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PSET

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Samuel Gomes edited this page Nov 8, 2022 · 1 revision

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

Syntax

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

Parameter(s)

  • 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 _DEST page's _DEFAULTCOLOR.

Usage

  • Color attributes are limited to the SCREEN mode used. Any color value other than 0 will be white in SCREEN (statement)s 2 or 11.
  • PSET can locate other graphics objects and color DRAW statements.
  • The PSET action can be used in a graphics PUT (graphics statement) 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(s)

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.

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

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.

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