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-This code originally hails from IBM.  It was ported to an early XFree86 by
-Gertjan Akkerman, whose BUGS file I append here.
-
-In turn, this is a port of Gertjan's work to the new server design.  Among the
-changes are:
-
-- The removal of almost all unreferenced code.
-- The removal of this code's own copy of mfb (xf1bpp is used instead).
-- The removal of banking support (mibank is used instead).
-- External symbols were made static where this was sufficient.
-- The remaining external names were renamed to xf4bpp*.
-- Several minor cleanups too many to mention here.
-
-To understate the matter, this code is >UGLY<.  This seems inherent in IBM's
-corporate culture.  Be that as it may, it *does* survive X11R4's xtest
-(whatever that means these days...).  For now, this is sufficient for 4bpp
-support in the new design, but at some point, I'll have to sit down and
-rewrite this from scratch.  A more technical justification for a rewrite is
-that the pixmap format is 8bpp, instead of 4bpp, which is causing me to
-pepper the rest of the server with unclean accomodations.
-
-Marc.
-
-===============================================================================
-Section 1: From IBM's X11R4 contribution towards XFree86.
-
-This section describes what I did to obtain a 16 colour vga server.
-
-I started with the SYSV, ppc, vga and common directories from IBM's X11R4
-contribution. Those directories have the following function:
-1. SYSV implements the mouse and keyboard.
-2. ppc is a generic layer implementing ddx in terms of drawing operations
-   through rectangles. (With spans as a boundary case: height = 1.)
-3. vga implements a layer of operations drawing through rectangles.
-4. common implements ddx initialization and quitting, and screen saving.
-
-I eliminated SYSV and common since the functionality provided therein is
-already provided in XFree86. Since XFree86 is actively being ported to
-new operating systems, while X11R4 is out of date, I preferred the XFree86
-code here above the SYSV and common code.
-Whatever functionality was still needed from common (default colormap
-initialization -- not much code) was moved into ppc.
-
-Since XFree86 uses the mi-provided software cursor code, IBM's software
-cursor code was deleted from ppc and vga. This is a pity, since it is
-expected that it is more efficient than mi's code, but the XFree86 mouse and
-keyboard code directly call mi, and I do not want to maintain the XFree86
-mouse and keyboard code.
-
-Since we cannot support a monolithic multi-screen server using all of the
-x11r4 contributed code yet, all multi screen code was deleted. This includes
-one header file containing a nasty copyright statement.
-
-Since glyph handling has changed between X11R4 and X11R5, the code handling
-glyphs was replaced by appropriate calls to mi.
-I hope it can be modified and put back one day.
-
-Provisionally, some code was added (viz. file vga/offscreen.c) to intercept
-calls to the rectangle drawing code when we are switched out of the VT.
-I hope this can be replaced by some window tree invalidation and GC validation
-scheme.
-
-
-Section 2: BUGS
-
-This section describes fixed and still unfixed bugs in this code.
-All bugs not labeled otherwise also occur in IBM's X11R4 code, and may be of
-interest to anybody using that code.
-
-1. (Fixed.)
-I found (and provisionally fixed) a bug in the IBM bitblit code:
-In file ddx/ibm/vga/vgaImages.c a function vgaReadColorImage is defined.
-When this function is used to read less than 8 pixels starting on a byte
-boundary it will always read precisely 8 pixels.
-Thus, when space is allocated for 4 or less pixels, it will write beyond
-the allocated space.
-Since the code is rather convoluted, this may not be apparent at first sight,
-but going through the code with an example shows the error.
-
-2. (Fixed.)
-In ppcPixmapFS.c, function ppcStipplePixmapFS there was a bug
-regarding the stipple origin: The horizontal origin is added while
-the vertical one is subtracted. The horizontal origin should be subtracted
-instead of added here.
-This bug gets visible when backing-store is enabled and one uses twm:
-the submenu icons get truncated on their left hand side.
-(In case you wonder why this bug appears: under those circumstances
-twm prepares its menus by drawing into an unmapped window. 
-The miCopyPlane function uses the ppcStipplePixmap (and many others)
-to get the plane copied.)
-I also fixed this bug in the other routines (ppcOpStipplePixmapFS,
-ppcTilePixmapFS) in this file, although I had no visible clues for this.
-I hope this is appropriate.
-
-3. (Fixed.)
-I find it suspect that ppcSetSpans gives different output when one
-claims that an actually sorted list of spans is unsorted.
-The unsorted code is wrong, and should be made to look more like the sorted
-code. I.e., use ( xStart - ppt->x ) instead of ( xStart - pbox->x1 )
-
-4. (Fixed.)
-There used to be another bug that became visible when using twm and backing
-store: popping up a submenu, and moving the cursor upwards til it leaves the
-submenu, the submenu would disappears, as it should.
-But the submenu icon would not get restored, while it should be.
-10b. By replacing the clip-computing code in ppcValidateGC by that in
-cfbValidateGC, I *finally* fixed the disappearing twm menu icon problem.
-
-5. Added mfbRegisterCopyplaneProc call. [Its omission was an error on my
-   part.]
-   Fixing a server core dump in XTest.
-
-6. Fixed not-very-high tile bug in function ppcTileRect, file emulTile.c
-   (I.e., if the tile was higher than the area to be tiled, far too much
-   was drawn, causing server core dumps in XTest.)
-   Actually, "savey" ought to be used to determine the height of the tiles in
-   the top line to be tiled, instead of "pTile->drawable.height".
-7. A use of height where width was intended was fixed in ppcTileRect:
-   "savehcount = w / pTile->drawable.height;" should use "... .width" and
-   "savehcount = ( x + w - htarget ) / pTile->drawable.height;" too.
-
-8. Deleted overly clever code in ppcCReduce.c
-   (All code that tried to pre-compute how alu's could be replaced by
-    other alu's with inverted colors, etc. was deleted. I think it is
-   at least wrong for FillSolid.)
-
-9. Looked at suspicious code in ppcSetSp.c
-   "tmpx = *pdst;" was never updated during the loop. We took it out of the
-   initialization position of the for and moved it into the loop.
-
-10. Add xSrc := GC->patOrg.x + pDrawable.x and ySrc := ... in ppcPixmapFS.c,
-   functions ppcStipplePixmapFS, ppcOpStipplePixmapFS, and ppcTilePixmapFS.
-   This because stipple and tile origins are taken relative to the drawable.
-   Also use a "modulo" function that gets the cases of a negative stipple
-   or tile offset right. (When the stipple origin is to the right of or
-   below the origin of the drawable.)
-
-11. File vgaSolid.c, function vgaFillSolid:
-   Inverting is XORing with all ones. Not with the color we want to AND/OR
-   later. So we'll have to set the color to VGA_ALLPLANES
-   whenever we want to invert existing data, and reset it before the
-   AND/OR is done.
-   Also we replaced an outb( 0x3CF, tmp2 ) by the SetVideoGraphicsData( tmp2 )
-   it is representing. (Just a cosmetic replacement.)
-
-12. File vgaImages, function vgaDrawColorImage.
-   Moved a line "invert_existing_data = TRUE;" two lines down, past a case
-   label. Now it is also part of the code executed for GXorReverse, as it
-   should be.
-
-13. The pixmap FillSpans routines (file ppcPixmapFS.c) got somewhat better
-   after importing some code from ddx/ibm/vga. (A getbits function that does
-   wrapping.)
-   They were wrong for the FillStippled and FillOpaqueStippled modes.
-   I don't understand the old code. How could it handle stipples of a size not
-   an exact multiple of 32? (or 8, for that matter.)
-
-14. In function vgaBitBlt file vgaBitBlt.c, in the shortcuts for
-    GXSet, GXClear and GXInvert, the source (x0,y0) is accidentally operated
-    upon by vgaFillSolid, instead of the destination (x1,y1).
-
-15. Notice that in DoMonoSingle and DoMonoMany in file vgaStipple.c, the left
-   edge of the square to be stippled is treated wrong.
-   Correct would be to get the bits with getbits using offset xshift, and
-   to shift them right (x & 07) places. 
-   [One might wish to use the variable tmp1 at this place, since it had been
-    set to (x & 07) at this place; but that is already re-used at this point.]
-   Also note that NeedValX is set wrong: The implicit assumption was that
-   stipples are more than 8 wide.
-   This only fixes the problem when miPushPixel is used instead of ppcPushPixel.
-   I think I should look some more into this.
-   
-16. I took out some code of the CopyArea function, in which a no-op function
-   was called while a real one was needed. My fix does not completely work,
-   although it improved the behaviour of GetImage somewhat.
-
-17.  After finding three kinds of errors in this single function,
-   -- the new kinds being the right side not being always written due to
-   an incorrect if scope, and the lower end not always being written due
-   to variables being updated at the wrong place --
-   (requiring modifications to be made at at least 10 places,
-   I decided to REWRITE the body of the ppcTileRect function from scratch.
-   This version simply computes all relevant margins in advance, and does
-   not try to reuse temporary variables. I leave that to the compiler.
-   (This was a maintenance and robustness nightmare anyway.)
-
-MORE NOTES:
-   It is funny that there are two files in mi that require compilation
-   with the proper #defines ( -DXF86VGA16  in my case ):
-   Besides the obvious mibitblt.c, there is also mipushpxl.c.
-
-
-
-$XFree86: xc/programs/Xserver/hw/xfree86/xf4bpp/NOTES,v 1.1.2.2 1998/06/27 15:15:45 dawes Exp $