🚀 go-pugleaf

itwill@techfak.uni-bielefeld.de (Torsten Will) writes:
>of course. But in 16color mode the result is only in two colors -- every bit is 
>a pixel. In 256color mode I can not access the full area of the screen (but every
>byte is a pixel, how I expected). I don't want to set every single pixel with
>a Interrupt because it MUST be possible to write fast to the screen -- in 16 colors
>and/or two the whole screen area.

Of corse you don't have to use the slow video bios.
What is hapening is that you are only writing to one bit plane.
See the video cards memory is divided into four bit planes each 64KB
in size. These four bit planes can each be adressed at the host address
( A0000 to B0000 hex ) in any combination. The bit mask register determines
which plane will be addressed. It has a bit for each bit plane i.e. four
bits.

In 16 color mode what determines the color of a pixel is the four bits.
bit 0 comes from plane 0 offset X and bit n ( where n is the bit at location
A0000h + X )
bit 1 comes from plane 1 offset X and bit n
"   2  "      "   "    2  "     "  "   "  " 
"   3  "     "    "    3  "     "  "   "  "
			adam   email s921880@minyos.xx.rmit.oz.au