VER246.TXT	29-Jul-2004

Version 2.4.6 of the XPL0 runtime code (Native and I2L) fixes some
problems with background colors when using text in graphic video modes,
and runs some graphic routines much faster than before.

There are also some bug fixes. The worst bug, introduced in version 2.4,
involved the combination of the Restart intrinsic (6) and segment
variables. The problem was that the extra segment register (ES) did not
point to the program segment prefix (PSP) when the program restarted.
Thus after a call to Restart, the internal runtime variable PSPSEG was
corrupted. This affected the Resize routine, which is called at the
beginning of every XPL0 program, as well as the Shrink (78) and Chain
(28) intrinsics. The Malloc intrinsic (73) was also indirectly affected.

The break vector ($1B) has been fixed...again. The code that preserved
the divide-by-zero vector broke the break vector, which was worse, so the
code has been restored to its original form. This means that the
divide-by-zero vector is not restored if a Ctrl+C or Ctrl+Break is used
to exit an XPL0 program. Any programs that were compiled with Native
versions 2.4.3 through 2.4.5 do not restore the break vector. Thus after
running one of these programs, hitting Ctrl+Break will jump to an
undefined memory location (i.e. will blow up). Any XPL0 .EXE file with a
date after April 14, 2002 should be recompiled. This problem did not
occur in the interpreted version, which produces .COM files.

A bug involving the 'for' loop control variable in the optimizing, XPLX,
compiler has been fixed. The conditions under which this bug occurred
were extremely unusual. They involved using a 'for' loop control variable
defined at an intermediate level (not global or local) and referenced
inside a loop (such as a while, repeat, or loop).


COLORED TEXT

The SetWin intrinsic (70) now fills and scrolls the proper background
color when the display is set in graphic modes, such as with SetVid($12).
In other words, colors set by the Attrib intrinsic (69) for output device
6 now work in graphic modes the same as they have always worked for text
modes (except flashing).

Characters displayed in video mode $13 can have 256 colors for both their
foreground and background. Previously the background was always black
(color 0). In this mode the Attrib intrinsic uses all 16 bits of its
argument, not just the low two nibbles that are used to specify the
foreground and background colors for all the other modes. The high byte
specifies the color of the background, and the low byte specifies the
color of the foreground.


FASTER GRAPHICS

The Point intrinsic (41) now runs about 70 times faster in graphic mode
$13, and runs 5 times faster in planar modes such as mode $12. This
amazing speed increase was accomplished by accessing the VGA registers
directly (as was already done by the Line intrinsic) rather than by
calling BIOS routines. CGA modes 4, 5, and 6 still call BIOS like before.

The Line intrinsic (42) now draws horizontal lines up to 4 times faster
in planar graphic modes ($0D to $12). This was accomplished by replacing
REP MOVSB with REP STOSW. Almost all the time it takes to execute the
Line routine is in this single instruction because I/O is so incredibly
slow. Using words instead of bytes gives a 2-times speed increase; and
avoiding the read with MOVS, which is unnecessary for solid (non-dotted)
horizontal lines because all pixels in a word are overwritten, gives
another 2-times speed increase.


NVIDIA

XPL0's graphic routines compensate for a bug in the nVidia graphics
accelerator card's BIOS routines that causes a screen (or window) full of
vertical lines when calling the Clear or SetWind intrinsics. The problem
was caused by nVidia not resetting VGA registers to their default states.
(This is not just an incompatibility with XPL0, nVidia BIOS is
incompatible with itself.)

The worst problem with nVidia is that it does not generate the correct
sync signals for resolutions greater than 640x480 when running under
Windows XP. nVidia seems unconcerned about this despite numerous
complaints. The problem can be solved by unplugging the nVidia card,
using Windows 98 instead of XP, or by using an ATI accelerator card. XPL0
does not take advantage of any accelerator card features.


TRIVIA

MASM 6.11 does not assemble "JL $-2" optimally, so XPLX now generates
"DB 07Ch, 0FCh" instead.

-Loren Blaney