Contents

Bouncing Ball

Added on 6/7/1999

Compatibilities:
behavior D6_5 Mac

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A behaviour to animate a bouncing ball using x:y co-ordinates rather than trigonometry Some of the code courtesy Direct-L. last Modification = 8:10 PM 17/10/97 MAF

property mySprite     -- the sprite Number of current sprite
property mySelf       -- the sprite me
property myWidth      -- the width of the animated sprite
property myHeight     -- the height of the animated sprite
property velocityV    -- the vertical velocity of the sprite
property velocityH    -- the horizontal velocity of the sprite
property speed        -- to set variations of speed of the sprite
property LastTicks    -- the tick count last time on enterframe
property randomSprite -- set sprite to random point at start if set
property collisionOn  -- set collision detection
property direction    -- direction sprite travelling in when hit
property hitMe        -- which side did I get hit from
property stOffset     -- offset for edge of stage

-- initialise Properties

on beginSprite me

  -- get the number, the width and the height of my sprite
  set mySprite = the SpriteNum of me
  set mySelf = sprite (the spriteNum of me)
  set myWidth  = the width of sprite mySprite
  set myHeight = the height of sprite mySprite

  -- set the speed of the objects
  set velocityV = random(speed)
  set velocityH = random(speed)
  set LastTicks = 0

  -- assign a random starting location for the object
  if randomSprite = true then
    set stageHeight = the stageBottom - the stageTop
    set stageWidth = the stageRight - the stageLeft
    set the locV of sprite mySprite to random((stageHeight) - 100) + 50
    set the locH of sprite mySprite to random((stageWidth) - 100) + 50
  end if

  -- add the sprite number to global list
  addAt the actorList mySprite, mySprite

end beginSprite

-- End processes

on endSprite me

  -- clean up the spritelist
  deleteOne the actorList mySprite

end endSprite

-- Animate the Sprite

on enterFrame me

  --save the ticks
  set LastTicks = (the ticks)

  -- increment position of sprite based on its velocity
  set currentV = the locV of sprite mySprite + velocityV
  set currentH = the locH of sprite mySprite + velocityH

  -- check to see if it is off the top or bottom of the stage
  -- turn it around if it is

  if currentV < (integer(myHeight/2) + stOffset) then
    set velocityV = -1 * velocityV
    set currentV = (integer(myHeight/2) + stOffset)
  end if

  if currentV > (the stageBottom - the stageTop) - (integer(myHeight/2) + stOffset) then
    set velocityV = -1 * velocityV
    set currentV = (the stageBottom - the stageTop) - (integer(myHeight/2) + stOffset)
  end if

  -- check to see if it is off the left or right of the stage
  -- turn it around if it is
  if currentH < (integer(myWidth/2) + stOffset) then
    set velocityH = -(1 * velocityH)
    set currentH = (integer(myWidth/2) + stOffset)
  end if
  if currentH > (the stageRight - the stageLeft) - (integer(myWidth/2) + stOffset) then
    set velocityH = -(1 * velocityH)
    set currentH = (the stageRight - the stageLeft) - (integer(myWidth/2) + stOffset)
  end if

  -- update its location on the stage
  set the loc of sprite mySprite = point(currentH,currentV)

  -- if collision detection on
  if collisionOn = true then

    -- collision detection procedure between sprites
    collisionDetect
  end if

end enterFrame

-- detect collision of two sprites

on collisionDetect

  -- check all sprites with this behaviour
  repeat with listPos = 1 to count(the actorList)
    set otherSprite = getOne(the actorList, listPos)

    -- if the other sprite isn't referring to me
    if otherSprite <> mySprite then

      -- check to see it is within my circle
      -- uses a circle with radius of half sprite width
      circleIntersect mySprite otherSprite
      if the result = TRUE then
        -- check for how collision occurred
        checkCollision otherSprite
      end if
    end if
  end repeat

end collisionDetect

-- check whether sprite is within a specified circle of another sprite

on circleIntersect sprite1, sprite2

  -- sprite1 and sprite2 are channel numbers containing circle sprites
  -- first get the radii of the circles
  set circle1Radius = the width of sprite sprite1 / 2
  set circle2Radius = the width of sprite sprite2 / 2

  -- next determine the required distance between the two centerpoints for non-intersection
  set minDistanceForNonIntersect = circle1Radius + circle2Radius

  -- now determine the actual distance between the centerpoints of the two sprites
  set actualDistance = distance (the loc of sprite sprite1 + point(circle1Radius, circle1Radius), the loc of sprite sprite2 + point(circle2Radius, circle2Radius))

  -- now compare the two and return if within circle
  if actualDistance > minDistanceForNonIntersect then
    return FALSE
  else
    return TRUE
  end if

end circleIntersect

-- compute distance between two points

on distance point1, point2
  set deltaH = the locH of point1 - the locH of point2
  set deltaV = the locV of point1 - the locV of point2
  --return actual distance between the two points
  return sqrt(deltaH * deltaH + deltaV * deltaV)
end distance

-- check rects of sprites and overlap for collision direction

on checkCollision otherSprite

  -- the sprite can be travelling in 1 of 8 directions & can be hit from 1 of 8 directions.
  -- calculate 8 segments of circle as 1 through 8 from velocityH & velocityV
  -- calculate the 8 directions sprite can be hit from by subtracting Loc of other sprite
  -- from my sprite and using locH and locV values of the result.

  -- calculate the direction in which the sprite is hit from by another sprite
  set delta = the loc of sprite mySprite - the loc of sprite otherSprite
  set deltaX = the locH of delta        -- horizontal difference between sprites
  set deltaY = the locV of delta        -- vertical difference between sprites

  if deltaX >= 0 then
    if deltaY >= 0 then
      if abs(deltaX) >= abs(DeltaY) then set hitMe = 1
      else set hitMe = 2
    else
      if abs(deltaX) >= abs(DeltaY) then set hitMe = 8
      else set hitMe = 7
    end if
  else
    if deltaY >= 0 then
      if abs(deltaX) >= abs(DeltaY) then set hitMe = 4
      else set hitMe = 3
    else
      if abs(deltaX) >= abs(DeltaY) then set hitMe = 5
      else set hitMe = 6
    end if
  end if

  -- calculate the direction in which the sprite is travelling
  if velocityH <= 0 then
    if velocityV <= 0 then
      if abs(velocityH) >= abs(velocityV) then set direction = 1
      else set direction = 2
    else
      if abs(velocityH) >= abs(velocityV) then set direction = 8
      else set direction = 7
    end if
  else
    if VelocityV <= 0 then
      if abs(velocityH) >= abs(velocityV) then set direction = 4
      else set direction = 3
    else
      if abs(velocityH) >= abs(velocityV) then set direction = 5
      else set direction = 6
    end if
  end if

  -- set x and y to absolute values of velocityH and velocityV for ease of calculation
  set x = abs(velocityH)
  if x = 0 then set x = 1   -- set to 1 to avoid divide by 0 errors
  set y = abs(velocityV)
  if y = 0 then set y = 1   -- set to 1 to avoid divide by 0 errors

  case direction of
    1:
      case hitMe of
        1:
          set velocityH = x
          set velocityV = x - y
        2:
          set velocityH = -1 * (x * y/x)
          set velocityV = y * x/y
        4,3:
          set velocityV = y
        5:
          set velocityV = -1 * (x - y)
        6,7:
          set velocityH = -1 * (x * y/x)
          set velocityV = -1 * (y * x/y)
        8:
          set velocityH = x * y/x
          set velocityV = -1 * (y * x/y)
      end case
    2:
      case hitMe of
        2:
          set velocityH = y - x
          set velocityV = y
        3:
          set velocityH = -1 * (x * y/x)
          set velocityV = y * x/y
        5,4:
          set velocityH = -1 * (x * y/x)
          set velocityV = -1 * (y * x/y)
        6:
          set velocityH = -1 * (y - x)
        7,8:
          set velocityH = x
        1:
          set velocityH = x * y/x
          set velocityV = -1 * (y * x/y)
      end case
    3:
      case hitMe of
        2:
          set velocityH = x * y/x
          set velocityV = y * x/y
        3:
          set velocityH = -1 * (y - x)
          set velocityV = y
        4:
          set velocityH = -1 * (x * y/x)
          set velocityV = -1 * (y * x/y)
        6,5:
          set velocityH = -1 * x
        7:
          set velocityH = y - x
        8,1:
          set velocityH = x * y/x
          set velocityV = -1 * (y * x/y )
      end case
    4:
      case hitMe of
        1,2:
          set velocityV = y
        3:
          set velocityH = x * y/x
          set velocityV = y * x/y
        4:
          set velocityH = -1 * x
          set velocityV = x - y
        5:
          set velocityH = -1 * (x * y/x)
          set velocityV = -1 * (y * x/y)
        7,6:
          set velocityH = x * y/x
          set velocityV = -1 * (y * x/y)
        8:
          set velocityV = -1 * (x - y)
      end case
    5:
      case hitMe of
        1:
          set velocityV = x - y
        2,3:
          set velocityH = x * y/x
          set velocityV = y * x/y
        4:
          set velocityH = -1 * (x * y/x)
          set velocityV = y * x/y
        5:
          set velocityH = -1 * x
          set velocityV = -1 * (x - y)
        6:
          set velocityH = x * y/x
          set velocityV = -1 * (y * x/y)
        8,7:
          set velocityV = -1 * y
      end case
    6:
      case hitMe of
        1,8:
          set velocityH = x * y/x
          set velocityV = y * x/y
        2:
          set velocityH = y - x
        3,4:
          set velocityH = -1 * x
        5:
          set velocityH = -1 * (x * y/x)
          set velocityV = y * x/y
        6:
          set velocityH = -1 * (y - x)
          set velocityV = -1 * y
        7:
          set velocityH = x * y/x
          set velocityV = -1 * (y * x/y)
      end case
    7:
      case hitMe of
        8:
          set velocityH = x * y/x
          set velocityV = y * x/y
        2,1:
          set velocityH = x
        3:
          set velocityH = -1 * (y - x)
        4,5:
          set velocityH = -1 * (x * y/x)
          set velocityV = y * x/y
        6:
          set velocityH = -1 * (x * y/x)
          set velocityV = -1 * (y * x/y)
        7:
          set velocityH = y - x
          set velocityV = -1 * y
      end case
    8:
      case hitMe of
        1:
          set velocityH = x * y/x
          set velocityV = y * x/y
        3,2:
          set velocityH =  -1 * (x * y/x)
          set velocityV =  y * x/y
        4:
          set velocityV = x - y
        5,6:
          set velocityV = -1 * y
        7:
          set velocityH = -1 * (x * y/x)
          set velocityV = -1 * (y * x/y)
        8:
          set velocityH = x
          set velocityV = -1 * (x - y)
      end case
  end case
end checkCollision

-- create a Property List
on getPropertyDescriptionList
  set p_list = [#speed: [ #default:10, #format:#integer, #comment:"Set the sprite speed",#range: [#min:0,#Max:30]],¬
#stOffset: [ #default:0, #format:#integer, #comment:"Offset for the edge of stage",#range: [#min:0,#Max:50]],¬
#randomSprite:[#default:1,#format:#boolean,#comment:"Start from random point?"],¬
#collisionOn:[#default:1,#format:#boolean,#comment:"Collision detection on?"]]
  return p_list
end getPropertyDescriptionList

-- create a Behaviour Description
on getBehaviorDescription
  put "A sprite behaviour that bounces the sprite around the screen like a frictionless " into line1
  put "ball. Collision detection can be switched on that allows sprites to bounce of " into line2
  put "one another. Animation speed is set by the number of pixels. " &RETURN & RETURN  into line3
  put "There are also other functions to modify this behaviour: " & RETURN into line4
  put "1. Stage Offset - to inset the edge of the screen used. " & RETURN into line5
  put "2. Random start - sprite starts from random point. " into line6
  return line1 & line2 & line3 & line4 & line5 & line6
end getBehaviorDescription

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