Jump Sprite - Move a sprite along a parabolic arc so it

 

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Have a sprite appear to "jump" along a parabolic arc. The arc direction can be concave or convex, and the beginning and end points of the arc can be adjusted. Useful for various game applications.

-- Make a sprite "jump" by moving it along a parabolic arc. -- Behavior by Ken Loge - kenl@ori.org -- 06-01-02 -- Based on an algorithm by Dan Livingston - dan@wire-man.com -- A variation of the standard parabola formula of y = x^2 -- Reworked to be more versatile, the formula is: -- y = h - (2 * sqrt(h) x/d - sqrt(h))^2 -- h = the height of the jump -- d = distance of the jump property pJumpLeft -- if true the sprite jumps to the left property pJumpRight -- if true the sprite jumps to the right property pJumpDirection -- stores the direction of each jump property pConvexArc -- sets the parabola type to convex property pConcaveArc -- sets the parabola type to concave property pArcDirection -- if 1, the arc is upward, if -1, the arc is downward property pSqrootHeight -- stores the square root of the height of the parabola property pWidthFactor property pXCounter -- keeps track of jump iteration values property pXHop property pXIncrement -- the "speed" of horizontal movement during a jump. Too big a number will "overshoot" the span. property pYInitial -- the original Y position of the sprite property pYFactor1 -- used to determine the sprite Y position during a jump property pYFactor2 property pYFactorFinal property pHeight -- the height of the curve property pDistance -- the horizontal span of the curve. The smaller this number, the faster the sprite will move. property pJump -- used to trigger jump movement on getBehaviorDescription me   return "Moves a sprite on a parabolic curve so it appears to jump in an arc." end on beginSprite me   pSqrootHeight = sqrt(pHeight)   pWidthFactor = (2.0 * pSqrootHeight) / pDistance   pYInitial = sprite(me.spriteNum).locV   pXCounter = 0   -- jumps will move to the right   if pJumpLeft = TRUE then pJumpDirection = -1   -- jumps will move to the left   if pJumpRight = TRUE then pJumpDirection =  1   -- set jumps to to the right if user checks both directions   if pJumpLeft AND pJumpRight = TRUE then pJumpDirection = 1   -- parabolic arc will be convex   if pConvexArc = TRUE then pArcDirection = 1   -- parabolic arc will be concave   if pConcaveArc = TRUE then pArcDirection =  -1   -- set to convex arc if user checks both   if pConvexArc AND pConcaveArc = TRUE then pArcDirection = 1 end on getPropertyDescriptionList me   list = [:]   addProp list, #pHeight, [#comment: "Height of jump:", #format: #integer, #default: 100, #range: [#min: 0, #max: 500]]   addProp list, #pDistance, [#comment: "Span of jump:", #format: #integer, #default: 150, #range: [#min: 0, #max: 600]]   addProp list, #pXIncrement, [#comment: "X offset per iteration:", #format: #integer, #default: 5, #range: [#min: 0, #max: 50]]   addProp list, #pJumpRight, [#comment: "Jump to the right:", #format: #boolean, #default: TRUE]   addProp list, #pJumpLeft, [#comment: "Jump to the left:", #format: #boolean, #default: FALSE]   addProp list, #pConvexArc, [#comment: "Convex arc:", #format: #boolean, #default: TRUE]   addProp list, #pConcaveArc, [#comment: "Concave arc:", #format: #boolean, #default: FALSE]   return list end on exitFrame me   if (pXCounter <= pDistance) AND pJump = TRUE then     -- set jumping height     pYFactor1 = (pWidthFactor * pXCounter) - pSqrootHeight     pYFactor2 = power(pYFactor1, 2)     pYFactorFinal = (pHeight - pYFactor2) * pArcDirection     -- pJumpDirection determines the direction of the jump     pXHop = pJumpDirection * pXIncrement     -- move the sprite     sprite(me.spriteNum).locH = sprite(me.spriteNum).locH + pXHop     sprite(me.spriteNum).locV = pYInitial - pYFactorFinal     -- prepare for next iteration     pXCounter = pXCounter + 5   else     -- move sprite back to original Y position to correct for iteration offset     --sprite(me.spriteNum).locV = pYInitial     -- reset so user can click the sprite again     pJump = FALSE     pXCounter = 0   end if end -- as written, each time the mouse is clicked the ball "jumps" on mouseUp me   -- toggle jump state   if pJump = FALSE then     pJump = TRUE   else     pJump = FALSE   end if end