'===========================================================================
' Subject: CONTAINED BOUNCING BALLS          Date: 10-26-97 (20:22)       
' Author:  William Deer                      Code: QB, QBasic, PDS        
' Origin:  ag312350@student.uq.edu.au      Packet: EGAVGA.ABC
'===========================================================================
' BALLS.BAS     by William DEER c/o. ag312350@student.uq.oz.au
'
' This program is really simple. It draws round blips on the screen and then
' moves them around, bouncing off the walls. You can change the size of the
' box and the pressure inside changes. Hit Escape to exit the program.

SCREEN 12
DIM X, Y, Box1, Box2, Boy1, Boy2, Dx, Dy, BlipNo, rad AS INTEGER
DIM A, C, D AS INTEGER
DIM Xpos, Ypos, Xvel, Yvel, FutX, FutY AS SINGLE
DIM STP, Pressure AS SINGLE
        RANDOMIZE (TIMER / 16)
X = 639: Y = 300                ' Screen Size
Box1 = 0: Box2 = X              ' Starting Coords for Box
Boy1 = 0: Boy2 = Y
Dx = 50: Dy = 50                ' Minimum Size of Box
BlipNo = 20                     ' Number of Blips
rad = 5                         ' Radius of Blips
STP = X * Y
Pressure = 1
DIM Blip(BlipNo, 6)             ' Array for Blip Information
DIM Ball(484) AS INTEGER:       ' Graphics Array for a square of side 10 pixels

CLS : CIRCLE (rad, rad), rad, 15: PAINT (rad, rad), 15, 15: GET (0, 0)-(10, 10), Ball: CLS

FOR A = 1 TO BlipNo             ' Initialise Blip Information
 Blip(A, 1) = ((RND * 50) + (X / 2))
 Blip(A, 2) = ((RND * 50) + (Y / 2))
 Blip(A, 5) = (RND * 5) + 1
 Blip(A, 6) = (RND * 5) + 1
 Blip(A, 3) = Blip(A, 5) * Pressure
 Blip(A, 4) = Blip(A, 6) * Pressure
 PUT (Blip(A, 1) - rad, Blip(A, 2) - rad), Ball, XOR    ' Draw Blips
NEXT A
A$ = " "
'               ----------------------
'               Start of the main loop
'               ----------------------
WHILE A$ <> CHR$(27) ' Hit <Esc> to end program
 IF A$ <> "" THEN
   LINE (Box1, Boy1)-(Box2, Boy2), 0, B    ' Erase Old Border Box
   ' Key has been pressed.
   SELECT CASE A$
    CASE "1": IF Boy2 - Boy1 > Dy THEN Boy1 = Boy1 + 1
    CASE "2": IF Boy1 > 0 THEN Boy1 = Boy1 - 1
    CASE "3": IF Boy2 - Boy1 > Dy THEN Boy2 = Boy2 - 1
    CASE "4": IF Boy2 < Y THEN Boy2 = Boy2 + 1
    CASE "5": IF Box2 - Box1 > Dx THEN Box1 = Box1 + 1
    CASE "6": IF Box1 > 0 THEN Box1 = Box1 - 1
    CASE "7": IF Box2 - Box1 > Dx THEN Box2 = Box2 - 1
    CASE "8": IF Box2 < X THEN Box2 = Box2 + 1
   END SELECT
  
 '  Calculate Pressure .: Relative Speed of Blips.
   Pressure = STP / ((ABS(Box2 - Box1) * ABS(Boy2 - Boy1)))
   FOR C = 1 TO BlipNo
    Blip(C, 3) = SGN(Blip(C, 3)) * Blip(C, 5) * Pressure
    Blip(C, 4) = SGN(Blip(C, 3)) * Blip(C, 6) * Pressure
   NEXT C
 ' Redraw Box and values in corners
   LINE (Box1, Boy1)-(Box2, Boy2), 14, B, X
   LOCATE 20, 1: PRINT "BALLS.BAS", , ;
   PRINT "Box Size =("; Box1; ","; Boy1; ")-("; Box2; ","; Boy2; ")";
   LOCATE 21, 1: PRINT "Keys are as follows;"
   LOCATE 22, 1: PRINT "<1> Lower Roof", "<2> Raise Roof"
   LOCATE 23, 1: PRINT "<3> Raise Floor", "<4> lower Floor"
   LOCATE 24, 1: PRINT "<5> Left wall in", "<6> Left wall out"
   LOCATE 25, 1: PRINT "<7> Right wall in", "<8> Right wall in"
   LOCATE 27, 30: PRINT "Pressure over STP = "; : PRINT USING "###.#"; Pressure;
   PRINT "    Ball No. = "; BlipNo;
   LOCATE 29, 1: PRINT "Press <Esc> to exit program ";
 END IF

 FOR C = 1 TO BlipNo
  Xpos = Blip(C, 1):            Ypos = Blip(C, 2)
  Xvel = Blip(C, 3):            Yvel = Blip(C, 4)
  FutX = Xpos + Xvel:           FutY = Ypos + Yvel
  IF FutX < Box1 + rad + 2 THEN Xvel = -1! * Xvel    ' Gone past the left wall
  IF FutX > Box2 - rad - 2 THEN Xvel = -1! * Xvel    ' Gone past the right wall
  IF FutY < Boy1 + rad + 2 THEN Yvel = -1! * Yvel    ' Gone past the top wall
  IF FutY > Boy2 - rad - 2 THEN Yvel = -1! * Yvel    ' Gone past the right wall
  Blip(C, 1) = Xpos + Xvel:     Blip(C, 2) = Ypos + Yvel
  Blip(C, 3) = Xvel:            Blip(C, 4) = Yvel
  PUT (Xpos - rad, Ypos - rad), Ball, XOR       ' Remove old ball image
  PUT (Blip(C, 1) - rad, Blip(C, 2) - rad), Ball, XOR   ' Put new image
 NEXT C
 A$ = INKEY$
WEND