WINDOW Statement

 Action

 Defines the dimensions of the current graphics viewport window.

 Syntax


  WINDOW  SCREEN ( x1!,  y1!)  - ( x2!,  y2!)


 Remarks

 The  WINDOW statement allows the user to create a customized coordinate
 system to draw lines, graphs, or objects without being constrained by the
 physical coordinate values and orientation of the graphics viewport. This is
 done by redefining the graphics viewport coordinates with the "view
 coordinates" ( x1!,  y1!) and ( x2!,  y2!). These view coordinates are
 single-precision numbers.

  WINDOW defines a coordinate system that is mapped to the physical
 coordinates of the viewport. All subsequent graphics statements use the
 window coordinates and are displayed within the current viewport. (The size
 of the viewport can be changed with the  VIEW statement.)

 The  RUN statement, or  WINDOW with no arguments, disables the window
 transformation. (The window coordinates are the same as the viewport
 coordinates.) The  WINDOW SCREEN variant inverts the normal Cartesian
 direction of the y coordinate, so y values go from negative to positive from
 top to bottom.

 Figure 1.1 shows the effects of  WINDOW and  WINDOW SCREEN on a line drawn
 in screen mode 2. Notice the change in the coordinates of the screen
 corners.

 See Also


  SCREEN Statement,  VIEW,  WIDTH

 Example


 The following example uses BASIC graphics statements to generate a fractal.
 This fractal shows a subset of a class of numbers known as complex numbers;
 this subset is called the "Mandelbrot Set," named after an IBM researcher.
 The program uses the  VIEW,  WINDOW,  PMAP, and  PSET statements.

 DEFINT A-Z         ' Default variable type is integer.

 DECLARE SUB ScreenTest (EM%, CR%, VL%, VR%, VT%, VB%)



 ' Set maximum number of iterations per point.

 CONST MAXLOOP = 30, MAXSIZE = 1000000

 CONST FALSE = 0, TRUE = NOT FALSE       ' Boolean constants.

 ' Set window parameters.

 CONST WLeft = -1000, WRight = 250, WTop = 625, WBottom = -625



 ' Call ScreenTest to find out if this is an EGA machine,

 ' and get coordinates of viewport corners.

 ScreenTest EgaMode, ColorRange, VLeft, VRight, VTop, VBottom



 ' Define viewport and corresponding window.

 VIEW (VLeft, VTop)-(VRight, VBottom), 0, ColorRange

 WINDOW (WLeft, WTop)-(WRight, WBottom)



 LOCATE 24, 10. PRINT "Press any key to quit.";

 XLength = VRight - VLeft

 YLength = VBottom - VTop

 ColorWidth = MAXLOOP \ ColorRange



 ' Loop through each pixel in viewport and calculate

 '  whether or not it is in the Mandelbrot Set.

 FOR Y = 0 TO YLength       ' Loop through every line in the viewport.

    LogicY = PMAP(Y, 3)     ' Get the pixel's logical y coordinate.

    PSET (WLeft, LogicY)    ' Plot leftmost pixel in the line.

    OldColor = 0            ' Start with background color.

    FOR X = 0 TO XLength    ' Loop through every pixel in the line.

       LogicX = PMAP(X, 2)  ' Get the pixel's logical x coordinate.

       MandelX& = LogicX

       MandelY& = LogicY

       ' Do the calculations to see if this point is in

       '  the Mandelbrot Set.

       FOR I = 1 TO MAXLOOP

          RealNum& = MandelX& * MandelX&

          ImagNum& = MandelY& * MandelY&

          IF (RealNum& + ImagNum&) >= MAXSIZE THEN EXIT FOR

          MandelY& = (MandelX& * MandelY&) \ 250 + LogicY

          MandelX& = (RealNum& - ImagNum&) \ 500 + LogicX

       NEXT I

 ' Assign a color to the point.

       PColor = I \ ColorWidth

       ' If color has changed, draw a line from the

       ' last point referenced to the new point,

       '  using the old color.

       IF PColor <> OldColor THEN

          LINE -(LogicX, LogicY), (ColorRange - OldColor)

          OldColor = PColor

       END IF

       IF INKEY$ <> "" THEN END

    NEXT X

    ' Draw the last line segment to the right edge of

    '  the viewport.

    LINE -(LogicX, LogicY), (ColorRange - OldColor)

 NEXT Y

 DO . LOOP WHILE INKEY$ = ""

 SCREEN 0, 0             ' Restore the screen to text mode,

 WIDTH 80                ' 80 columns.

 END



 BadScreen.              ' Error handler that is invoked if

    EgaMode = FALSE      '  there is no EGA graphics card.

    RESUME NEXT



 ' The ScreenTest SUB procedure tests to see if user has EGA hardware

 ' EGA hardware with SCREEN 8. If this causes an error, the EM flag

 ' is set to FALSE, and the screen is set with SCREEN 1. ScreenTest

 ' also sets values for corners of viewport (VL = left, VR = right,

 ' VT = top, VB = bottom), scaled with the correct aspect ratio so

 ' that the viewport is a perfect square.

 SUB ScreenTest (EM, CR, VL, VR, VT, VB) STATIC

    EM = TRUE

    ON ERROR GOTO BadScreen

    SCREEN 8, 1

    ON ERROR GOTO 0

    IF EM THEN           ' No error, so SCREEN 8 is OK.

       VL = 110. VR = 529

       VT = 5. VB = 179

       CR = 15           ' 16 colors (0 - 15).

    ELSE                 ' Error, so use SCREEN 1.

       SCREEN 1, 1

       VL = 55. VR = 264

       VT = 5. VB = 179

       CR = 3            ' 4 colors (0 - 3).

    END IF

 END SUB