GRIPS 2: Government Rast…rocessing Software & Data/GRIPS_2.cdr/dos/seq/readme.rev

Text File | 1990-01-06 | 8.9 KB | 193 lines

RASTER GRAHPICS ON IBM PCS

Introduction

The IBM PC raster graphics package consists of separate programs for
three different PC display adapters.  The Revolution 512x8 board from
Number Nine Computer Corp. offers the best aspect ratio and 256 colors
out of a full palette of 24 bits (16.7 million colors) on a roughly
512x480 screen.  IBM's Professional Graphics Adapter has the best
resolution of 640x480 and can display 256 colors from a palette of 12
bits (4096 colors).  The IBM Enhanced Graphics Adapter is a much better
choice for software compatibility, cost, and text mode work, but only
16 colors out of a palette of 6 bits (64 colors).

Source Code Files

Programs are available to display raster images, clear the graphics
screen, set individual palette entries, and load the entire palette from a
file.  Different source code is available for the different display adapters
that we support.  The source code's base file name (not the extension) is
suffixed by a character indicating the display adapter that it uses.   For
example, seqe.c is the image display routine for the EGA and seq9.c is the
display routine for the No. 9 card.  Each display adapter also has an assembly
language driver routine.  These are called no9.asm, pga.asm and ega.asm for
the No. 9 card, the PGA and the EGA respectively.

Raw Image File Format

Image files are raw binary files, one byte per pixel indicating a color value
from 0-255.  They are interpreted as a continuous stream of bytes, i.e. the
second line immediately follows the first line with no end of line or end of
record marker.  Note that this matches the "de facto" standard used on the
Sun systems.

Color map files

Raw palette files that we use consists of 256 bytes of the red entries
followed by 256 bytes of the green entries and then 256 bytes of the blue
entries.  Each entry in the color lookup table is composed of one byte from
each of the three component areas.  To get the Nth entry, the Nth
element(red), the (N+256)th element and the (N+512)th element are
combined to get the desired RGB value for the Nth color register.

Each display adapter handles color differently.  The [-m mapfile] parameter
causes seq to load the set of palette registers before displaying the image,
but color map files are interpreted differently for each display.

The No. 9 board uses a separate monitor, so the palette registers only
change when they are explicitly set.  Therefore, a program called 'paload'
is available, independent of seq9, to load palette files. Paload uses the
raw palette file format.  It takes one parameter, the name of the palette
file, and loads that data into the board's registers.  Color map loading can
take place before or after an image is displayed, allowing the user to change
color maps without re-displaying the image.

The PGA palette registers can only take entries from 0-15 for each of the
RGB components rather that the 0-255 range provide by the raw palette file
format.  For compatibility with the higher-end systems and the No. 9, the
color map files are identical to the ones used on the No. 9.  To handle the
lesser color capability of the PGA, each table entry is divided by 16 (retain
high order 4 bits) before being used.  There is no independent 'paload'
program for the PGA because the screen is continually getting reset to be used
as a console.  Instead, the color map can only be loaded by specifying a file
name on the command line of seqp with the [-m mapfile] parameter.

The EGA requires a very special color map file.  Our goal is to have all
the display programs use data which is one byte per pixel (0-255), but the
EGA can only display 16 colors.  To accomplish this, both a palette and
a special translation table is used.  On the command line, specification
of the palette file is the same as the others: [-m egamapfile].

The EGA palette file is an ASCII card image file containing a list of
272 numbers, one per line.  The first 16 numbers are the color map settings
as per IBM specifications.  Each number represents a palette register byte
meaning:  xxRGBrgb  to the EGA palette of 64 colors.  The next 256 numbers
make up the translation table.  Each number is in the range 0-15 and
corresponds to the EGA color to use for that particular data value.  The
first number is for data value 0, the second for data value 1, etc.  This
translation takes place on the fly, in the assembler code, so user programs
can manipulate the translation table to stretch the capabilities of the EGA's
16 colors to display data which is 8 bits deep.  An example of one of these
files is provided in the distribution.

Command Line Syntax

The grammar that I will use for describing the commands is quite simple.
The command name will be the first word on the line.  This may be followed
by nothing (no parameters), mandatory parameters or optional parameters.
Optional parameters will be enclosed in square brackets ('[]'), and mandatory
parameters will be enclosed in angle brackets ('<>').  If two items within
square brackets are separated by a pipe (|),  you may select one of the two,
but not both. <cr> indicates an end of line.

Raster Image Display Routines

The basic command line for calling seq is:

seq <xdim ydim> [-c | -p xwhere ywhere][-m mapfile] <fileofnames><cr>

xdim and ydim are the xdimension and y dimension of the image file(s) which
are to be displayed.  -c causes the image to be centered on the screen and
-p allows the user to pick a particular location for the upper left corner
of the image to be positioned.  -m will load a color map before
displaying the picture (see below).  'fileofnames' is the name of a file which
contains a list of file names which make up a sequence of image files to be
displayed in movie fashion. The way to display only one file is to place the
name of the image file into another textfile.  Optional parameters may be
specified in any order, but must occur between the image dimensions and the
'fileofnames'.  All of the images in the sequence are interpreted as
if they have the dimensions xdim,ydim.

The 'pflip' program can be valuable on the PGA, it enables a simple
keystroke to flip back and forth between the text and graphic displays.

Palette Manipulation and Creation Routines.

Several routines are available for the use and modification of color palettes.
You can change individual entries, load entire palettes from the color palette
files, and build palette files from text files.

The routine paload is available for the No. 9 card.  The syntax is:

paload <filename><cr>

This routine used the raw palette file, 'filename', to initialize the hardware
color lookup table.

Palset, also available for the No. 9 card, can be a one line command or it can
be used interactively.  The syntax for the one line command is as follows:

palset <entry_no> <red> <green> <blue><cr>

Entry_no is the register number of the entry that will be changed. Red, green
and blue are the RGB components that will be used to initialize the entry.
You can set more than one entry by using palset in interactive mode.  To do
this, enter palset <cr> on the command line.  Palset will then accept lines
of keyboard input of the form:
<entry_no> <red> <green> <blue>
where the meanings of the items are the same as above.  palset will continue to
accept lines until it sees a period as the first element on the line.  For
example, this interaction:

palset <cr>
1 0 0 0
10 30 30 30
100 112 0 0
.

will set the second color palette entry to black(0 for red, 0 for blue and 0
for green is black), the 10th entry to a shade of grey,  and the 100th entry
to a shade of red. You can also redirect input from a text file of this form
with the same result.  For example:

palset < <filename><cr>

can be used to set palette entrys according to the contents of the file,
'filename'.

Palbuild is a utility that you can use to create a raw palette file from
text of the same form used by palset.  The syntax is :

palbuild <newpalfile><cr>

or

palbuild <newpalfile> < <filename><cr>.

The first form of the command will wait for input from the keyboard terminated
by a period just as palset does.  The last form gets its input from the text
file 'filename', again just as palset.  This routine has no effect on the
hardware color look-up table.  Instead, it converts the input to the raw palette
file format that can be used by paload.

Miscellaneous Utilities

A routine called gclear is also provide.  This routine simply clears the
graphics buffer to all zeros.  The syntax is as follows:

gclear<cr>.

Another utility called init9 initializes the graphics hardware.  This routine
is only necessary on the No. 9 card, and is supplied by Number Nine Corporation.
The routine takes no parameters.

Questions and comments:
Thomas Redman
University of Illinois
National Center for Supercomputing Applications
152 Computing Applications Building
605 E. Springfield Ave.
Champaign, IL  61820
[phone]