CS 686

PROJECT 1		               Due Date: Noon Thursday 10/16/2003

     The purpose of this project is to acquaint students with fundamental
programming issues involved in adapting legacy PC graphics software so it
can be executed as an SVGA application by a contemporary Linux system. 


                        PROJECT STATEMENT

     Modify the source-text for the 'polyfill.cpp' program (available for
copying from our class website) so it will execute correctly under Linux.
That program was written as a demonstration of the Bresenham Line-Drawing
algorithm as used for implementing polygon fill operations.  The compiler
for which its code was designed was Borland's popular TURBO-C++ compiler,
used to build applications for the MS-DOS operating system.  All hardware
and firmware capabilities upon which that software depends have continued
to be supported by modern PC systems, but the system software environment
provided by Linux differs from that of MS-DOS in several significant ways
that affect this application, including the following:     

Linux is a virtual memory, protected-mode, multitasking operating system
which adheres to certain user-interface standards for UNIX systems.
	
Any physical memory which needs to be accessed by an application program 
must be "mapped" by the Linux kernel to virtual addresses located within 
the region allocated for unprivileged access (i.e., in the address-range
from 0x00000000 to 0xC0000000).  These mappings are performed by calling
the 'mmap()' function on an already opened device-file.    

Any direct i/o programming of peripheral hardware, such as SVGA graphics 
controllers, requires that the application must be allowed to adjust the
IOPL field in the processor's EFLAGS register, an operation normally not
permitted unless arranged by the system administrator.  If allowed, this
adjustment will be accomplished by calling the 'iopl()' function with an
argument equal to 3.

Any deviations that are desired from the computer terminal's 'canonical' 
mode of handling user-input from the keyboard will need to be explicitly 
programmed, using standard API functions and data-structures.  The "raw"
keyboard input (unbuffered) that was always available to MS-DOS programs
is not a feature of the default keyboard behavior under Linux.     

Any use of routines in the SVGA manufacturer's ROM-BIOS firmware, to set
graphics display modes or perform other "low-level" graphics operations,
will require programs written in C/C++ to employ a special interface for
transmitting the function parameters which those routines expect to find
in specific CPU registers.  This issue also was present with MS-DOS, and
can be handled in a similar (though not identical) way under Linux, with
the LRMI library (provided as part of the SVGALIB package).  The library
also allows the real-mode ROM-BIOS instructions to execute transparently
in the Pentium's so-called Virtual-8086 mode.

The GNU C++ compiler for Linux uses some differently-sized data objects,
such as 32-bits for 'int', and enforces stricter rules for the declaring 
of constants and functions, than did the TURBO-C++ compiler for MS-DOS.  
________________________________________________________________________
Allan B. Cruse         University of San Francisco             Fall 2003