Loadstar 15/015.d81/pps #37

Text File | 1985-01-01 | 4.7 KB | 285 lines

======================================
   PEEKs, POKEs, & SYSes -- Part 37

        By James Gelatin Weiler
          and Ailing Gardner
======================================

  Last time we told you that next

time we hoped to have a version of

the SYSPLOTTER routines that would

draw lines.  This time we can tell

you that we really do have what we

told you last time we would have next

time.

  For everyone who wasn't with us

last time, here's a reprise of what

you missed:

  SYSPLOTTER is a set of machine

language routines that make

high-resolution graphics work easily

and quickly from within a BASIC

program.  There are commands to turn

graphics on and off, to change the

background and pen color, to draw or

erase points, and to clear the whole

high-resolution screen.

  Now SYSPLOTTERB adds commands to

draw horizontal and vertical lines.

Here, again, is the complete list of

commands available:

======================================
  Bit-mapped graphics: how to do it
   using the SYSPLOTTERB routines.
- - - - - - - - - - - - - - - - - - -


  First, load the routines:


3 IFL=0THENL=1:LOAD"SYSPLOTTERB.O",8,1


After that, it gets simple fast.


A. SETGRAPHIC
   To set the bit mapped graphics
   mode, SYS 49152.

B. CLEARGRAPHIC
   To clear the graphics screen,
   SYS 49158.

C1.COLORSMEAR
   To set the background color,
   SYS 49161, <0-15>.

C2.PLOTCOLOR
   To set the "pen" color,
   SYS 49164, <0-15>.

D1.DRAW
   To plot a point,
   SYS 49167, <0-319>, <0-199>.

D2.ERASE
   To erase a point,
   SYS 49170, <0-319>, <0-199>.

E1.HRIZLINE
   To plot a horizontal line,
   SYS 49176,<0-319>,<0-319>,<0-199>

E2.VERTLINE
   To plot a vertical line,
   SYS 49173,<0-199>,<0-199>,<0-319>

F. UNGRAPHIC
   To turn off the graphics screen
   and return to the text screen,
   SYS 49155.

======================================

  Now the details.


SETGRAPHIC (49152), UNGRAPHIC (49155),

and CLEARGRAPHIC (49158) are just

simple SYSes.



SETGRAPHIC turns on the bit-mapped
 graphic screen with a base address
 of 8192.

UNGRAPHIC turns on the normal text
 screen.

CLEARGRAPHIC erases any bit-mapped
 pattern on the high-resolution
 screen.  It is equivalent to poking
 zeros into all memory locations from
 8192 to 16191.

- - - - - - - - - - - - - - - - - - -

COLORSMEAR (49161) & PLOTCOLOR (49164)

are SYSes that must be followed by a

comma and one numeric expression.

  The numeric expression should

evaluate from 0 to 15.  It selects the

color of the background or pen for the

entire screen.  The numeric expression

can be a constant, a variable, or

an expression.

Examples:

COLORSMEAR --

SYS 49161,2

 will change the backgrond color of
 the entire screen to red.


PLOTCOLOR --

Z = 0: SYS 49164,Z

 will change the color of all the
 plotted points on the screen to
 black.

- - - - - - - - - - - - - - - - - - -

DRAW (49167) and ERASE (49170) are

SYSes that must be followed by two

numeric expressions separated by

commas.  The first expression is

the horizontal position to plot and

should be in the range 0 to 319.

The second expression is the vertical

position and should be from 0 to 199.


Examples:

-- DRAW --
FOR A = 0 to 20
SYS 49167,A,A
NEXT A

 will draw a short diagonal line in
 the upper left corner of the screen.


-- ERASE --
FOR A = 0 to 10
SYS 49170,A*2,A*2
NEXT A

 will turn the diagonal line we drew
 in the previous example into a dotted
 line by turning off every other dot
 along its length.  Erase will turn
 off any dot, but you won't see it
 working unless the dot was already
 on.

- - - - - - - - - - - - - - - - - - -

HRIZLINE (49176) and VERTLINE (49173)

are SYSes that must be followed by

three numeric expressions separated

by commas.

  In HRIZLINE, the first and second

expressions are the left and right

points of the line.  The lesser will

always be used as the leftmost point.

If the first two expressions are

equal, HRIZLINE will plot a single

point.  The last expression is the

vertical position of the line.

  In VERTLINE, the first and second

expressions are the top and bottom

points of the line.  The lesser will

always be used as the top point.  If

the first two expressions are equal,

VERTLINE will plot a single point.

The last expression is the horizontal

position of the line.

======================================

  The machine-language SYSPLOTTERB

routines are on Side 2 of this issue

of LOADSTAR. They were written by

Ailing Gardner with the MERLIN

assembler.  James Gelatin Weiler has

written a BASIC program to

demonstrate the SYSPLOTTERB routines.

The demo program includes a

subroutine to print numbers and

letters on the high-resolution screen

to aid in graph making.

  If you wish to view the SYSPLOTTERB
\oad"plottext b demo",8
demo, press the '\' key now.

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