a single plane consists of only
38400 bytes of memory.  This fits quite nicely within the 64K bank for the
frame buffer.

In fact, 800x600, 4 bitplanes will fit within the VGA's 256K memory
architecture, and can be used just as with 640x480 mode, without banking.

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