From: Emmanuel Marty <core@suntech.fr>
  To  : ggi-develop@eskimo.com
  Date: Mon, 06 Jul 1998 05:16:51 +0000

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

KC5TJA wrote:

> > want, without having to touch the other stuff.  However, one of the main
> > drawbacks of planar layouts is that they are considerably slower when it
> > comes to rapid software pixel-setting of the whole framebuffer.
>
> I find this to be questionable, actually.  For a given resolution with a
> given depth, both chunky and planar modes must exchange exactly the same
> amount of information.  One of the reasons that Mode X is so popular is
> because you can break it up into planes.  By setting the VGA to use planar
> chunky mode, a single 32-bit memory access can set all of 16 pixels
> concurrently!

That's not the issue. If you use a 8 bitplanes mode (for 256 colors), when
you want to change the color of a pixel, you have to change one bit
in eight different bytes, that means eight times reading one byte, masking
a bit out, oring the new value, writing the byte back ; whereas when
using a 256 color chunky pixel mode, you just _write one byte_, and
there, you have changed the color. Blitter or not, it's 1 operation instead
of 24 (worst case) and way less memory access ; considering that
accessing chip memory on the amiga was slllooowww.

Trust me for having written a doom-like engine on my amiga when I was
bored some night three years ago, the extra chunky->planar conversion
step needed is not fun.

--
Emmanuel