PSET

The PSET grahics SCREEN statement sets a pixel to a coordinate with a default or designated color attribute.

Syntax

PSET [STEP](column%, row%)[, colorAttribute]

Can use STEP relative graphics coordinates from a previous graphic object.
Column and row can be literal or variable INTEGER coordinates values which can be offscreen.
If the colorAttribute is omitted, PSET will use the current destination page's _DEFAULTCOLOR.

Usage:

Color attributes are limited to the SCREEN mode used. Any color value other than 0 will be white in SCREENs 2 or 11.
PSET can locate other graphics objects and color DRAW statements.
The PSET action can be used in a graphics PUT to produce an identical image on any background.
The graphic cursor is set to the center of the program window on program start for STEP relative coordinates.
PSET can be used in any graphic screen mode, but cannot be used in the default screen mode 0 as it is text only! (Or in any _NEWIMAGE(x, y, 0) screens which are text only as well.)

Example: Using PSET to locate and color a DRAW statement.

SCREEN 12
PSET(100, 100), 12
DRAW "U20 R20 D20 L20"

Screen results: A drawn box that is bright red.

Example 2: Magnifying a box portion of a Mandelbrot image with PSET

DEFSTR A-Z
DIM red(15) AS INTEGER, green(15) AS INTEGER, blue(15) AS INTEGER
DIM i AS INTEGER
SCREEN 12
FOR i = 0 TO 15: READ red(i): NEXT
FOR i = 0 TO 15: READ green(i): NEXT
FOR i = 0 TO 15: READ blue(i): NEXT
FOR i = 0 TO 15: PALETTE i, 65536 * blue(i) + 256& * green(i) + red(i): NEXT
DATA 0,63,63,63,63,63,31, 0, 0,31,31,31,47,63,63,63
DATA 0, 0,15,31,47,63,63,63,63,31,15, 0, 0, 0, 0, 0
DATA 0, 0, 0, 0, 0, 0, 0, 0,31,63,63,63,63,63,42,21

DIM dmag AS INTEGER, dlogmag AS INTEGER
DIM a AS DOUBLE, b AS DOUBLE, mag AS DOUBLE
DIM dx AS INTEGER, dy AS INTEGER
DIM mx AS INTEGER, my AS INTEGER, mz AS INTEGER

dmag = 16
mag = 1

a = -.75
b = 0
DO
  DIM limitx AS DOUBLE, limit AS INTEGER
  DIM inc AS DOUBLE, left AS DOUBLE, top AS DOUBLE

  limitx = 150 * (LOG(mag) + 1)
  IF limitx > 32767 THEN limitx = 32767
  limit = INT(limitx)
  inc = .004 / mag
  left = a - inc * 319
  top = b + inc * 239
  CLS

  DIM yy AS INTEGER, xx AS INTEGER
  DIM x AS DOUBLE, y AS DOUBLE, z AS INTEGER

  FOR yy = 0 TO 479
    y = top - inc * yy
    FOR xx = 0 TO 639
        x = left + inc * xx
        z = mandel(x, y, limit)
        IF z < limit THEN PSET (xx, yy), 1 + z MOD 15
        IF INKEY$ = CHR$(27) THEN SYSTEM
    NEXT
  NEXT
  mz = 0
  CALL readmouse(mx, my, mz)
  DO
    dx = 319 \ dmag
    dy = 239 \ dmag
    CALL readmouse(mx, my, mz)
    IF mz THEN EXIT DO
    CALL rectangle(mx - dx, my - dy, mx + dx, my + dy)
    DIM t AS DOUBLE
    t = TIMER
    WHILE t = TIMER
      key$ = INKEY$
      SELECT CASE key$
        CASE CHR$(27)
          SYSTEM
        CASE CHR$(0) + CHR$(72)
          dmag = dmag \ 2
          IF dmag < 2 THEN dmag = 2
        CASE CHR$(0) + CHR$(80)
          dmag = dmag * 2
          IF dmag > 128 THEN dmag = 128
      END SELECT
    WEND
    CALL rectangle(mx - dx, my - dy, mx + dx, my + dy)
  LOOP
  a = a + inc * (mx - 319): b = b - inc * (my - 239)
  IF (mz = 1) THEN mag = dmag * mag ELSE mag = mag / dmag
  IF (mag < 1) THEN mag = 1
LOOP

FUNCTION mandel% (x AS DOUBLE, y AS DOUBLE, limit AS INTEGER)
  DIM a AS DOUBLE, b AS DOUBLE, t AS DOUBLE
  DIM n AS INTEGER
  n = 0: a = 0: b = 0
  DO
    t = a * a - b * b + x
    b = 2 * a * b + y: a = t
    n = n + 1
  LOOP UNTIL a * a + b * b > 4 OR n > limit
  mandel = n
END FUNCTION

SUB readmouse (x AS INTEGER, y AS INTEGER, z AS INTEGER)
z=0
DO
if _MOUSEBUTTON(1) THEN z = z OR 1
if _MOUSEBUTTON(2) THEN z = z OR 2
if _MOUSEBUTTON(3) THEN z = z OR 4
LOOP UNTIL _MOUSEINPUT=0
x=_MOUSEX
y=_MOUSEY
END SUB

SUB rectangle (x1 AS INTEGER, y1 AS INTEGER, x2 AS INTEGER, y2 AS INTEGER)
  DIM i AS INTEGER, j AS INTEGER
  FOR i = x1 TO x2
    j = POINT(i, y1)
    PSET (i, y1), j XOR 15
    j = POINT(i, y2)
    PSET (i, y2), j XOR 15
  NEXT
  FOR i = y1 TO y2
    j = POINT(x1, i)
    PSET (x1, i), j XOR 15
    j = POINT(x2, i)
    PSET (x2, i), j XOR 15
  NEXT
END SUB

Code by Codeguy

Notes: Left click, to zoom in on the rectangle. Right click, to zoom out. Up arrow makes the rectangle bigger and down arrow makes the rectangle smaller.

PSET

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PSET

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