BSD 4_3_Tahoe development

Work on file usr/src/new/X/libibm/bitblt/README

Synthesized-from: CSRG/cd2/4.3tahoe

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+General information about Bitblt:
+
+If you look at the Makefile you will see that there are five defines
+used during the compilation of bitblt. The Makefile is distributed this
+way so that bitblt is able to run on all of the currently available IBM
+displays. Lets take a closer look at each define.
+
+APA16          The bltter is compiled to run on the apa16 display.
+               (Note: The apa16 has hardware cursor support)
+
+USE_APA16_HDWR The bltter will use apa16 hardware features to
+               do screen to screen copies and and selected tiling
+               operations. Note that it only makes sense to define 
+               this when APA16 is also defined.
+
+APA8           The bltter is compiled to run on the apa8 display.
+               (Note: The apa8 and apa8c have software cursors)
+
+APA8C          The bltter is compiled to run on the apa8C display.
+               (NOTE: FULL COLOR SUPPORT IS NOT PROVIDED)
+
+AED            The bltter is compiled to run on the aed display.
+               (Note: The aed has hardware cursor support)
+
+Note: 
+       When none of the above are defined this creates a bltter that
+       will work on any bitmap display (within limits). This includes
+       the PQD. That is why no define was provided for it.
+
+It should be noted that only those defines that relate to your hardware
+configuration need be used (or none at all). This would in most cases reduced
+code size and improve performace by 0 - 5 percent. Since the performance hit
+for having the bltter compiled to run on all displays is minimal, consideration
+should be given to the flexability provided by doing so.
+
+
+Now lets review the source files.
+
+bitblt.c       This is the code that actually does the the blt.
+
+bitblt_apa16.c These two files make up the apa16 hardware support.
+bitblt_apa16.h
+
+bitblt_aed.c   These two files make up the aed microcode support.
+bitblt_aed.h
+
+bitblt_subr.c  This file contains the code required to convert the 
+               extrenal bitblt data structure to and internal structre
+               for easy processing.
+
+bitblt_cur.c   This file contains the software cursor support. The code
+               that removes the cursor from the screen and puts it back
+               is in the kernel. The code that informs the kernel of where
+               the current blt is taking place is in this source file.
+
+               Note: Since hardware cursors are not removed from
+                     the screen during a blt the support can be done
+                     in the kernel. Therefore, the code is not included
+                     in this source file.
+
+               Before the bltter is used bitblt_init() must be called
+               to set the cursor type and bitmap address. The cursor
+               types are SOFT_CURSOR and HARD_CURSOR.
+
+bitblt_int.h   This file contains the internal data structures.
+
+bitblt_ext.h   this file contains the external data structures.
+
+
+For more information on bitblt see bitblt.paper in the doc directory.
+
+                               
+                                               -- Scott --